Recommendations for High-resolution Peripheral Quantitative Computed Tomography Assessment of Bone Density, Microarchitecture, and Strength in Pediatric Populations

PURPOSE OF REVIEW

The purpose of this review is to summarize current approaches and provide recommendations for imaging bone in pediatric populations using high-resolution peripheral quantitative computed tomography (HR-pQCT).

RECENT FINDINGS

Imaging the growing skeleton is challenging and HR-pQCT protocols are not standardized across centers. Adopting a single-imaging protocol for all studies is unrealistic; thus, we present three established protocols for HR-pQCT imaging in children and adolescents and share advantages and disadvantages of each. Limiting protocol variation will enhance the uniformity of results and increase our ability to compare study results between different research groups. We outline special cases along with tips and tricks for acquiring and processing scans to minimize motion artifacts and account for growing bone. The recommendations in this review are intended to help researchers perform HR-pQCT imaging in pediatric populations and extend our collective knowledge of bone structure, architecture, and strength during the growing years.

Musculoskeletal health in newly diagnosed children with Crohn's disease

We evaluated the impact of Crohn's disease on muscle and bone strength, mass, density, and geometry in children with newly diagnosed CD and found profound muscle and bone deficits; nevertheless, the prevalence of vertebral fractures at this time point was low.

INTRODUCTION

Crohn's disease (CD) is an inflammatory condition of the gastrointestinal tract that can affect the musculoskeletal system. The objective of this study was to determine the prevalence of vertebral fractures and the impact of CD on muscle and bone mass, strength, density, and geometry in children with newly diagnosed CD.

METHODS

Seventy-three children (26 girls) aged 7.0 to 17.7 years were examined within 35 days following CD diagnosis by lateral spine radiograph for vertebral fractures and by jumping mechanography for muscle strength. Bone and muscle mass, density, and geometry were assessed by dual-energy x-ray absorptiometry and peripheral quantitative computed tomography (pQCT).

RESULTS

Disease activity was moderate to severe in 66 (90%) patients. Mean height (Z-score -0.3, standard deviation (SD) 1.1, p = 0.02), weight (Z-score -0.8, SD 1.3, p < 0.01), body mass index (Z-score -1.0, SD 1.3, p < 0.01), lumbar spine areal bone mineral density (BMD; Z-score -1.1, SD 1.0, p < 0.01), total body bone mineral content (Z-score -1.5, SD 1.0, p < 0.01), and total body lean mass (Z-score -2.5, SD 1.1, p < 0.01) were all low for age and gender. pQCT showed reduced trabecular volumetric BMD at the tibial metaphysis, expansion of the bone marrow cavity and thin cortices at the diaphysis, and low calf muscle cross-sectional area. Jumping mechanography demonstrated low muscle power. Only one patient had a vertebral fracture.

CONCLUSIONS

Children with newly diagnosed CD have profound muscle and bone deficits; nevertheless, the prevalence of vertebral fractures at this time point was low.

Assessing community resilience: A CART survey application in an impoverished urban community

This article describes an application of the Communities Advancing Resilience Toolkit (CART) Assessment Survey which has been recognized as an important community tool to assist communities in their resilience-building efforts. Developed to assist communities in assessing their resilience to disasters and other adversities, the CART survey can be used to obtain baseline information about a community, to identify relative community strengths and challenges, and to re-examine a community after a disaster or post intervention. This article, which describes an application of the survey in a community of 5 poverty neighborhoods, illustrates the use of the instrument, explicates aspects of community resilience, and provides possible explanations for the results. The paper also demonstrates how a community agency that serves many of the functions of a broker organization can enhance community resilience. Survey results suggest various dimensions of community resilience (as represented by core CART community resilience items and CART domains) and potential predictors. Correlates included homeownership, engagement with local entities/activities, prior experience with a personal emergency or crisis while living in the neighborhood, and involvement with a community organization that focuses on building safe and caring communities through personal relationships. In addition to influencing residents' perceptions of their community, it is likely that the community organization, which served as a sponsor for this application, contributes directly to community resilience through programs and initiatives that enhance social capital and resource acquisition and mobilization.

Effect of high-dose cholecalciferol (vitamin D3) on bone and body composition in children and young adults with HIV infection: a randomized, double-blind, placebo-controlled trial

It is unknown whether vitamin D supplementation positively impacts body composition and bone outcomes in children and young adults with HIV. This RCT found that despite increasing 25(OH)D concentrations, high dose vitamin D₃ supplementation did not impact bone or body composition in children and young adults with HIV infection.

INTRODUCTION

The objective of this paper was to determine the impact of high-dose daily cholecalciferol (vitamin D₃) supplementation on body composition and bone density, structure, and strength in children and young adults with perinatally acquired (PHIV) or behaviorally acquired (BHIV) HIV infection.

