Urine pH and Citrate as Predictors of Calcium Phosphate Stone Formation

Key Points

The occurrence of calcium phosphate stones has increased over the past five decades, and this is most notable in female stone formers. High urine pH and hypocitraturia are the most discriminatory urine parameters between calcium phosphate and calcium oxalate stone formers. High urine pH in calcium phosphate stone formers is independent of the effect of dietary alkali and acid.

Background

Urinary parameters, including urine pH and citrate, are recognized as critical in the pathophysiology of calcium-based stones. The factors contributing to variation in these parameters between calcium oxalate (CaOx) and calcium phosphate (CaP) stone formers (SFs) are, however, not well-understood. In this study, using readily available laboratory data, we explore these differences to delineate the odds of forming CaP versus CaOx stones.

Methods

In this single-center retrospective study, we compared serum and urinary parameters between adult CaP SFs, CaOx SFs, and non–stone formers.

Results

Urine pH was higher and urine citrate lower in CaP SFs compared with same-sex CaOx SFs and non–stone formers. In CaP SFs, higher urine pH and lower citrate were independent of markers of dietary acid intake and gastrointestinal alkali absorption, suggesting abnormal renal citrate handling and urinary alkali excretion. In a multivariable model, urine pH and urine citrate were most discriminatory between CaP SFs and CaOx SFs (receiver-operating characteristic area under the curve of 0.73 and 0.65, respectively). An increase in urine pH by 0.35, a decrease in urine citrate by 220 mg/d, a doubling of urine calcium, and female sex all independently doubled the risk of CaP stone formation compared with CaOx stones.

Conclusions

High urine pH and hypocitraturia are two clinical parameters that distinguish the urine phenotype of CaP SFs from CaOx SFs. Alkalinuria is due to intrinsic differences in the kidney independent of intestinal alkali absorption and is accentuated in the female sex.

Patients' Experiences With the Removal of a Ureteral Stent: Insights From In-depth Interviews With Participants in the USDRN STENTS Qualitative Cohort Study

OBJECTIVE

To describe the experiences of patients undergoing stent removal in the USDRN Study to Enhance Understanding of Stent-Associated Symptoms (STENTS), a prospective, observational cohort study of patients with short-term ureteral stent placement post-ureteroscopy.

METHODS

We conducted a qualitative descriptive study using in-depth interviews. Participants reflected on (1) painful or bothersome aspects of stent removal, (2) symptoms immediately after removal, and (3) symptoms in the days following removal. Interviews were audio-recorded, transcribed, and analyzed using applied thematic analysis.

RESULTS

The 38 participants interviewed were aged 13-77 years, 55% female, and 95% White. Interviews were conducted 7-30 days after stent removal. Almost all participants (n = 31) described that they experienced either pain or discomfort during stent removal, but for most (n = 25) pain was of short duration. Many participants (n = 21) described anticipatory anxiety related to the procedure, and several (n = 11) discussed discomfort arising from lack of privacy or feeling exposed. Interactions with medical providers often helped put participants at ease, but also increased discomfort for some. Following stent removal, several participants described lingering pain and/or urinary symptoms, but these largely resolved within 24 hours. A few participants described symptoms persisting for more than a day post stent removal.

CONCLUSION

These findings on patients' experiences during and shortly after ureteral stent removal, particularly the psychological distress they experienced, identify opportunities for improvement in patient care. Clear communication from providers about what to expect with the removal procedure, and the possibility of delayed pain, may help patients adapt to discomfort.

The Patient Voice: Stent Experiences After Ureteroscopy-Insights from In-Depth Interviews with Participants in the USDRN STENTS Nested Qualitative Cohort Study

Purpose: Ureteral stents are commonly used after ureteroscopy and cause significant discomfort, yet qualitative perspectives on patients' stent experiences remain unknown. We describe psychological, functional, and interpersonal effects of post-ureteroscopy stents and whether additional patient-reported assessments may be needed. Materials and Methods: Using a qualitative descriptive study design, we conducted in-depth interviews with a nested cohort of participants in the STudy to Enhance uNderstanding of sTent-associated Symptoms (STENTS). Participants shared their symptoms with a post-ureteroscopy stent and described symptom bother and impact on daily activities. All interviews were audio-recorded, transcribed, and analyzed using applied thematic analysis. During analysis, participants' experiences with interference in daily activities were categorized into three groups based on their impact: minimal, moderate, and substantial. Results: All 39 participants experienced pain, although descriptions varied and differentiated between feelings of pain vs discomfort. Almost all experienced urinary symptoms. Only a few reported other physical symptoms, although several psychological aspects were identified. In the areas of sleep, mood, life enjoyment, work, exercise, activities of daily living, driving, childcare, and leisure/social activities, the stent had little impact on daily living among participants placed in the minimal group (n = 12) and far greater impact for participants in the substantial group (n = 8). For patients in the moderate group (n = 19), some daily activities were moderately or substantially affected, whereas other activities were minimally affected. Conclusions: Counseling to better prepare patients for the impact of stent-associated symptoms may help mitigate symptom burden. While existing instruments adequately cover most symptoms, additional assessments for other domains, particularly psychological factors, may be needed.

Risk Factors for Increased Stent-associated Symptoms Following Ureteroscopy for Urinary Stones: Results From STENTS

PURPOSE

The STudy to Enhance uNderstanding of sTent-associated Symptoms sought to identify risk factors for pain and urinary symptoms, as well as how these symptoms interfere with daily activities after ureteroscopy for stone treatment.

MATERIALS AND METHODS

This prospective observational cohort study enrolled patients aged ≥12 years undergoing ureteroscopy with ureteral stent for stone treatment at 4 clinical centers. Participants reported symptoms at baseline; on postoperative days 1, 3, 5; at stent removal; and day 30 post-stent removal. Outcomes of pain intensity, pain interference, urinary symptoms, and bother were captured with multiple instruments. Multivariable analyses using mixed-effects linear regression models were identified characteristics associated with increased stent-associated symptoms.

RESULTS

A total of 424 participants were enrolled. Mean age was 49 years (SD 17); 47% were female. Participants experienced a marked increase in stent-associated symptoms on postoperative day 1. While pain intensity decreased ∼50% from postoperative day 1 to postoperative day 5, interference due to pain remained persistently elevated. In multivariable analysis, older age was associated with lower pain intensity (P = .004). Having chronic pain conditions (P < .001), prior severe stent pain (P = .021), and depressive symptoms at baseline (P < .001) were each associated with higher pain intensity. Neither sex, stone location, ureteral access sheath use, nor stent characteristics were drivers of stent-associated symptoms.

CONCLUSIONS

In this multicenter cohort, interference persisted even as pain intensity decreased. Patient factors (eg, age, depression) rather than surgical factors were associated with symptom intensity. These findings provide a foundation for patient-centered care and highlight potential targets for efforts to mitigate the burden of stent-associated symptoms.

Bone health outcomes in post-lung transplant patients with cystic fibrosis

BACKGROUND

Osteoporosis is a common comorbidity in patients with cystic fibrosis (CF). Although lung transplantation (LTx) improves quality of life of CF patients, there is little research examining long-term bone health outcomes following LTx in these patients.

METHODS

Data were collected on 59 patients who underwent LTx between 2006 and 2019, including 30 with CF and 29 without CF. We compared baseline characteristics, long-term bone mineral density (BMD) trends, and fracture incidence between the two patient populations, and examined factors associated with post-LTx fractures in CF patients.

RESULTS

Compared with non-CF patients, patients with CF were younger, had lower body mass index, and lower baseline BMD Z-scores at the lumbar spine, femoral neck, and total hip (all p<0.001). BMD at all sites declined in both groups in the first year post-LTx. In subsequent years, CF patients exhibited better BMD recovery relative to pre-transplantation, but continued to have lower BMD post-LTx. Post-transplant fractures occurred in 30% and 34% of CF and non-CF patients, respectively. CF patients who developed fractures after LTx had significantly lower BMD and lower pre-transplantation percent predicted forced expiratory volume in one second (FEV1%).

CONCLUSIONS

Although CF patients exhibit better BMD recovery following LTx compared to their non-CF counterparts, CF patients start with significantly lower pre-LTx BMD and experience a similarly high rate of post-LTx fractures. These findings highlight the unique contribution of the CF disease process to bone health, as well as a clear need for better prevention and treatment of osteoporosis in CF patients before and after LTx.

Type 4 renal tubular acidosis and uric acid nephrolithiasis: two faces of the same coin?

PURPOSE OF REVIEW

The present review summarizes findings of recent studies examining the epidemiology, pathophysiology, and treatment of type 4 renal tubular acidosis (RTA) and uric acid nephrolithiasis, two conditions characterized by an abnormally acidic urine.

RECENT FINDINGS

Both type 4 RTA and uric acid nephrolithiasis disproportionately occur in patients with type 2 diabetes and/or chronic kidney disease. Biochemically, both conditions are associated with reduced renal ammonium excretion resulting in impaired urinary buffering and low urine pH. Reduced ammoniagenesis is postulated to result from hyperkalemia in type 4 RTA and from insulin resistance and fat accumulation in the renal proximal tubule in uric acid nephrolithiasis. The typical biochemical findings of hyperkalemia and systemic acidosis of type 4 RTA are rarely reported in uric acid stone formers. Additional clinical differences between the two conditions include findings of higher urinary uric acid excretion and consequent urinary uric acid supersaturation in uric acid stone formers but not in type 4 RTA.

SUMMARY

Type 4 RTA and uric acid nephrolithiasis share several epidemiological, clinical, and biochemical features. Although both conditions may be manifestations of diabetes mellitus and thus have a large at-risk population, the means to the shared biochemical finding of overly acidic urine are different. This difference in pathophysiology may explain the dissimilarity in the prevalence of kidney stone formation.