METHODS

Participants were randomized to receive vitamin D₃ supplementation (7000 IU/day) or placebo for 12 months. Serum 25-hydroxyvitamin D [25(OH)D] concentrations, dual energy X-ray absorptiometry (DXA) of the whole body and lumbar spine, and peripheral quantitative computed tomography (pQCT) of tibia sites were acquired at 0, 6, and 12 months. DXA and pQCT outcomes were expressed as sex- and population-ancestry specific Z-scores relative to age and adjusted for height or tibia length, as appropriate.

RESULTS

Fifty-eight participants (5.0 to 24.9 years) received vitamin D₃ supplements (n = 30) or placebo (n = 28). At enrollment, groups were similar in age, sex, population ancestry, growth status, serum 25(OH)D concentrations, body composition, and size-adjusted bone measures. Median 25(OH)D concentrations were similar (17.3 ng/mL in the vitamin D₃ supplementation group vs 15.6 ng/mL in the placebo group), and both groups had mild bone deficits. At 12 months, 25(OH)D rose significantly in the vitamin D supplementation group but not in the placebo group (26.4 vs 14.8 ng/mL, respectively, p < 0.008). After adjusting for population ancestry, sex, antiretroviral therapy use, and season, there were no significant treatment group differences in bone or body composition outcomes.

CONCLUSIONS

Despite increasing 25(OH)D concentrations, 12 months of high-dose vitamin D₃ supplementation did not impact bone or body composition in children and young adults with HIV infection.

Skeletal outcomes by peripheral quantitative computed tomography and dual-energy X-ray absorptiometry in adolescent girls with anorexia nervosa

We conducted the first comparison of dual-energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT) outcomes in adolescent girls with anorexia nervosa. We observed deficits in bone density by both tools. pQCT assessments were associated with many of the same clinical parameters as have been previously established for DXA.

INTRODUCTION

Adolescents with anorexia nervosa (AN) commonly exhibit bone loss, but effects on bone geometry are less clear. We compared measures obtained by DXA and pQCT in girls with AN.

METHODS

Seventy females (age 15.5 ± 1.9 years ) with AN and 132 normal-weighted controls underwent tibial measures by pQCT including trabecular volumetric bone mineral density (vBMD) at the 3 % site, cortical vBMD and dimensions at the 38 % site, and muscle cross-sectional area (CSA) at the 66 % site. Participants with AN also underwent standard DXA measures. Independent t tests compared the pQCT results, while Pearson coefficient assessed correlations among DXA and pQCT measures.

RESULTS

Trabecular vBMD Z-scores were lower in AN compared to controls (AN -0.31 ± 1.42 vs +0.11 ± 1.01, p = 0.01) and cortical vBMD Z-scores were higher (AN +0.18 ± 0.92 vs -0.50 ± 0.88, p < 0.001). Trabecular vBMD and cortical CSA Z-scores positively correlated with DXA BMD Z-scores (r range 0.57-0.82, p < 0.001). Markers of nutritional status positively correlated with Z-scores for trabecular vBMD, cortical CSA, section modulus, and muscle CSA (p < 0.04 for all).

CONCLUSIONS

This study is the first to compare DXA and pQCT measurements in adolescent girls with AN. We observed deficits in BMD by both DXA and pQCT. pQCT assessments correlated well with DXA bone and body composition measures and were associated with many of the same clinical parameters and disease severity markers as have been previously established for DXA. The differences in cortical vBMD merit further study.

Association of 25-hydroxyvitamin D with areal and volumetric measures of bone mineral density and parathyroid hormone: impact of vitamin D-binding protein and its assays

A comparison of the association of different forms of 25-hydroxyvitamin D [25(OH)D] with parathyroid hormone (PTH) and with areal and volumetric bone mineral density (BMD) demonstrated that bioavailable and free 25(OH)D do not provide a better index of vitamin D status in terms of bone health compared to total 25(OH)D.

INTRODUCTION

This study aims to compare measures of vitamin D-binding protein (DBP) using a monoclonal versus polyclonal ELISA and assess correlations of total versus estimated free and bioavailable 25(OH)D with BMD and PTH concentrations.

METHODS

DXA and peripheral quantitative CT (pQCT) scans were obtained in 304 adults (158 black, 146 white), ages 21-80 years. Free and bioavailable 25(OH)D were calculated from total 25(OH)D, DBP, and albumin concentrations. Multivariable linear regression with standardized beta coefficients was used to evaluate associations of bone measures and PTH with total, free, and bioavailable 25(OH)D.