Evaluation of an association between RANKL and OPG with bone disease in people with cystic fibrosis

BACKGROUND

As people with Cystic Fibrosis (CF) live longer, extra-pulmonary complications such as CF-related bone disease (CFBD) are becoming increasingly important. The etiology of CFBD is poorly understood but is likely multifactorial. Bones undergo continuous remodeling via pathways including RANK (receptor activator of NF-κB)/sRANKL (soluble ligand)/OPG (osteoprotegerin). We sought to examine the association between sRANKL (stimulant of osteoclastogenesis) and OPG levels (inhibitor of osteoclast formation) and CFBD to investigate their potential utility as biomarkers of bone turnover in people with CF.

METHODS

We evaluated sRANKL and OPG in plasma from people with CF and healthy controls (HC) and compared levels in those with CF to bone mineral density results. We used univariable and multivariable analysis to account for factors that may impact sRANKL and OPG.

RESULTS

We found a higher median [IQR] sRANKL 10,896pg/mL [5,781-24,243] CF; 2,406pg.mL [659.50-5,042] HC; p= 0.0009), lower OPG 56.68pg/mL [36.28-124.70] CF; 583.20pg/mL [421.30-675.10] HC; p < 0.0001), and higher RANKL/OPG in people with CF no BD than in HC (p < 0.0001). Furthermore, we found a higher RANKL/OPG ratio 407.50pg/mL [214.40-602.60] CFBD; 177.70pg/mL [131.50-239.70] CF no BD; p = 0.007) in people with CFBD versus CF without bone disease. This difference persisted after adjusting for variables thought to impact bone health.

CONCLUSIONS

The current screening recommendations of imaging for CFBD may miss important markers of bone turnover such as the RANKL/OPG ratio. These findings support the investigation of therapies that modulate the RANK/RANKL/OPG pathway as potential therapeutic targets for bone disease in CF.

Alkali Citrate Content of Common Over-the-Counter and Medical Food Supplements

Objective: Potassium citrate effectively decreases kidney stone recurrence, but it is costly and associated with side effects. While several over-the-counter supplements and medical foods purport to provide sufficient citrate to prevent recurrent stones, corroborating data on their actual citrate content is limited. Materials and Methods: Nine common nonprescription products were purchased online. Reported citrate content was obtained from packaging, promotional materials, or ingredient labels. Using a single serving of each product, actual citrate, sodium, potassium, calcium, magnesium, and oxalate content was measured using spectrophotometry and chromatography. Total alkali citrate, cost, and amounts of each component per 10 mEq of alkali citrate were also calculated. Results: Nearly all products contained more citrate than advertised, except for Litholyte^® powder, Litholyte^® Coffee, and Horbäach^® potassium citrate. Per serving, Moonstone^® powder, LithoBalance™, and KSP tabs™ contained the most citrate (means of 63.9, 33.5, and 26.9 mEq, respectively). Moonstone and LithoBalance had the greatest discrepancy between total citrate and alkali citrate (15.7 and 11.8 mEq per serving, respectively). NOW^® potassium citrate was least expensive ($0.04/10 mEq alkali citrate). KSP tabs delivered the most daily sodium (mean 158 mg/10 mEq alkali citrate, Litholyte Coffee provided the most potassium (mean of 13 mEq/10 mEq alkali citrate), and Kidney COP^® provided the most calcium (mean 147 mg/10 mEq alkali citrate). Conclusion: Some common over-the-counter products contain sufficient alkali to potentially promote a citraturic response; Moonstone provides the most alkali citrate, but at a higher cost than other products. Sodium, potassium, and calcium from these products must also be considered in daily consumption.

Romosozumab-aqqg in the Treatment of Osteoporosis in a Patient With Hypophosphatasia

Hypophosphatasia is a rare, inherited condition that causes osteomalacia and recurrent fractures. Therapeutic options for osteoporosis in patients with hypophosphatasia are limited because of concerns for a greater likelihood of atypical femoral fractures with antiresorptive agents. We report here the case of a patient with hypophosphatasia and osteoporosis who was treated with romosozumab-aqqg (Romo). An 81-year-old woman presented for management of osteoporosis with multiple fractures. She experienced a decline in bone mineral density over 20 years despite sequential osteoporosis treatment with oral bisphosphonates, hormone replacement therapy, teriparatide, and denosumab. Hypophosphatasia was suspected because of low serum alkaline phosphatase levels and was confirmed by genetic testing. After diagnosing hypophosphatasia, bone mineral density continued to decline and a trial of Romo was begun. After 1 year of Romo therapy, bone mineral density improved by 21%, and 10% at the lumbar spine and total hip, respectively. These changes were substantially greater than what she had experienced with prior teriparatide therapy. Blood alkaline phosphatase remained low on Romo. To our knowledge, this is the first report of a patient with hypophosphatasia and osteoporosis treated with Romo. In our patient, Romo did not significantly impact serum alkaline phosphatase, but improved bone mineral density significantly. In conclusion, Romo is a potential treatment option for osteoporosis in patients with hypophosphatasia for whom limited alternatives exist.

Associations of Obesity and Neighborhood Factors With Urinary Stone Parameters

INTRODUCTION

Obesity is associated with kidney stone disease, but it is unknown whether this association differs by SES. This study assessed the extent to which obesity and neighborhood characteristics jointly contribute to urinary risk factors for kidney stone disease.

METHODS

This was a retrospective analysis of adult patients with kidney stone disease evaluated with 24-hour urine collection (2001-2020). Neighborhood-level socioeconomic data were obtained for a principal component analysis, which identified 3 linearly independent factors. Associations between these factors and 24-hour urine measurements were assessed using linear regression as well as groupings of 24-hour urine results using multivariable logistic regression. Finally, multiplicative interactions were assessed testing effect modification by obesity, and analyses stratified by obesity were performed. Analyses were performed in 2021.

RESULTS

In total, 1,264 patients met the study criteria. Factors retained on principal component analysis represented SES, family structure, and housing characteristics. On linear regression, there was a significant inverse correlation between SES and 24-hour urine sodium (p=0.0002). On multivariable logistic regression, obesity was associated with increased odds of multiple stone risk factors (OR=1.61; 95% CI=1.15, 2.26) and multiple dietary factors (OR=1.33; 95% CI=1.06, 1.67). No significant and consistent multiplicative interactions were observed between obesity and quartiles of neighborhood SES, family structure, or housing characteristics.

CONCLUSIONS

Obesity was associated with the presence of multiple stone risk factors and multiple dietary factors; however, the strength and magnitude of these associations did not vary significantly by neighborhood SES, family structure, and housing characteristics.

Preclinical and Clinical Evidence of Effect of Acid on Bone Health

Acid can have ill effect on bone health in the absence of frank clinical acidosis but affecting the bone mioneral matrix and bone cells via complex pathways botyh ascute;y and chronically. While the reaction of bone to an acid load is conserved in evolution and is adaptive, the capacity can be overwhelmed resulting in dire consequences. The preclinical an clincl evidence of the acdi effect on bone is very convincing and the clinical evidence in both association and interventiopn studies are also quite credible, The adverse effects of acid on bone is underappreoicated, under-investigated, and the potential benefits of alkali therapy is not generrally known.

Quality of life impact and recovery after ureteroscopy and stent insertion: insights from daily surveys in STENTS

BACKGROUND

Our objective was to describe day-to-day evolution and variations in patient-reported stent-associated symptoms (SAS) in the STudy to Enhance uNderstanding of sTent-associated Symptoms (STENTS), a prospective multicenter observational cohort study, using multiple instruments with conceptual overlap in various domains.

METHODS

In a nested cohort of the STENTS study, the initial 40 participants having unilateral ureteroscopy (URS) and stent placement underwent daily assessment of self-reported measures using the Brief Pain Inventory short form, Patient-Reported Outcome Measurement Information System measures for pain severity and pain interference, the Urinary Score of the Ureteral Stent Symptom Questionnaire, and Symptoms of Lower Urinary Tract Dysfunction Research Network Symptom Index. Pain intensity, pain interference, urinary symptoms, and bother were obtained preoperatively, daily until stent removal, and at postoperative day (POD) 30.

RESULTS

The median age was 44 years (IQR 29,58), and 53% were female. The size of the dominant stone was 7.5 mm (IQR 5,11), and 50% were located in the kidney. There was consistency among instruments assessing similar concepts. Pain intensity and urinary symptoms increased from baseline to POD 1 with apparent peaks in the first 2 days, remained elevated with stent in situ, and varied widely among individuals. Interference due to pain, and bother due to urinary symptoms, likewise demonstrated high individual variability.

CONCLUSIONS

This first study investigating daily SAS allows for a more in-depth look at the lived experience after URS and the impact on quality of life. Different instruments measuring pain intensity, pain interference, and urinary symptoms produced consistent assessments of patients' experiences. The overall daily stability of pain and urinary symptoms after URS was also marked by high patient-level variation, suggesting an opportunity to identify characteristics associated with severe SAS after URS.