RESULTS

Measures of DBP obtained using a monoclonal versus polyclonal ELISA were not correlated (r s = 0.02, p = 0.76). Free and bioavailable 25(OH)D based on the polyclonal assay were lower in black versus white participants (p < 0.0001); this race difference was not evident using the monoclonal assay. Adjusted for age, sex, calcium intake, and race, all forms of 25(OH)D were negatively associated with PTH, but the absolute coefficient was greatest for total 25(OH)D (-0.34, p < 0.001) versus free/bioavailable 25(OH)D (-0.18/-0.24 depending on DBP assay, p ≤ 0.003). In analyses stratified on race, none of the measures of 25(OH)D were associated with BMD across DXA and pQCT sites.

CONCLUSIONS

The monoclonal versus polyclonal ELISA yielded highly discrepant measures of DBP, particularly among black individuals, likely related to established race differences in DBP polymorphisms. Contrary to prior studies, our findings indicate that using DBP to estimate bioavailable and free 25(OH)D does not provide a better index of vitamin D status in terms of bone health.

Use of proton pump inhibitors is associated with fractures in young adults: a population-based study

Proton pump inhibitors (PPIs) are associated with risk for fracture in osteoporotic adults. In this population-based study, we found a significant association between PPIs and fracture in young adults, with evidence of a dose-response effect. Young adults who use PPIs should be cautioned regarding risk for fracture.

INTRODUCTION

Proton pump inhibitors (PPIs) are associated with fracture in adults with osteoporosis. Because PPI therapy may interfere with bone accrual and attainment of peak bone mineral density, we studied the association between use of PPIs and fracture in children and young adults.

METHODS

We conducted a population-based, case-control study nested within records from general medical practices from 1994 to 2013. Participants were 4-29 years old with ≥ 1 year of follow-up who lacked chronic conditions associated with use of long-term acid suppression. Cases of fracture were defined as the first incident fracture at any site. Using incidence density sampling, cases were matched with up to five controls by age, sex, medical practice, and start of follow-up. PPI exposure was defined as 180 or more cumulative doses of PPIs. Conditional logistic regression was used to estimate the odds ratio and confidence interval for use of PPIs and fracture.

RESULTS

We identified 124,799 cases and 605,643 controls. The adjusted odds ratio for the risk of fracture associated with PPI exposure was 1.13 (95% CI 0.92 to 1.39) among children aged < 18 years old and 1.39 (95% CI 1.26 to 1.53) among young adults aged 18-29 years old. In young adults but not children, we observed a dose-response effect with increased total exposure to PPIs (p for trend <0.001).

CONCLUSIONS

PPI use was associated with fracture in young adults, but overall evidence did not support a PPI-fracture relationship in children. Young adults who use PPIs should be cautioned regarding potentially increased risk for fracture, even if they lack traditional fracture risk factors.

Reduced fracture risk with early corticosteroid withdrawal after kidney transplant

Corticosteroid use after kidney transplantation results in severe bone loss and high fracture risk. Although corticosteroid withdrawal in the early posttransplant period has been associated with bone mass preservation, there are no published data regarding corticosteroid withdrawal and risk of fracture. We hypothesized lower fracture incidence in patients discharged from the hospital without than with corticosteroids after transplantation. From the United States Renal Data System (USRDS), 77, 430 patients were identified who received their first kidney transplant from 2000 to 2006. Fracture incidence leading to hospitalization was determined from 2000 to 2007; discharge immunosuppression was determined from United Networks for Organ Sharing forms. Time-to-event analyses were used to evaluate fracture risk. Median (interquartile range) follow-up was 1448 (808-2061) days. There were 2395 fractures during follow-up; fracture incidence rates were 0.008 and 0.0058 per patient-year for recipients discharged with and without corticosteroid, respectively. Corticosteroid withdrawal was associated with a 31% fracture risk reduction (HR 0.69; 95% CI 0.59-0.81). Fractures associated with hospitalization are significantly lower with regimens that withdraw corticosteroid. As this study likely underestimates overall fracture incidence, prospective studies are needed to determine differences in overall fracture risk in patients managed with and without corticosteroids after kidney transplantation.

False positive carbohydrate antigen 19-9 (CA19-9) results due to a low-molecular weight interference in an apparently healthy male

BACKGROUND

We investigated the presence of interference in a patient who had an elevated CA19-9 concentration using the ADVIA Centaur but results within reference limits with ROCHE Modular Analytics E170 and Brahms KRYPTOR analysers.

METHODS

We performed repeat analyses using the same (ADVIA Centaur) and alternate immunossays (Roche Modular Analytics E170 and Brahms KRYPTOR) on the patient's sample and investigated for known interferences. To determine the nature of the interference, we measured CA19-9 on the ADVIA Centaur after dilution experiments and after incubation with non-immune animal sera and in heterophilic blocking tubes (HBT). We also undertook polyethylene glycol precipitation, lectin inhibition experiments and gel filtration chromatography.