Androgen Deprivation Therapy Differentially Impacts Bone and Muscle in the Short Term in Physically Active Men With Prostate Cancer

Androgen deprivation therapy (ADT) is a cornerstone of advanced prostate cancer (PCa) therapy. Its use is associated with a loss of bone mineral density (BMD) and a greater risk of falls and osteoporotic fractures. In this prospective cohort study, we examined the impact of ADT on muscle and bone strength in men initiating ADT for PCa. Participants were evaluated at three time points: immediately before (week 0), and 6 and 24 weeks after ADT initiation. Study measures included fasting blood levels (for markers of muscle and bone metabolic activity), MRI and QCT imaging (for muscle fat content, and bone density and architecture), and validated clinical tests of muscle strength and gait. Sixteen men completed all study visits. At baseline and throughout the study, participants exercised a median of four times/week, but still experienced weight gain (+2.0 kg at week 24 versus week 0, p = 0.004). Biochemically, all men sustained dramatic early and persistent reductions in sex hormones post-ADT, along with a progressive and significant increase in serum C-telopeptide of type I collagen (CTX, +84% at week 24 versus week 0). There was a trend for rise in serum sclerostin (p = 0.09) and interleukin 6 (IL-6) (p = 0.08), but no significant change in serum myostatin (p = 0.99). Volumetric BMD by QCT declined significantly at the femoral neck (-3.7% at week 24 versus week 0), particularly at the trabecular compartment. On MRI, there were no significant changes in thigh muscle fat fraction. On physical testing, men developed weaker grip strength, but experienced no worsening in lower extremity and lumbar spine muscle strength, or on functional tests of gait. In conclusion, in physically active men, ADT for 24 weeks results in a significant increase in bone resorption and reduction in BMD, but nonsignificant changes in thigh muscle quality (on imaging) or strength and gait (on functional testing). © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Disparities in Kidney Stone Disease: A Scoping Review

PURPOSE

We reviewed the available evidence regarding health disparities in kidney stone disease to identify knowledge gaps in this area.

MATERIALS AND METHODS

A literature search was conducted using PubMed®, Embase® and Scopus® limited to articles published in English from 1971 to 2020. Articles were selected based on their relevance to disparities in kidney stone disease among adults in the United States.

RESULTS

Several large epidemiological studies suggest disproportionate increases in incidence and prevalence of kidney stone disease among women as well as Black and Hispanic individuals in the United States, whereas other studies of comparable size do not report racial and ethnic demographics. Numerous articles describe disparities in imaging utilization, metabolic workup completion, analgesia, surgical intervention, stone burden at presentation, surgical complications, followup, and quality of life based on race, ethnicity, socioeconomic status and place of residence. Differences in urinary parameters based on race, ethnicity and socioeconomic status may be explained by both dietary and physiological factors. All articles assessed had substantial risk of selection bias and confounding.

CONCLUSIONS

Health disparities are present in many aspects of kidney stone disease. Further research should focus not only on characterization of these disparities but also on interventions to reduce or eliminate them.

Impact of age and renal function on urine chemistry in patients with calcium oxalate kidney stones

Nephrolithiasis is associated with an increased risk of chronic kidney disease, and its incidence varies with age. However, little is known on the combined impact of aging and declining renal function on urinary risk factors for calcium oxalate stone formation. A retrospective analysis was performed on 24-h urine collections from 993 calcium oxalate stone-forming patients. We first tested for interactions between age and creatinine clearance on various urinary determinants of calcium oxalate nephrolithiasis, and then examined their separate and combined effects in univariable and multivariable analyses adjusting for demographic and biochemical covariates. We identified significant interactions between age and creatinine clearance in predicting 24-h urine pH, calcium, and citrate. In view of the small number of stone formers with low creatinine clearance, we limited further regression analyses to patients with creatinine clearance ≥ 60 mL/min. In multivariable analyses, urine citrate, oxalate, and total volume were positively correlated with age, whereas urine pH, citrate, calcium, oxalate, total volume, and RSR of calcium oxalate all significantly decreased with lower creatinine clearance. A decrease in creatinine clearance from 120 to 60 mL/min was associated with clinically significant decreases in the daily excretion rate of citrate (by 188 mg/day), calcium (by 33 mg/day), and oxalate (by 4 mg/day), and in RSR calcium oxalate (by 1.84). Age and creatinine clearance are significant and independent predictors of several urinary determinants of calcium oxalate nephrolithiasis. The impacts of aging and declining renal function should be considered during the management of calcium oxalate stone-forming patients.

Study to Enhance Understanding of Stent-Associated Symptoms: Rationale and Study Design

Background: Ureteral stents are commonly employed after ureteroscopy to treat urinary stone disease, but the devices impose a substantial burden of stent-associated symptoms (SAS), including pain and urinary side effects. The NIDDK (National Institute of Diabetes and Digestive and Kidney Diseases) Urinary Stone Disease Research Network sought to develop greater understanding of SAS causes and severity among individuals treated ureteroscopically for ureteral or renal stones. Materials and Methods: We designed a prospective, observational cohort study comprising adolescents and adults undergoing ureteroscopic intervention for ureteral or renal stones. Participants will undergo detailed symptom assessment using validated questionnaires, a psychosocial assessment, and detailed collection of clinical and operative data. Quantitative sensory testing will be utilized to assess pain sensitization. In addition, a small cohort (∼40 individuals) will participate in semi-structured interviews to develop more granular information regarding their stent symptoms and experience. Biospecimens (blood and urine) will be collected for future research. Results: The Study to Enhance Understanding of sTent-associated Symptoms (STENTS) enrolled its first participant in March 2019 and completed nested qualitative cohort follow-up in August 2019. After a planned pause, enrollment for the main study cohort resumed in September 2019 and is expected to be completed in 2021. Conclusion: STENTS is expected to provide important insights into the mechanisms and risk factors for severe ureteral SAS after ureteroscopy. These insights will generate future investigations to mitigate the burden of SAS among individuals with urinary stone disease.

Prevention of Urinary Stones With Hydration (PUSH): Design and Rationale of a Clinical Trial

RATIONALE & OBJECTIVE

Although maintaining high fluid intake is an effective low-risk intervention for the secondary prevention of urinary stone disease, many patients with stones do not increase their fluid intake.

STUDY DESIGN

We describe the rationale and design of the Prevention of Urinary Stones With Hydration (PUSH) Study, a randomized trial of a multicomponent behavioral intervention program to increase and maintain high fluid intake. Participants are randomly assigned (1:1 ratio) to the intervention or control arm. The target sample size is 1,642 participants.

SETTING & PARTICIPANTS

Adults and adolescents 12 years and older with a symptomatic stone history and low urine volume are eligible. Exclusion criteria include infectious or monogenic causes of urinary stone disease and comorbid conditions precluding increased fluid intake.

INTERVENTIONS

All participants receive usual care and a smart water bottle with smartphone application. Participants in the intervention arm receive a fluid intake prescription and an adaptive program of behavioral interventions, including financial incentives, structured problem solving, and other automated adherence interventions. Control arm participants receive guideline-based fluid instructions.

OUTCOMES

The primary end point is recurrence of a symptomatic stone during 24 months of follow-up. Secondary end points include changes in radiographic stone burden, 24-hour urine output, and urinary symptoms.

LIMITATIONS

Periodic 24-hour urine volumes may not fully reflect daily behavior.

CONCLUSIONS

With its highly novel features, the PUSH Study will address an important health care problem.

FUNDING

National Institute of Diabetes and Digestive and Kidney Diseases.

TRIAL REGISTRATION

Registered at ClinicalTrials.gov with study number NCT03244189.

What Predicts Recurrent Kidney Stone after Parathyroidectomy in Patients with Primary Hyperparathyroidism?

BACKGROUND

Some, but not all, patients with primary hyperparathyroidism (PHPT) and kidney stone disease (KSD) are cured of their nephrolithiasis after parathyroidectomy. The goal of this study was to identify risk factors for recurrent KSD despite successful parathyroidectomy in known stone formers with PHPT.

STUDY DESIGN

We conducted a single-center retrospective review of patients presenting to urology clinic with KSD between January 2008 and July 2018, who were diagnosed with concurrent PHPT, and underwent definitive parathyroidectomy. Laboratory testing for serum calcium, PTH (parathyroid hormone), phosphorus and 25-OH-vitamin D, and 24-hour urine studies for volume, pH, calcium, citrate, oxalate, uric acid, sodium, and creatinine was performed pre- and post-parathyroidectomy. Stone recurrence was determined on routine diagnostic imaging or by symptomatic KSD.

RESULTS

Mean age at parathyroidectomy was 57 ± 14 years. Pre-parathyroidectomy, mean serum calcium, 24-hour urine calcium, and PTH were 10.6 ± 0.5 mg/dL, 378 ± 209 mg/day, and 114 ± 97 pg/mL, respectively. Twenty-six of 69 patients (38%) had multigland parathyroid disease. After parathyroidectomy, serum calcium and PTH levels normalized in 69 of 69 and 62 of 69 patients, respectively. However, 37 of 69 patients (54%) had persistent hypercalciuria postoperatively, and 16 of 69 (23%) had recurrent KSD, on average, 2.0 ± 1.6 years after parathyroidectomy. Patients with recurrent KSD post-parathyroidectomy were significantly younger compared with patients without recurrent KSD (51 ± 15 vs 60 ± 13 years, p = 0.02). In a logistic regression model, younger age remains a strong predictive factor for recurrent KSD.

CONCLUSIONS

Nearly one-quarter of PHPT patients with KSD who undergo successful parathyroidectomy present with recurrent KSD despite normalization of serum calcium, and more than half exhibit persistent calciuria. These patients were younger and may require closer monitoring for stone recurrence after successful parathyroidectomy. Further studies are needed to better identify the etiology of KSD post-parathyroidectomy.

Citrate therapy for calcium phosphate stones

PURPOSE OF REVIEW

Calcium phosphate (CaP) stones represent an increasingly encountered form of recurrent nephrolithiasis, but current prophylactic medical regimens are suboptimal. Although hypocitraturia is a well-described risk factor for CaP stones, strategies that enhance citrate excretion have not consistently been effective at reducing CaP saturation and stone recurrence. This review summarizes the role of citrate therapy in CaP nephrolithiasis.

RECENT FINDINGS

Citrate in urine inhibits CaP stone formation through multiple mechanisms, including the formation of soluble citrate-calcium complexes, and inhibition of CaP nucleation, crystal growth and crystal aggregation. Recent in-vitro studies demonstrate that citrate delays CaP crystal growth through distinct inhibitory mechanisms that depend on supersaturation and citrate concentration. The impact of pharmacological provision of citrate on CaP saturation depends on the accompanying cation: Potassium citrate imparts a significant alkali load that enhances citraturia and reduces calciuria, but could worsen urine pH elevation. Conversely, citric acid administration results in minimal citraturia and alteration in CaP saturation.

SUMMARY

Citrate, starting at very low urinary concentrations, can significantly retard CaP crystal growth in vitro through diverse mechanisms. Clinically, the net impact on CaP stone formation of providing an alkali load during pharmacological delivery of citrate into the urinary environment remains to be determined.

The Differential Effects of Human Immunodeficiency Virus and Hepatitis C Virus on Bone Microarchitecture and Fracture Risk

Background

Human immunodeficiency virus (HIV)/hepatitis C virus (HCV)-coinfected individuals have a significantly greater osteoporotic fracture risk than HIV-monoinfected persons, despite the fact that HIV/HCV coinfection has not been associated with lower bone mineral density (BMD) than HIV or HCV alone. To evaluate if changes in bone microarchitecture, measured by trabecular bone score (TBS), could explain these differences, we performed a prospective, cross-sectional cohort study of virologically suppressed HIV-infected subjects, untreated HCV-infected subjects, HIV/HCV-coinfected subjects, and uninfected controls.

Methods

We enrolled 532 male subjects: 57 HIV/HCV coinfected, 174 HIV infected, 123 HCV infected, and 178 controls. We conducted analysis of covariance comparing BMD and TBS between groups, controlling for age, race, body mass index, and smoking. We used linear regression to evaluate predictors of BMD and TBS and evaluated the effects of severity of HCV infection and tenofovir disoproxil fumarate use.

Results

Despite both infections being associated with decreased BMD, only HCV, but not HIV, was associated with lower TBS score. Also, HIV/HCV-coinfected subjects had lower TBS scores than HIV-monoinfected, HCV-monoinfected, and uninfected subjects. Neither the use of TDF or HCV viremia nor the severity of HCV liver disease was associated with lower TBS.

Conclusions

HCV infection is associated with microarchitectural changes at the lumbar spine as assessed by the low TBS score, suggesting that microstructural abnormalities underlie some of the higher fracture risk in HCV infection. TBS might improve fracture risk prediction in HCV infection.

Association of serum magnesium with all-cause mortality in patients with and without chronic kidney disease in the Dallas Heart Study

Background

Low serum magnesium (SMg) has been linked to increased mortality and cardiovascular disease (CVD) in the general population. We examined whether this association is similar in participants with versus without prevalent chronic kidney disease (CKD) in the multiethnic Dallas Heart Study (DHS) cohort.

Methods

SMg was analyzed as a continuous variable and divided into tertiles. Study outcomes were all-cause death, cardiovascular (CV) death or event, and CVD surrogate markers, evaluated using multivariable Cox regression models adjusted for demographics, comorbidity, anthropometric and biochemical parameters including albumin, phosphorus and parathyroid hormone, and diuretic use. Median follow-up was 12.3 years (11.9-12.8, 25th percentile-75th percentile).

Results

Among 3551 participants, 306 (8.6%) had prevalent CKD. Mean SMg was 2.08 ± 0.19 mg/dL (0.85 ± 0.08 mM, mean ± SD) in the CKD and 2.07 ± 0.18 mg/dL (0.85 ± 0.07 mM) in the non-CKD subgroups. During the follow-up period, 329 all-cause deaths and 306 CV deaths or events occurred. In a fully adjusted model, every 0.2 mg/dL decrease in SMg was associated with ∼20-40% increased hazard for all-cause death in both CKD and non-CKD subgroups. In CKD participants, the lowest SMg tertile was also independently associated with all-cause death (adjusted hazard ratio 2.31; 95% confidence interval 1.23-4.36 versus 1.15; 0.55-2.41; for low versus high tertile, respectively).

Conclusions

Low SMg levels (1.4-1.9 mg/dL; 0.58-0.78 mM) were independently associated with all-cause death in patients with prevalent CKD in the DHS cohort. Randomized clinical trials are important to determine whether Mg supplementation affects survival in CKD patients.

Association Between Bone Mineral Density and Depressive Symptoms in a Population-Based Sample

OBJECTIVE

This analysis was conducted to determine the relationship between bone mineral density (BMD) and depressive symptoms in a population-based cohort.

METHODS

Data were extracted from the second phase of the Dallas Heart Study (DHS-2), a large, multiethnic population sample in Dallas County, Texas, from September 1, 2007, to December 31, 2009. Depressive symptom severity was measured with the 16-item Quick Inventory of Depressive Symptomatology-Self Report (QIDS-SR₁₆), which is derived from DSM-IV major depressive disorder criteria. BMD was measured using dual-energy x-ray absorptiometry. Multiple linear regressions examined the relationship between QIDS-SR₁₆ score and BMD controlling for age, body mass index, sex, ethnicity, smoking status, alcohol use status, serum 25-hydroxyvitamin D concentration, antidepressant use, and physical activity as measured by total vigorous and moderate metabolic equivalents. Subgroup analyses explored differences related to age.

RESULTS

QIDS-SR₁₆ score was not a significant predictor of either lumbar spine or total hip T-score (β = -0.01, P = .61 and β = -0.02, P = .39) in the overall population (n = 2,285). There was a significant negative interaction term between age and QIDS-SR₁₆ group (β = -0.01, P = .01). In participants aged 60 years or older (n = 465), QIDS-SR₁₆ score was a significant predictor of BMD at the lumbar spine and total hip (β = -0.14, P = .003 and β = -0.12, P = .006, respectively).

CONCLUSIONS

QIDS-SR₁₆ score did not significantly predict BMD in the overall DHS-2 sample. There was, however, a significant association observed in participants aged ≥ 60 years. Results suggest that diagnosis and treatment of depressive symptoms may be of clinical importance in older individuals, a subgroup at high risk for osteoporosis and fractures.

CT bone density analysis of low-impact proximal femur fractures using Hounsfield units

AIM

To quantify and compare changes in bone mineral density (BMD) via CT analysis in patients with and without spontaneous femoral fractures.

MATERIALS AND METHODS

Consecutive series of patients with CT imaging for spontaneous femoral fractures were compared to the age and gender matched controls. Bone density fixed region of interest measurements were obtained at the site of the fracture, proximally at the femoral head, and distally at the lesser trochanter in fracture patients and controls. Inter- and intrapatient comparisons were performed, including Chi-square and t-test analyses.

RESULTS

24 spontaneous fractures and 25 controls were analyzed with no significant differences in mean age, gender, or body mass index. There were differences in the bone density between the fracture and contralateral non-fracture sides at (p = 0.0001) and distal (p < 0.0001) to the fracture. Proximal and distal bone density differences existed between case fracture and control non-fracture sites (p < 0.0001, p = 0.0001), and between the case non-fracture and control non-fracture sites (p < 0.0001, p < 0.0001). The reliability for measurements was good to excellent proximally (ICC = 0.63-0.87), moderate to excellent at the fracture site (ICC = 0.43-0.78), and fair to good distal (ICC = 0.24-0.68) to the fracture site.

CONCLUSION

Patients with spontaneous femoral fractures exhibit lower bone density than the asymptomatic controls. Bone insufficiency is best demonstrated proximal or distal to, rather than at the fracture site.

Net Acid Excretion and Urinary Organic Anions in Idiopathic Uric Acid Nephrolithiasis

BACKGROUND AND OBJECTIVES

Idiopathic uric acid nephrolithiasis, which is closely associated with obesity and the metabolic syndrome, is increasing in prevalence. Unduly acidic urine pH, the quintessential pathophysiologic feature of this disease, is in part explained by inadequate excretion of the principal urinary buffer ammonium. The role of net acid excretion in the pathogenesis of uric acid nephrolithiasis is incompletely understood.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We compared acid-base parameters of patients with idiopathic uric acid nephrolithiasis with matched control subjects under controlled diets in an inpatient metabolic unit. Measurements included fasting blood and 24-hour urine chemistries and 24-hour urine metabolomic analysis. Comparisons between groups included analysis of covariance models controlling for urine pH or body mass index.

RESULTS

Subjects with idiopathic uric acid nephrolithiasis had lower urine pH (5.5 versus 5.9; P<0.001) and higher net acid excretion (60 versus 43 mEq/24 h; P<0.001), with the excess H+ carried by nonammonium buffers. In all subjects, there was a positive relationship of net acid excretion with higher body mass index in spite of strictly controlled equivalent dietary acid intake. This relationship was most evident among control subjects (r=0.36; P=0.03). It was attenuated in patients with idiopathic uric acid nephrolithiasis whose net acid excretion remained fixedly high and ammonium excretion remained low relative to net acid excretion, resulting in low urine pH over a wide body mass index range. Urinary metabolomics was performed to attempt to identify excess organic acids presented to the kidney in idiopathic uric acid nephrolithiasis. Among the tricarboxylic acid cycle intermediates and amino acid and lipid metabolites analyzed, 26 organic anions with acid dissociation constants values in the range of urine pH showed greater protonation. However, protons carried by the identified organic acids did not entirely account for the higher titratable acidity seen in idiopathic uric acid nephrolithiasis.

CONCLUSIONS

Higher acid load to the kidney, resulting in higher urinary net acid excretion, is an important factor in the pathogenesis of idiopathic uric acid nephrolithiasis.