RESULTS

A curvilinear response to dilution was observed with the ADVIA Centaur. Other known interferences were excluded. Treatment with HBT or non-immune animal sera did not give clinically different results from untreated samples. There was only 0.59% recovery after PEG precipitation in the sample from the case patient. Lectin reduced the assay signal in four patient samples (recovery=1.9-14.1%) but not in the case patient (recovery=106.2%). Gel filtration studies suggested the presence of a low molecular weight (approximately 100 kDa) interference in the case patient's serum.

CONCLUSIONS

We report a novel mode of interference and show a non-CA19-9, low molecular-weight interference affecting the ADVIA Centaur CA19-9 immunoassay.

Serum alkaline phosphatase reflects post-Fontan hemodynamics in children

Although survivors of Fontan palliation for a single ventricle are known to have lower cardiac index than patients with two-ventricle surgical reconstructions, it is unclear whether two frequently observed sequelae, short stature and protein-losing enteropathy (PLE), have hemodynamic origins. A serum marker that reflects hemodynamic status would be a tremendous asset in the long-term management of children with these sequelae. The authors recently noted severely reduced total alkaline phosphatase (TALP) levels in two children with early-onset PLE after Fontan operations, both of whom had low cardiac output at cardiac catheterization. Catheter-based or surgical interventions that rapidly increased cardiac output in these two patients resulted not only in relief of PLE but also in a prompt TALP rise. To examine whether the apparent correlation of low TALP with impaired cardiac output also is seen in Fontan patients without PLE, this study retrospectively examined the TALP data from two other Fontan patients who underwent cardiac catheterization specifically to assess the potential benefit of vasodilator therapy. The TALP levels were abnormally low in both cases but increased after up-titration of angiotensin-converting enzyme inhibition. Serum TALP activity, an indicator of osteoblastic function particularly in pre-adolescence, may be a marker of low cardiac output after a Fontan operation.

Special report on the 2007 adult and pediatric Position Development Conferences of the International Society for Clinical Densitometry

The International Society for Clinical Densitometry (ISCD) conducts Position Development Conferences (PDCs) for the purpose of establishing standards and guidelines in the field of bone densitometry. Topics for consideration are selected according to clinical relevance, a perceived need for standardization, and the likelihood of achieving agreement. Questions regarding nomenclature, indications, acquisition, analysis, quality control, interpretation, and reporting of bone density tests for each topic area are assigned to task forces for a comprehensive review of the scientific literature. The findings of the review and recommendations are then presented to an international panel of experts at the PDC. The expert panel votes on potential Official Positions for appropriateness, necessity, quality of the evidence, strength of the recommendation, and applicability (worldwide or variable according to local requirements). Recommendations that are approved by the ISCD Board of Directors become Official Positions. The first Pediatric PDC was 20-21 June 2007 in Montreal, QC, Canada. The most recent Adult PDC was held 20-22 July 2007, in Lansdowne, VA, USA. This Special Report summarizes the methodology of the ISCD PDCs and presents selected Official Positions of general interest.

Childhood onset arthritis is associated with an increased risk of fracture: a population based study using the General Practice Research Database

BACKGROUND

Childhood onset arthritis is associated with low bone mass and strength.

OBJECTIVE

To determine whether childhood onset arthritis is associated with greater fracture risk.

METHODS

In a retrospective cohort study all subjects with onset of arthritis between 1 and 19 years of age in the United Kingdom General Practice Research Database were identified. As controls, all sex and age matched subjects from a practice that included a subject with arthritis were included. Incidence rate ratios (IRRs) for first fracture were generated using Mantel-Haenszel methods and Poisson regression.

RESULTS

1939 subjects with arthritis (51% female) and 207 072 controls (53% female) were identified. The median age at arthritis diagnosis was 10.9 years. A total of 129 (6.7%) first fractures were noted in subjects with arthritis compared with 6910 (3.3%) in controls over a median follow up of 3.90 and 3.95 years in the subjects with arthritis and controls, respectively. The IRR (95% confidence interval) for first fracture among subjects with arthritis, compared with controls, according to the age at the start of follow up were 1.49 (0.91 to 2.31) for age <10 years, 3.13 (2.21 to 4.33) at 10-15 years, 1.75 (1.18 to 2.51) at 15-20 years, 1.40 (0.91 to 2.08) at 20-45 years, and 3.97 (2.23 to 6.59) at >45 years.

CONCLUSIONS

Childhood onset arthritis is associated with a clinically significant increased risk of fracture in children, adolescents and, possibly, adults. Studies are urgently needed to characterise the determinants of structural bone abnormalities in childhood arthritis and devise prevention and treatment strategies.

Adverse neurologic events associated with rebound hypertension after using short-acting nifedipine in childhood hypertension

INTRODUCTION

Short-acting nifedipine (SA-NIF) is widely prescribed for acute hypertension (HTN) in children despite reports of ischemic complications in adults. We describe two children with neurologic events caused by rebound hypertension following SA-NIF use.

CASES

Patient 1 is a 7-year-old with acute nephritis and blood pressure (BP) of 185/130. She received SA-NIF which decreased BP to 114/79. When BP rebounded to 160/103, she developed severe cortical visual impairment. Head CT demonstrated edema and petechial hemorrhages in the watershed region. Patient 2 is a 10-year-old renal transplant recipient who received SA-NIF for a BP of 155/98, which resulted in a prompt decrease to 114/74. Two hours later he developed aphasia and right-sided neglect. His BP increased to 168/88 and he developed partial complex seizures. Brain MRI showed high signal intensity in the watershed areas with early gadolinium enhancement.

DISCUSSION

The temporal association of the neurologic events with the rebound increase in BP suggests a possible role for the SA-NIF, consistent with its pharmacokinetic profile. Although the adult literature has focused on the unpredictable decline in BP after SA-NIF treatment, these cases suggest that rapid increases in BP following the maximal SA-NIF effect may be associated with impaired cerebral autoregulation and encephalopathy in children. These cases underscore the need for frequent blood pressure determinations and therapy to prevent rebound hypertension.

Assessment of bone mineralization following renal transplantation in children: limitations of DXA and the confounding effects of delayed growth and development

Pediatric renal transplantation recipients have numerous risk factors for decreased bone mass, including the underlying renal disease, nutritional deficits, decreased physical activity, inflammation and exposure to steroid therapy. The assessment of bone mineralization in children following renal transplantation is fraught with difficulty. Dual energy x-ray absorptiometry (DXA) is the most commonly employed tool to assess bone mineralization. However, DXA has important limitations in children and in individuals with renal disease. This brief review will examine the expected gains in bone size and bone mass during growth and the mechanisms by which renal failure and steroid therapy interrupt these process. In addition, the limitations of DXA for detecting impaired bone mineralization in children with renal disease are reviewed and alternative approaches explored.

Variability among pediatric nephrologists in the initial therapy of nephrotic syndrome

The objective of this study was to describe the practices of North American pediatric nephrologists in treating new-onset steroid-sensitive nephrotic syndrome and impressions regarding the effect of therapy duration on the risk of relapse. A questionnaire was mailed to 130 pediatric nephrologists in the United States and Canada. One hundred and five (81%) replied. Of the respondents, 39% believed a longer steroid regimen results in more-sustained remissions; 19% did not; 18% believed perhaps, but not enough to risk the increased side-effects of the longer steroid regimen; and 24% did not know. Half of the respondents prescribed an 8-week regimen and 21% prescribed a 12-week regimen; however, in 70% of both regimens, respondents appended an additional taper. The remaining respondents either tapered at urinary remission (14%) or used another regimen (15%). Physicians using the 12-week regimen expected 44% of patients to be relapse free at 1 year, compared with 31% of patients of respondents using other regimens (P=0.005). Over the previous 5 years, 38% of respondents changed their approach; of these, 70% lengthened the treatment course. Physician perceptions and strategies did not vary according to years of clinical experience. In conclusion, there is significant variability in practice and perceptions among pediatric nephrologists; however, most have extended therapy beyond the traditional 8-week course.

Increased urinary transforming growth factor-beta(1) excretion in children with posterior urethral valves

OBJECTIVES

Patients with posterior urethral valves (PUV) are at significant risk for progression to end-stage renal disease, despite early correction of the obstruction. Experimental models of urinary obstruction demonstrate increased renal expression of the profibrotic inflammatory mediator, transforming growth factor-beta(1) (TGF-beta(1)). Urinary TGF-beta(1) excretion is elevated in certain glomerular diseases, but has not been well studied in patients with obstructive lesions. The objective of this study was to examine urinary TGF-beta(1) excretion in children with PUV.

METHODS

Fourteen patients with PUV, aged 3.2 to 14.5 years, with estimated glomerular filtration rates (GFRs) of 12.8 to 139 mL/min/1.73 m(2) were enrolled. Sixteen normal subjects (9 male, 7 female), aged 4.3 to 20.5 years, served as controls. Total urinary TGF-beta(1) concentration was assayed by enzyme-linked immunoabsorbent assay, and expressed as a ratio to urinary creatinine concentration.