Low serum magnesium is associated with faster decline in kidney function: the Dallas Heart Study experience

Hypomagnesemia associates with inflammation and risk of diabetes and hypertension, which may contribute to kidney function decline. We hypothesized that low serum magnesium (SMg) levels independently associate with a significant decline in estimated glomerular filtration rate (eGFR). We analyzed SMg levels in 2056 participants from the Dallas Heart Study, a longitudinal, population-based, multiethnic, cohort study involving residents of Dallas County, Texas, USA. The primary study outcome was the change in eGFR using multivariable linear regression models adjusted for demographics, anthropometric and biochemical parameters, medications, C reactive protein levels, prevalent hypertension and diabetes. During a median follow-up of 7.0 years (25th, 75th percentile: 6.5, 7.6), the median decrease in eGFR was -0.71 (25th, 75th percentile: -2.43, +0.68) mL/min/1.73 m² per year in the entire cohort. In a fully adjusted model, the lowest SMg quintile (≤1.9 mg/dL or ≤0.8 mM) was associated with a -0.50 mL/min/1.73 m² per year drop in eGFR (95% CI -0.95 to -0.05; p=0.028) compared with the highest SMg quintile (≥2.3 mg/dL or ≥1.0 mM). Every 0.2 mg/dL (0.08 mM) decrease in SMg was associated with an eGFR decline of -0.23 mL/min/1.73 m² per year (95% CI -0.38 to -0.08; p=0.003), a decline that was more pronounced in participants with prevalent diabetes compared with patients without diabetes (-0.51 vs -0.18 mL/min/1.73 m² per year, respectively). In conclusion, low SMg was independently associated with eGFR decline. Further studies are needed to determine whether Mg repletion can ameliorate inflammation, lower blood pressure and serum glucose and ultimately prevent or retard kidney function decline.

Increased production and reduced urinary buffering of acid in uric acid stone formers is ameliorated by pioglitazone

Idiopathic uric acid nephrolithiasis is characterized by an overly acidic urine pH caused by the combination of increased acid production and inadequate buffering of urinary protons by ammonia. A large proportion of uric acid stone formers exhibit features of the metabolic syndrome. We previously demonstrated that thiazolidinediones improved the urinary biochemical profile in an animal model of the metabolic syndrome. In this proof-of-concept study, we examined whether the thiazolidinedione pioglitazone can also ameliorate the overly acidic urine in uric acid stone formers. Thirty-six adults with idiopathic uric acid nephrolithiasis were randomized to pioglitazone 30 mg/day or matching placebo for 24 weeks. At baseline and study end, participants underwent collection of blood and 24-hour urine in an inpatient research unit while consuming a fixed metabolic diet, followed by assessment of the ammoniagenic response to an acute oral acid load. Twenty-eight participants completed the study. Pioglitazone treatment improved features of the metabolic syndrome. Pioglitazone also reduced net acid excretion and increased urine pH (5.37 to 5.59), the proportion of net acid excreted as ammonium, and ammonium excretion in response to an acute acid load, whereas these parameters were unchanged with placebo. Treatment of patients with idiopathic uric acid nephrolithiasis with pioglitazone for 24 weeks led to a reduction in the acid load presented to the kidney and a more robust ammoniagenesis and ammonium excretion, resulting in significantly higher urine pH. Future studies should consider the impact of this targeted therapy on uric acid stone formation.

Impact of Potassium Citrate vs Citric Acid on Urinary Stone Risk in Calcium Phosphate Stone Formers

PURPOSE

To our knowledge no medication has been shown to be effective for preventing recurrent calcium phosphate urinary stones. Potassium citrate may protect against calcium phosphate stones by enhancing urine citrate excretion and lowering urine calcium but it raises urine pH, which increases calcium phosphate saturation and may negate the beneficial effects. Citric acid can potentially raise urine citrate but not pH and, thus, it may be a useful countermeasure against calcium phosphate stones. We assessed whether these 2 agents could significantly alter urine composition and reduce calcium phosphate saturation.

MATERIALS AND METHODS

In a crossover metabolic study 13 recurrent calcium phosphate stone formers without hypercalciuria were evaluated at the end of 3, 1-week study phases during which they consumed a fixed metabolic diet and received assigned study medications, including citric acid 30 mEq twice daily, potassium citrate 20 mEq twice daily or matching placebo. We collected 24-hour urine specimens to perform urine chemistry studies and calculate calcium phosphate saturation indexes.

RESULTS

Urine parameters did not significantly differ between the citric acid and placebo phases. Potassium citrate significantly increased urine pH, potassium and citrate compared to citric acid and placebo (p <0.01) with a trend toward lower urine calcium (p = 0.062). Brushite saturation was increased by potassium citrate when calculated by the relative supersaturation ratio but not by the saturation index.

CONCLUSIONS

Citric acid at a dose of 60 mEq per day did not significantly alter urine composition in calcium phosphate stone formers. The long-term impact of potassium citrate on calcium phosphate stone recurrence needs to be studied further.

Effects of pharmacological reversal of hyperuricemia on features of the metabolic syndrome in patients with gouty arthritis

Hyperuricemia has been associated in epidemiological studies with the development of obesity, hypertension, insulin resistance and type 2 diabetes. Nevertheless, it remains unclear whether lowering of serum uric acid (UA) alters any of the features of the metabolic syndrome. In this prospective study (ClinicalTrials.gov identifier: NCT01654276), 24 patients with gouty arthritis and hyperuricemia were treated for 6 months with the xanthine oxidase inhibitor febuxostat to lower serum UA to <6 mg/dL. Measurements of 24 hours ambulatory blood pressure (ABP) and serum and urine markers of the metabolic syndrome were measured at baseline and at the end of 6 months of febuxostat. The study population consisted of 18 men and 6 women, 18 of which completed the baseline and 6 months visits. Serum UA decreased significantly from 8.7±1.5 mg/dL at baseline to 4.4±1.1 mg/dL at 6 months (P<0.0001). During that time frame, there was no significant change in body mass index, systolic or diastolic blood pressure measured by 24 hours ABP monitor, serum glucose, insulin or homeostatic model assessment for insulin resistance, serum total and high-density lipoprotein-cholesterol, serum triglycerides or urine pH (P>0.05 for all). There was no correlation between parameters of the metabolic syndrome and the decline in serum UA or serum UA achieved at study end. In conclusion, in patients with gouty arthritis, UA lowering with febuxostat below 6 mg/dL had no significant impact on features of the metabolic syndrome.

Impact of pioglitazone on bone mineral density and bone marrow fat content

Pioglitazone use is associated with an increased risk of fractures. In this randomized, placebo-controlled study, pioglitazone use for 12 months was associated with a significant increase in bone marrow fat content at the femoral neck, accompanied by a significant decrease in total hip bone mineral density. The change in bone marrow fat with pioglitazone use was predominantly observed in female vs. male participants.

INTRODUCTION

Use of the insulin sensitizer pioglitazone is associated with greater fracture incidence, although the underlying mechanisms are incompletely understood. This study aimed to assess the effect of pioglitazone treatment on femoral neck bone marrow (BM) fat content and on bone mineral density (BMD), and to establish if any correlation exists between the changes in these parameters.

METHODS

In this double-blind placebo-controlled clinical trial, 42 obese volunteers with metabolic syndrome were randomized to pioglitazone (45 mg/day) or matching placebo for 1 year. The following measurements were conducted at baseline and during the treatment: liver, pancreas, and femoral neck BM fat content (by magnetic resonance spectroscopy), BMD by DXA, abdominal subcutaneous and visceral fat, and beta-cell function and insulin sensitivity.

RESULTS

Results were available for 37 subjects who completed the baseline and 1-year evaluations. At 12 months, BM fat increased with pioglitazone (absolute change, +4.1%, p = 0.03), whereas BM fat content in the placebo group decreased non-significantly (-3.1%, p = 0.08) (p = 0.007 for the pioglitazone-placebo response difference). Total hip BMD declined in the pioglitazone group (-1.4%) and increased by 0.8% in the placebo group (p = 0.03 between groups). The change in total hip BMD was inversely and significantly correlated with the change in BM fat content (Spearman rho = -0.56, p = 0.01) in the pioglitazone group, but not within the placebo group (rho = -0.29, p = 0.24). Changes in BM fat with pioglitazone were predominantly observed in female vs. male subjects.

CONCLUSIONS

Pioglitazone use for 12 months compared with placebo is associated with significant increase in BM fat content at the femoral neck, accompanied by a small but significant decrease in total hip BMD.

Skeletal Fluorosis Due to Fluorocarbon Inhalation from an Air Dust Cleaner

Skeletal fluorosis (SF) is an osteosclerotic metabolic bone disorder caused by excessive ingestion or inhalation of fluoride. SF is extremely rare in developed countries. We report a case of SF due to inhalational abuse from a fluoride-containing air dust cleaner. A 33-year-old man with no past medical history presented with progressively worsening low back pain for 2 years. Physical examination was notable for loss of lumbar lordosis and tenderness over the lumbar spine. Radiographs were notable for uniform generalized osteosclerosis in the long bones, entire spine, rib cage, and pelvic bones, and loss of the normal lumbar curvature. DXA scan showed Z-scores of +10.7 at the lumbar spine, +6.5 at the total hip, and +1.0 at the 1/3 radius. Laboratory studies were notable for elevated serum alkaline phosphatase (334 U/L, ref: 40-129 U/L) compared to a normal value 3 years prior, suggesting acquired osteosclerosis. Serum fluoride concentration returned elevated (2.8 mg/L, ref: 0.0-0.2 mg/L). Initially, the source of fluoride excess could not be identified. At a follow-up visit, he was found inhaling from a can of an air duster hidden in an inner pocket. He admitted "huffing" 2-7 cans weekly from a fluorocarbon-containing air dust cleaner for the past 3 years to achieve a euphoric feeling, explaining the source of his SF. Fluoride inhalation can be a potential source for SF, and should be suspected in patients with acquired osteosclerosis, as inhalant abuse is increasingly practiced in many countries.