RESULTS

Urinary TGF-beta(1) excretion was significantly greater in patients with PUV (range 0 to 0.063, median 0.019 ng/mg urine creatinine) compared with that of healthy controls (range 0 to 0.022, median 0.005 ng/mg urine creatinine) (P <0.01). There was no correlation between urinary TGF-beta(1) excretion and estimated GFR, past urinary diversion surgery, or bladder wall thickening. Among healthy controls, urinary TGF-beta(1) was not correlated with age or gender.

CONCLUSIONS

Results from this study suggest that TGF-beta(1) may contribute to progressive renal insufficiency in patients with PUV. Further studies are indicated to determine if agents that affect TGF-beta(1) expression, such as angiotensin-converting enzyme inhibitors, can slow the progression of renal disease in PUV.

Early risk factors for increased adiposity: a cohort study of African American subjects followed from birth to young adulthood

BACKGROUND

Obesity is an increasing concern in the United States. Effective prevention of obesity requires the risk factors to be well defined. African Americans have a high risk of obesity.

OBJECTIVE

The objective of this study was to identify risk factors, present at birth, for increased adiposity in adulthood in an African American population.

DESIGN

In this retrospective analysis of a prospective cohort study, anthropometric and socioeconomic variables were collected at birth. A representative sample of 447 African American subjects was followed up until young adulthood, when skinfold thickness was measured. Associations between the independent variables and increased adiposity (skinfold thickness above the 85th percentile) were explored by using unadjusted and adjusted analyses.

RESULTS

Three variables measured at birth were independently associated with adiposity in young adulthood, explaining 12% of the variance. The odds ratios (with 95% CIs) of these variables for increased adiposity were 2.7 (1.2, 6.2) for female sex, 4.0 (1.4, 11. 2) for first-born status, and 1.15 (1.06, 1.25) for each unit increment in maternal prepregnancy body mass index (BMI; in kg/m(2)). After adjustment for these variables, birth weight for gestational age and socioeconomic variables were not associated with adiposity.

CONCLUSIONS

This cohort study of African American subjects was the first to identify first-born status as an independent risk factor for increased adiposity in adulthood in a US population. The results of the study strengthen previous reports of the effect of female sex and maternal BMI on adulthood obesity. Identification of risk factors early in life may help target prevention toward high-risk children and allow healthy lifestyles to be established before the onset of obesity.

Autosomal dominant hemolytic uremic syndrome: variable phenotypes and transplant results

Autosomal dominant hemolytic uremic syndrome (ADHUS) is a rare disorder with a poor prognosis that was considered to present mainly in adults. Recurrent episodes of ADHUS were also thought to be uncommon. However, increasing reports suggest that children are often affected, that recurrent episodes may occur pretransplantation, and that post-transplant recurrences occur in about 50% of cases. We describe the occurrence of ADHUS in two unrelated families with different outcomes. It is apparent that there are several types of ADHUS (with and without serum complement abnormalities) and that there may be variable expression of the phenotype. There was variable penetration of HUS in four (possibly five) adults and two children in four generations of one kindred. There was also one definite unaffected carrier. Two patients had successful renal transplants without recurrences; the HUS recurred in a third patient soon after transplantation. In a second family, the father had three episodes of HUS at 18, 26 and 29 years of age; his son had one episode of HUS at 5 years of age. Both recovered completely. Evaluation of these patients, previous reports, and follow-up contacts of previous reports suggests that post-transplant recurrence of ADHUS is more common than previously reported and may not be prevented by prior nephrectomy of native kidneys.

Discrepancies in pediatric bone mineral density reference data: potential for misdiagnosis of osteopenia

OBJECTIVE

To evaluate published pediatric dual-energy x-ray absorptiometry bone mineral density (BMD) reference data by comparing the diagnostic classification of measured BMD in children at risk for osteopenia as healthy or osteopenic according to reference source.

STUDY DESIGN

Spine BMD was measured in 95 children, ages 9 to 15 years, at risk for osteopenia because of childhood disease. The BMD results were converted to age-specific z scores for each of the 5 reference data sets, and the z -score distributions were compared.

RESULTS

Between 11% and 30% of children were classified as osteopenic (z score < -2.0) depending on the reference data set. The 2 sex-specific reference data sets yielded similar diagnostic classification of boys and girls: 10% of boys and 11% to 16% of girls were osteopenic (P =.4). The 3 sex-nonspecific reference data sets classified 9% to 13% of girls and 24% to 44% of boys as osteopenic; the diagnosis of osteopenia was significantly greater in boys (P <.01).

CONCLUSIONS

The use of different published reference data for the assessment of children at risk for osteopenia results in inconsistent diagnostic classification of BMD results. These inconsistencies can be partially attributed to sex-nonspecific reference data that result in misclassification of boys as osteopenic.