Longitudinal changes in serum 25-hydroxyvitamin D in the Dallas Heart Study

CONTEXT

While the prevalence of vitamin D deficiency is well described in various populations, limited data are available regarding longitudinal variation in serum 25-hydroxyvitamin D concentrations.

OBJECTIVES

To evaluate the temporal trends in serum 25(OH)D, prevalence of vitamin D deficiency and factors influencing these trends.

PARTICIPANTS, DESIGN AND SETTING

Adults enrolled in the Dallas Heart Study, a longitudinal, probability-based, multiethnic, population study in Dallas, Texas, USA.

MAIN OUTCOME MEASURES

Prevalence of vitamin D deficiency and predictors of change in serum 25(OH)D.

RESULTS

A total of 2045 participants had serum 25(OH)D measured on two occasions (2000-2002 and 2007-2009) at a median interval of 7 years. Serum 25(OH)D decreased (42.7-39.4 nmol/L, P<.001) and the prevalence of vitamin D deficiency [25(OH)D <50 nmol/L] increased significantly (60.6%-66.4%, P<.0001) despite vitamin D supplementation increasing over the interval (7.2%-23.0%; P<.0001). In a multivariable model adjusting for sex, race, BMI, age, season of blood draw, smoking and exercise, a greater decline in serum 25(OH)D was noted in men compared with women (-8.0 vs -3.5 nmol/L, P<.0001), in participants of Hispanic ethnicity vs White and Black ethnicity (P<.0001), in nonobese vs obese participants (-7.2 vs -4.0 nmol/L, P=.005) and in nonusers vs users of vitamin D supplements (-5.7 vs -1.7 nmol/L, P=.032).

CONCLUSIONS

Despite increased vitamin D supplementation, serum 25(OH)D decreased in an ethnically diverse cohort of Dallas County residents between 2000-2002 and 2007-2009. Features most predictive of a decline in serum 25(OH)D include male sex, Hispanic ethnicity and weight gain.

Glucocorticoid-responsive lymphocytic parathyroiditis and hypocalciuric hypercalcemia due to autoantibodies against the calcium-sensing receptor: a case report and literature review

OBJECTIVE

Autoimmune lymphocytic parathyroiditis and acquired hypocalciuric hypercalcemia associated with autoantibodies against the calcium-sensing receptor (anti-CaSR) are rare and poorly understood conditions. Here, we describe a patient with acquired parathyroid hormone (PTH)-dependent hypercalcemia with associated hypocalciuria, found to have true lymphocytic parathyroiditis on histopathology, and circulating anti-CaSR antibodies in serum.

DESIGN AND METHODS

A 64-year-old woman was referred to our clinic for persistent hypercalcemia after a subtotal parathyroidectomy. She was normocalcemic until the age of 63 years when she was diagnosed with primary hyperparathyroidism. She underwent subtotal parathyroidectomy with appropriate intraoperative PTH decline. Two weeks post-parathyroidectomy, she presented with persistent hypercalcemia and hyperparathyroidism. Urine studies revealed an inappropriately low 24-h urine calcium (Ca)/creatinine clearance ratio. Surgical pathology was consistent with true lymphocytic parathyroiditis with lymphoid follicles. The presence of circulating anti-CaSR antibodies was detected by immunoprecipitation of CaSR by the patient's serum. After a 4-week course of prednisone, serum Ca and PTH normalized, and her anti-CaSR titers declined. She remains normocalcemic 10 months after the discontinuation of glucocorticoid therapy. We present this patient in the context of the relevant published literature on lymphocytic parathyroiditis and acquired hypocalciuric hypercalcemia related to anti-CaSR antibodies.

CONCLUSIONS

Autoimmune lymphocytic parathyroiditis and acquired hypocalciuric hypercalcemia associated with anti-CaSR antibodies is a very rare yet important condition to be considered in a patient with acquired PTH-dependent hypercalcemia with inappropriate hypocalciuria. Although subtotal parathyroidectomy is unlikely to correct the hypercalcemia, this entity may respond to a short course of prednisone therapy.

Effect of acute hyperinsulinemia on magnesium homeostasis in humans

BACKGROUND

Insulin may influence magnesium homeostasis through multiple mechanisms. Acutely, it stimulates the shift of magnesium from plasma into red blood cells and platelets, and in vitro, it stimulates the activity of the TRPM6 channel, a key regulator of renal magnesium reabsorption. We investigated the impact of hyperinsulinemia on magnesium handling in participants with a wide range of insulin sensitivity.

METHOD

Forty-seven participants were recruited, including 34 nondiabetic controls and 13 with type 2 diabetes mellitus. After stabilization under fixed metabolic diet, participants underwent hyperinsulinemic-euglycemic clamp. Serum and urine samples were collected before and during hyperinsulinemia. Change in serum magnesium, urinary magnesium to creatinine (Mg²⁺ :Cr) ratio, fractional excretion of urinary magnesium (FEMg²⁺ ), and estimated transcellular shift of magnesium were compared before and during hyperinsulinemia.

RESULTS

Hyperinsulinemia led to a small but statistically significant decrease in serum magnesium, and to a shift of magnesium into the intracellular compartment. Hyperinsulinemia did not significantly alter urinary magnesium to creatinine ratio or fractional excretion of urinary magnesium in the overall population, although a small but statistically significant decline in these parameters occurred in participants with diabetes. There was no significant correlation between change in fractional excretion of urinary magnesium and body mass index or insulin sensitivity measured as glucose disposal rate.

CONCLUSIONS

In human participants, acute hyperinsulinemia stimulates the shift of magnesium into cells with minimal alteration in renal magnesium reabsorption, except in diabetic patients who experienced a small decline in fractional excretion of urinary magnesium. The magnitude of magnesium shift into the intracellular compartment in response to insulin does not correlate with that of insulin-stimulated glucose entry into cells.

Temporal Changes in Kidney Stone Composition and in Risk Factors Predisposing to Stone Formation

PURPOSE

The prevalence of kidney stones has increased globally in recent decades. However, studies investigating the association between temporal changes in the risk of stone formation and stone types are scarce. We investigated temporal changes in stone composition, and demographic, serum and urinary parameters of kidney stone formers from 1980 to 2015.

MATERIALS AND METHODS

We retrospectively analyzed the records of 1,516 patients diagnosed with either calcium or uric acid stones at an initial visit to a university kidney stone clinic from 1980 to 2015.

RESULTS

From 1980 to 2015, the proportion of uric acid stones in all stone formers increased from 7% to 14%. While age and body mass index increased with time in both uric acid and calcium stone formers, uric acid stone formers were consistently older and had a higher body mass index and lower urinary pH than calcium stone formers. The proportion of females with stones has increased over time but the increase in female gender was more prominent among calcium stone formers. Urinary pH, phosphorus, oxalate and sodium increased with time in calcium stone formers but remained unchanged in uric acid stone formers. After accounting for various parameters of stone risk, the strongest clinical discriminant of uric acid vs calcium stones was urinary pH. Limitations of this study include the retrospective single center design and the available number of patients with stone analysis.

CONCLUSIONS

From 1980 to 2015, the proportion of uric acid stones increased significantly. With time, there were proportionately more female calcium stone formers but not uric acid stone formers. Urinary pH is the most prominent factor distinguishing uric acid from calcium stones.

Determinants of change in bone mineral density and fracture risk during bisphosphonate holiday

In a retrospective analysis of 208 osteoporotic patients followed during a bisphosphonate holiday, lower body weight and risedronate use were associated with a more rapid decline in bone mineral density during the bisphosphonate holiday, while bone mineral density (BMD) trends were similar in patients who sustained vs. did not sustain a fracture.

INTRODUCTION

A drug holiday has been suggested for some bisphosphonate-treated patients with osteoporosis to minimize potential side effects from prolonged use. However, there is limited information on the evolution of BMD during a bisphosphonate holiday. Our study analyzed the longitudinal course of BMD following bisphosphonate discontinuation and assessed its determinants.

METHODS

Retrospective single-center cohort study of osteoporosis patients treated with alendronate or risedronate for at least 2 years and then discontinued their bisphosphonate for a drug holiday. Patients were stratified by bisphosphonate type and by fracture occurrence during drug holiday.

RESULTS

A total of 208 patients were included in this analysis (87.5 % female). At the time of bisphosphonate cessation, mean ± SD age was 66.9 ± 8.9 years and BMI 24.5 ± 4.4 kg/m(2). Duration of bisphosphonate treatment was 5.2 ± 2.3 years, and follow-up during holiday was 3.3 ± 1.7 years. During the first 2 years of the holiday, BMD remained stable at the lumbar spine and femoral neck, but declined significantly at the total hip. BMD declined significantly at all sites thereafter. Significant predictors of BMD decline during bisphosphonate holiday included lower BMI at the start of the holiday and change in body weight during the holiday. BMD decline was more pronounced in former risedronate compared to former alendronate users. BMD trends were similar in patients who sustained vs. did not sustain a fracture during the holiday.

CONCLUSIONS

BMD at the total hip declines significantly within 1 year of bisphosphonate discontinuation, particularly in lean patients. Additional studies are needed to identify predictors of fracture incidence during a bisphosphonate holiday.