Evaluation of low density spine software for the assessment of bone mineral density in children

Pediatric dual-energy X-ray absorptiometry spine scans often cannot be analyzed with standard software due to a failure to identify the bone edges of low density vertebrae. Low density spine (LDS) software improves bone detection compared with standard software. The objective of this study was to compare bone mineral density (BMD) measurements obtained with the standard and LDS software in 27 healthy nonobese, 32 obese, and 41 chronically ill children, ages 2-18 years. Lumbar spine (L1-L4) BMD, measured by standard analysis, ranged from 0.531-1.244 gm/cm2. Reanalysis with the LDS software resulted in a systematic increase (mean +/- SD) in estimated bone area of 17.0+/-5.0%, an increase in bone mineral content of 6.1+/-6.3%, and a mean decrease in BMD of 8.7+/-1.7% (all p < 0.001). This resulted in a mean decrease in BMD Z score of 0.7+/-0.2. Linear regression models, predicting standard BMD from LDS BMD, were fit for the three subject groups (R2 = 0.993-0.995). Small differences in slopes were detected across groups (p = 0.07); LDS BMD predicted higher standard BMD in obese subjects. In conclusion, LDS analysis resulted in a clinically significant decrease in measured BMD. The association between analysis methods was exceptionally high (R2 > 0.99), indicating that LDS BMD accurately predicts standard BMD. Although LDS BMD in obese subjects predicts higher standard BMD results than in nonobese subjects, the small difference is of questionable clinical significance. LDS software is a useful tool for the assessment of BMD in children.

Incorrect diagnosis of diabetes mellitus in a patient with persistence of fetal haemoglobin

A 65-year-old woman, referred to the endocrine clinic for investigation of tiredness and arthritis, was diagnosed as having diabetes on the basis of a positive family history and a raised glycated haemoglobin (HbA1) measurement. Subsequently, she was shown not to have diabetes but to have a persistently raised haemoglobin F (HbF) level. Initial assessment of HbF level by electroendosmosis demonstrated a normal HbF level but high values were confirmed using HPLC. Thalassaemia was excluded following DNA analysis. This case illustrates the importance of a glucose tolerance test following WHO criteria for the diagnosis of diabetes and emphasises that HbA1 is not a diagnostic test for diabetes.

Interaction between tacrolimus and chloramphenicol in a renal transplant recipient

BACKGROUND

The metabolism of tacrolimus is influenced by several medications when they are given concurrently. We report the interaction between tacrolimus and chloramphenicol in a renal transplant recipient.

METHODS

An adolescent with vancomycin-resistant Enterococcus was given standard doses of chloramphenicol. Tacrolimus trough levels increased, and the dose was adjusted to maintain the target trough level. Pharmacokinetic studies were obtained during chloramphenicol administration and 14 days after its discontinuation.

RESULTS

Toxic levels of tacrolimus were seen on the second day of chloramphenicol administration, requiring an 83% reduction in the tacrolimus dose. The dose-adjusted area under the curve value for tacrolimus was 7.5-fold greater while the patient was on chloramphenicol. These data are consistent with inhibition of tacrolimus clearance by chloramphenicol

CONCLUSIONS

Chloramphenicol interferes with tacrolimus metabolism. Careful monitoring of tacrolimus trough levels during concomitant chloramphenicol therapy is recommended to avoid toxicity.

Plasma zinc status, growth, and maturation in children with sickle cell disease

OBJECTIVE

The objective of this study was to determine the relation of plasma zinc (Zn) status to growth and maturation in children with SS genotype sickle cell disease.

STUDY DESIGN

A cross-sectional study of 104 subjects who were 50% female and ranged in age from 0.4 to 18 years was performed. Measures included plasma Zn concentration (Znp), height, weight, skinfold thicknesses, elbow breadth, upper arm muscle area, and fat-free mass and fat mass by total body electrical conductivity. Skeletal maturation was assessed by hand-wrist x-ray evaluation and sexual maturation by Tanner stage.

RESULTS

A total of 44% of the patients had low Znp (<10.7 micromol/L [70 microg/dl]); those with low Znp had significantly lower SD scores for height (p = 0.003), weight (p = 0.003), upper arm muscle area (p = 0.045), fat-free mass (p = 0.025), and elbow breadth (p = 0.017) and greater skeletal maturation delay (p = 0.04). In older children (>9 years) low Znp was associated with decreased Tanner scores for pubic hair (p = 0.001) and breast and genital maturation (p = 0.009). No significant differences were seen in age, sex, or fat stores according to Zn status.

CONCLUSIONS

Decreased plasma Zn is common in children with SS genotype sickle cell disease and is associated with decreased linear growth, skeletal growth, muscle mass, and sexual and skeletal maturation.