Vitamin-D status and mineral metabolism in two ethnic populations with sarcoidosis

Vitamin-D insufficiency and sarcoidosis are more common and severe in African Americans (AA) than Caucasians. In sarcoidosis, substrate-dependent extrarenal 1,25-dihydroxyvitamin-D (1,25-(OH)2D) production is thought to contribute to hypercalciuria and hypercalcemia, and vitamin-D repletion is often avoided. However, the anti-inflammatory properties of vitamin-D may also be beneficial. We prospectively examined serum vitamin-D levels, calcium balance, and the effects of vitamin-D repletion in 86 AA and Caucasian patients with biopsy-proven active sarcoidosis from the USA (US) and Italy (IT) in university-affiliated outpatient clinics. Clinical features, pulmonary function, and calciotropic hormones were measured. 16 patients with vitamin-D deficiency and normal serum ionized calcium (Ca(2+)) were treated with oral ergocalciferol (50,000 IU/week) for 12 weeks. Baseline mineral parameters were similar in US (93% AA) and IT (95% Caucasian) patients irrespective of glucocorticoid treatment. Pulmonary dysfunction was less pronounced in IT patients. Nephrolithiasis (in 11% US, 17% IT patients) was associated with higher urinary calcium excretion. Vitamin-D deficiency was not more prevalent in patients compared to the respective general populations. As serum 25-hydroxyvitamin-D (25-OHD) rose postrepletion, serum 1,25-(OH)2D, γ-globulins, and the previously elevated angiotensin converting enzyme (ACE) levels declined. Asymptomatic reversible increases in Ca(2+) or urinary calcium/creatinine (Ca/Cr) developed in three patients during repletion. In conclusion, Caucasian and AA patients show similar calcium and vitamin D profiles. The higher prevalence of hypercalciuria and nephrolithiasis in sarcoidosis is unrelated to endogenous vitamin-D levels. Vitamin-D repletion in sarcoidosis is generally safe, although calcium balance should be monitored. A hypothesis that 25-OHD repletion suppresses granulomatous immune activity is provided.

Relationship between serum uric Acid and bone mineral density in the general population and in rats with experimental hyperuricemia

Higher serum uric acid concentrations have been associated with higher bone mineral density (BMD) in observational studies of older men and perimenopausal or postmenopausal women, prompting speculation of a potential protective effect of uric acid on bone. Whether this relationship is present in the general population has not been examined and there is no data to support causality. We conducted a cross-sectional analysis of a probability sample of the U.S.

POPULATION

Demographic data, dietary intake, lifestyle risk factors and physical activity assessment data, serum biochemistry including serum uric acid, and BMD were obtained from 6759 National Health and Nutrition Examination Survey (NHANES; 2005-2010) participants over 30 years of age. In unadjusted analyses, higher serum uric acid levels were associated with higher BMD at the femoral neck, total hip, and lumbar spine in men, premenopausal women, and postmenopausal women not treated with estrogen. However, these associations were no longer statistically significant after adjustment for potential confounders, including age, body mass index (BMI), black race, alcohol consumption, estimated glomerular filtration rate (eGFR), serum alkaline phosphatase, and C-reactive protein (CRP). This is in contradistinction to some prevailing conclusions in the literature. To further examine the causal effect of higher serum uric acid on skeletal health, including biomechanical properties that are not measurable in humans, we used an established rat model of inducible mild hyperuricemia. There were no differences in BMD, bone volume density, and bone biomechanical properties between hyperuricemic rats and normouricemic control animals. Taken together, our data do not support the hypothesis that higher serum uric acid has protective effects on bone health.

Salt and nephrolithiasis

Dietary sodium chloride intake is nowadays globally known as one of the major threats for cardiovascular health. However, there is also important evidence that it may influence idiopathic calcium nephrolithiasis onset and recurrence. Higher salt intake has been associated with hypercalciuria and hypocitraturia, which are major risk factors for calcium stone formation. Dietary salt restriction can be an effective means for secondary prevention of nephrolithiasis as well. Thus in this paper, we review the complex relationship between salt and nephrolithiasis, pointing out the difference between dietary sodium and salt intake and the best methods to assess them, highlighting the main findings of epidemiologic, laboratory and intervention studies and focusing on open issues such as the role of dietary salt in secondary causes of nephrolithiasis.

Use of the National Health and Nutrition Examination Survey to calculate the impact of obesity and diabetes on cost and prevalence of urolithiasis in 2030

BACKGROUND

The prevalence of urolithiasis and its risk factors such as obesity and diabetes have increased over time.

OBJECTIVE

Determine the future cost and prevalence of kidney stones using current and projected estimates for stones, obesity, diabetes, and population rates.

DESIGN, SETTING, AND PARTICIPANTS

The stone prevalence in 2000 was estimated from the National Health and Nutrition Examination Survey (NHANES) 1988-1994 and 2007-2010. The cost per percentage prevalence of stones in 2000, calculated using Urologic Diseases in America Project data, was used to estimate the annual cost of stones in 2030, adjusting for inflation and increases in population, stone prevalence, obesity and diabetes rates.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The primary outcome was prevalence and cost of stones in 2030. The secondary outcomes were the impact of obesity and diabetes on these values, calculated using odds ratios for stones by body mass index and diabetes status.

RESULTS AND LIMITATIONS

The annual cost of stone disease in 2000, adjusted for inflation to 2014 US dollars, was approximately $2.81 billion. After accounting for increases in population and stone prevalence from 2000, the estimated cost of stones in 2007 in 2014 US dollars was $3.79 billion. Future population growth alone would increase the cost of stone disease by $780 million in 2030. Based on projected estimates for 2030, obesity will independently increase stone prevalence by 0.36%, with an annual cost increase of $157 million. Diabetes will independently increase stone prevalence by 0.72%, associated with a cost increase of $308 million annually by 2030. NHANES data, however, capture patient self-assessment rather than medical diagnosis, which is a potential bias.

CONCLUSIONS

The rising prevalence of obesity and diabetes, together with population growth, is projected to contribute to dramatic increases in the cost of urolithiasis, with an additional $1.24 billion/yr estimated by 2030.

PATIENT SUMMARY

Obesity, diabetes, and population rates will contribute to an estimated $1.24 billion/yr increase in the cost of kidney stones by 2030.

The impact of obesity on the presentation of primary hyperparathyroidism

CONTEXT

Obesity has been associated with elevated serum PTH (sPTH) in the general population. Obesity may also alter the clinical presentation in patients with primary hyperparathyroidism (PHPT).

OBJECTIVES

The objectives of the study were to compare the clinical presentation of obese (OB) vs nonobese (NO) PHPT patients and to assess the impact of obesity on the presentation of PHPT independent of serum calcium and PTH.

PATIENTS

Consecutive PHPT patients who underwent parathyroidectomy between 2003 and 2012 by a single surgical group participated in the study.

SETTING

The study was conducted at an academic medical center.

DESIGN

Cross-sectional review of records of preoperative demographic, historical, laboratory, and densitometry findings and intraoperative pathological findings were compared in OB vs NO patients.

MAIN OUTCOME MEASURES

The prevalence of nephrolithiasis and osteoporosis was measured.

RESULTS

Two hundred forty-seven PHPT patients were included in this analysis. Fifty percent were OB and 79% were women. Mean body mass index was 25.3 ± 3.3 and 36.0 ± 5.2 kg/m(2) in the NO and OB groups, respectively. Age, gender, and race distribution was similar between the two groups. Serum calcium was similar between the groups (11.0 ± 0.7 mg/dL in NO vs 11.1 ± 0.9 mg/dL in OB, P = .13), whereas sPTH was higher in OB (151 ± 70 vs 136 ± 69 pg/mL, P = .03). The OB group exhibited higher prevalence of hypercalciuria (urine calcium > 400 mg per 24 h) (41% vs 23% in NO, P = .01) and nephrolithiasis (36% vs 21% in NO, P = .03). Despite higher sPTH, OB patients showed higher bone mineral density and a lower rate of osteoporosis (21% vs 35%, P = .05). Differences in the prevalence of hypercalciuria and osteoporosis between the groups persisted after adjustment for age, race, estimated glomerular filtration rate, gender, sPTH, and calcium.

CONCLUSIONS

In PHPT patients, obesity is a risk factor for hypercalciuria and nephrolithiasis and is protective against osteoporosis. The impact of parathyroidectomy on the clinical features of obese PHPT patients merits further evaluation.

Prevalence and spot urine risk factors for renal stones in children taking topiramate

INTRODUCTION

Topiramate (TPM), an anti-epileptic drug with >4 million users, increases renal stones in adults. We screened outpatient TPM-treated children without history of stones to estimate the prevalence of renal stones and to characterize urine stone-risk profiles.

METHODS

Children taking TPM ≥1 month underwent an interview, renal ultrasound, and spot urine testing in this prospective study. Normal spot urine values were defined as: calcium/creatinine ratio ≤0.20 mg/mg (>12 months) or ≤0.60 mg/mg (≤12 months), citrate/creatinine ratio >0.50 mg/mg, and pH ≤ 6.7.

RESULTS

Of 41 patients with average age of 9.2 years (range 0.5-18.7), mean TPM dose of 8.0 mg/kg/day (range 1.4-23.6), and mean treatment duration of 27 months (range 1-112), two (4.9%) had renal stones. The majority of children taking TPM had lithogenic abnormalities on spot urine testing, including 21 (51%) with hypercalciuria, 38 (93%) with hypocitraturia, and 28 (68%) with pH ≥ 6.7. Hypercalciuria and hypocitraturia were independent of TPM dose and duration; urine pH increased with dose. 24-h urine parameters improved in 1 stone-former once TPM was weaned.

CONCLUSIONS

Asymptomatic stones were found in 2/41 (4.8%) children taking TPM. Risk factors for stones were present in the spot urine of most children, including hypocitraturia (93%) and hypercalciuria (51%), independent of TPM dose and duration. High urine pH, found in 68%, correlated with TPM dose. Pediatric specialists should be aware of increased risks for stones, hypercalciuria, hypocitraturia, and alkaline urine in children taking TPM.

Hepatitis C co-infection and severity of liver disease as risk factors for osteoporotic fractures among HIV-infected patients

Osteoporosis is increasingly reported in the aging HIV-positive population, and co-infection with hepatitis C virus (HCV) may further increase the risk of osteoporosis. However, it remains unclear whether HCV-related increased fracture risk is a function of the severity of liver disease. We calculated the time-updated alanine aminotransferase to platelet ratio index (APRI) score (an indirect marker of hepatic fibrosis) in all HIV-infected patients enrolled in the Veterans Affairs' Clinical Case Registry between 1984 and 2009. The association between HCV co-infection and incident osteoporotic fracture (defined as closed wrist, vertebral, or hip fracture) was assessed in univariate and multivariate Cox survival models adjusting for traditional risk factors for osteoporosis and APRI score or the presence of cirrhosis. A total of 772 osteoporotic fractures were identified among 56,660 HIV-infected patients (98.1% male; 31.3% HCV co-infected; median age 44.0 years) contributing 305,237 patient-years of follow-up. Fracture rates were significantly higher among HIV/HCV patients than HIV-only patients (2.57 versus 2.07/1000 patient-years, relative risk = 1.24, p < 0.0001). In a Cox multivariable model including age, race, smoking, drug use, body mass index, and antiretroviral therapy, HCV co-infection remained an independent predictor of osteoporotic fractures after controlling for presence of cirrhosis (hazard ratio [HR] = 1.32; p <0.001) or APRI score (HR = 1.30; p = 0.003). Among HIV/HCV co-infected patients, cirrhosis strongly predicted osteoporotic fractures (HR = 1.65; 95% confidence interval [CI] 1.11-2.44; p = 0.012), but APRI score was a weaker predictor (HR = 1.008; 95% CI 1.002-1.014; p = 0.015). In conclusion, among HIV-infected patients, severity of liver disease partly explains the HCV-associated increased risk of osteoporotic fractures. Other determinants of this increased risk remain to be defined.

Body fat content and distribution and urinary risk factors for nephrolithiasis

BACKGROUND AND OBJECTIVES

Obesity is associated with a higher risk of nephrolithiasis. However, it is not known whether higher body fat mass or abnormal fat distribution influences stone risk independent of dietary factors.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In this cross-sectional study, non-stone-forming men with no known kidney disease and with a wide range of body weight collected a 24-hour urine specimen while consuming a fixed metabolic diet. They underwent dual-energy x-ray absorptiometry to assess body composition and fat distribution. Urinary risk factors for nephrolithiasis and urine saturation with respect to calcium oxalate and uric acid (assessed as supersaturation index [SI]) were correlated with various measures of adiposity.

RESULTS

Study participants included 21 men with a mean age of 52.1 years, mean weight of 91.1 kg, and mean total fat mass of 24.3 kg. Twenty-four-hour urine pH and SI uric acid were more closely correlated with fat mass than with lean mass or total body weight. Both 24-hour urine pH and SI uric acid were also significantly correlated with truncal fat mass but not with leg fat mass. Moreover, there was a significant negative correlation between truncal/leg fat mass and NH4(+)/net acid excretion ratio (R=-0.62; P=0.009). However, there was no significant association between SI calcium oxalate and body weight, lean mass, fat mass, trunk fat mass, or leg fat mass.

CONCLUSIONS

The association between 24-hour urine pH and SI uric acid and various measures of adiposity suggest that total body fat and trunk fat are more strongly associated with risk factors for uric acid stone formation than are total body weight and lean body mass. Under a controlled metabolic diet, adiposity is not associated with risk factors for calcium oxalate stones. Further studies are needed to confirm these findings in larger populations that include women and patients who form stones.

Epidemiology of hip fractures in Lebanon: a nationwide survey

INTRODUCTION

Hip fractures are a reliable indicator of osteoporosis. Despite their importance, few studies have assessed their epidemiology in Lebanon and the Middle East.

HYPOTHESES

Hip fracture incidence rates in Lebanon approximate those of Northern countries, and show the same characteristics, particularly the exponential increase with age, higher incidence in women, and a recent trend of rate leveling in women but not in men.

MATERIALS AND METHODS

A national database of hip fracture cases admitted to hospitals in Lebanon in 2007 was created. Crude and age-adjusted incidence rates were calculated at 5-year intervals for individuals over age 50. These rates were also standardized to the 2000 United States population, and compared to those of other countries. Projected incidence rates in Lebanon in 2020 and 2050 were also calculated.

RESULTS

A total of 1199 patients were included in the study. The crude annual incidence rate in individuals over 50 was 147 per 100,000 individuals, 132 per 100,000 males and 160 per 100,000 females, with a female-to-male ratio of 1.2. The age-standardized annual incidence rates (per 100,000) were 180 in males and 256 in females. Assuming unchanged healthcare parameters, the projected crude incidence rates for people over 50 are expected to reach 174 and 284 per 100,000 in 2020 and 2050 respectively.

CONCLUSIONS

Lebanese hip fracture rates are lower than Northern countries, but show many similar characteristics such as an exponential increase with age, a higher incidence in women, and clues of a leveling of rates in women but not in men. Numbers are expected to increase substantially in the coming decades.

LEVEL OF EVIDENCE

Level IV. Epidemiological study.

Effects of sex and postmenopausal estrogen use on serum phosphorus levels: a cross-sectional study of the National Health and Nutrition Examination Survey (NHANES) 2003-2006

BACKGROUND

Elevation of serum phosphorus concentrations has been associated with cardiovascular events in older women and men. Whether age, sex, or estrogen therapy is associated with different phosphorus levels is unknown.

STUDY DESIGN

Cross-sectional study.

SETTING & PARTICIPANTS

7,005 participants in the National Health and Nutrition Examination Survey (NHANES) 2003-2006.

PREDICTORS

Demographic data; body measurement indexes; dietary intake by 24-hour dietary recall and food-frequency questionnaire; data for reproductive health, prescription medication, cardiovascular disease, osteoporosis, and diabetes mellitus obtained by questionnaire; and blood chemistry indexes.

OUTCOMES & MEASUREMENTS

Serum phosphorus concentrations.

RESULTS

In both males and premenopausal females, serum phosphorus levels decline progressively with age. In males, the decline continues over the entire age range of 21-85 years. In contrast, in females, serum phosphorus levels increase between ages 46-60 years (sex×age interaction; P<0.001). The increase in serum phosphorus levels in older women is independent of changes in serum parathyroid hormone levels, daily dietary phosphorus intake, and estimated glomerular filtration rate. In analysis of covariance, we show that postmenopausal women receiving estrogen therapy have significantly lower serum phosphorus levels than non-estrogen users after adjusting for age, race, body mass index, daily dietary phosphorus intake, and serum albumin, serum parathyroid hormone, and 25-hydroxyvitamin D levels (3.83 vs 3.98mg/dL; P<0.001).

LIMITATIONS

The study was cross-sectional in design and estrogen therapy was not randomly assigned or concealed. Important phosphorus regulatory factors such as serum fibroblast growth factor 23 and klotho were not available in the study.

CONCLUSIONS

Estrogen status may account for the difference in serum phosphorus levels in postmenopausal women.

Renal ammonium excretion after an acute acid load: blunted response in uric acid stone formers but not in patients with type 2 diabetes

Idiopathic uric acid nephrolithiasis is characterized by elevated urinary net acid excretion and insufficient buffering by ammonium, resulting in excessively acidic urine and titration of the relatively soluble urate anion to insoluble uric acid. Patients with type 2 diabetes have similar changes in urinary pH, net acid excretion, and ammonium in 24-h urine collections at baseline, even after controlling for dietary factors, and are at increased risk for uric acid nephrolithiasis. However, not all patients with type 2 diabetes develop kidney stones, suggesting that uric acid stone formers may have additional urinary defects, perhaps not apparent at baseline. We performed a metabolic study of 14 patients with idiopathic uric acid nephrolithiasis, 13 patients with type 2 diabetes, and 8 healthy control subjects of similar body mass index. After equilibration on a fixed diet for 5 days, subjects were given a single oral acid load (50 meq ammonium chloride), and urine was collected hourly for 4 h. Uric acid stone formers had a lower ammonium excretory response to acute acid loading compared with diabetic and nondiabetic nonstone formers, suggesting that an ammonium excretory defect unique to uric acid stone formers was unmasked by the acid challenge. The Zucker diabetic fatty rat also did not show impaired urinary ammonium excretion in response to acute acid challenge. A blunted renal ammonium excretory response to dietary acid loads may contribute to the pathogenesis of idiopathic uric acid nephrolithiasis.

Ectopic atypical parathyroid lipoadenoma: a rare cause of severe primary hyperparathyroidism

Parathyroid lipoadenomas are a rare and benign variant of parathyroid adenomas that are defined morphologically by an abundance of fat cells. They may be functional with secretion of parathyroid hormone or nonfunctional. We present a case of a parathyroid lipoadenoma in a patient presenting with clinical manifestations of severe primary hyperparathyroidism. Unusual features in this case included the ectopic location of the lipoadenoma in the mediastinum, the significant size of 6.6 × 3.4 cm, and weight of 30.1 g. In addition to the large size of this generally benign type of parathyroid neoplasm, histologic findings included focal band-forming fibrosis compatible with the diagnosis of an atypical parathyroid adenoma. In conclusion, this case illustrates a difficult case of an ectopic functioning parathyroid lipoadenoma with chronic sequelae due to severe hyperparathyroidism.