Effects of the enantiomers of R,S-salbutamol on incompletely fused tetanic contractions of slow- and fast-twitch skeletal muscles of the guinea-pig

1. The effects of racemic R,S-salbutamol, and its individual enantiomers have been studied on incompletely fused (sub-tetanic) contractile responses of fast- and slow-contracting isolated skeletal muscles of the guinea-pig. 2. R,S-salbutamol (2-4 microM) decreased the peak force of sub-tetani in the slow-contracting soleus muscle and increased the peak force of sub-tetani in the fast-contracting peroneus longus muscle. It also increased the force of the first twitch of sub-tetani in both muscles. The decrease in the peak force of sub-tetani in the soleus muscle was due to defusion of the individual twitches caused by a shortening of their time course. 3. The effects of 4 microM of the racemate on both fast- and slow-contracting muscles were mimicked by 2 microM R-salbutamol (levalbuterol). However, 2 microM S-salbutamol was devoid of activity in both muscles. 4. We concluded that all the effects of R,S-salbutamol on guinea-pig skeletal muscles are due to the activity of the R-enantiomer. Thus there is a common enantiomeric profile for the skeletal muscle and bronchorelaxant activity of the compound.

Helicobacter pylori does not release cysteamine into gastric juice

AIM

To determine whether Helicobacter pylori releases cysteamine into gastric juice as cysteamine is known to be ulcerogenic.

METHODS

Samples of fasting gastric juice were collected from 22 individuals (four women); 10 subjects were H pylori negative. The presence of infection was confirmed by examination and culture of gastric biopsies. Cysteamine in gastric juice was measured by reversed phase gradient high performance liquid chromatography with a detection limit of 10 mumol/l.

RESULTS

Cysteamine was not detected in any of the gastric juice samples or in extracts of cultured H pylori.

CONCLUSIONS

If H pylori produces cysteamine then the amounts produced are insignificant and are unlikely to explain the association between H pylori infection and the development of duodenal ulcer disease.

An incidental finding of Gitelman's syndrome

Gitelman's syndrome is characterised by hypokalaemia, hypomagnesaemia and tetany. This rare disorder is not well described in the literature, probably due to its similarity with Bartter's syndrome. We describe the symptoms and treatment of a young patient whom we consider to have Gitelman's syndrome.

A quality assessment scheme for blood glucose monitoring: competition improves performance

Quality assurance procedures are often ignored or forgotten about by wards involved in the blood glucose monitoring of patients. We have devised a complete quality assurance scheme for checking the ward performance of 38 B-M Reflolux meters and two B-M Accutrend meters. Quality control (QC) material, supplied commercially and distributed by the laboratory, is analysed and recorded daily by the wards (internal QC). In addition, a 'spiked', whole blood sample is prepared by the laboratory and distributed for analysis to all wards at six-monthly intervals (external QC). The laboratory also conducts a monthly survey of meter operation (quality assessment) based on a 'scoring system' that allows easy identification of poor performers. Poor performers are counselled accordingly and, if poor performance is persistent, their meter is removed. In our experience, the publication and distribution of ward quality assessment scores has increased competition between wards in terms of avoiding low scores, dramatically improved performance, and ultimately led to improved patient care.

Free radical activity in young adult cigarette smokers

Cigarette smoke is capable of generating free radicals. In this study markers of free radical activity (thiobarbituric acid reactivity, superoxide dismutase and glutathione peroxidase) were measured in young adult smoking and non-smoking volunteers. No significant differences were found in any of the free radical markers between the two groups. The number of leucocytes was elevated and a positive correlation was found between the number of leucocytes and thiobarbituric acid reactivity in the smokers. The results from this study suggest that any free radical activity generated from long term cigarette smoking in young adults is adequately scavenged.

Cigarette smoking and free radical activity in young adults with insulin-dependent diabetes

Cigarette smoke is potentially capable of generating a high free radical load in the body and many patients with diabetes are smokers. This study was designed to investigate the relationship between long-term smoking and free radical activity in young adult insulin-dependent diabetic patients with no evidence of macrovascular disease. Eight-five patients (48 male) aged 17-40 years were studied. Mean duration of diabetes was 10.5 years (0.08-33) and 39 were cigarette smokers. All had normal serum creatinine levels. The free radical markers measured were: thiobarbituric acid reactive substances, glutathione peroxidase, and superoxide dismutase. No significant differences in thiobarbituric acid reactive substances, glutathione peroxidase, or superoxide dismutase, were found between the diabetic smokers and non-smokers. Also no difference was found comparing the diabetic patients with 40 non-diabetic control subjects (20 smokers). Persistent albuminuria was present in 16 patients (10 microalbuminuria) and free radical marker concentrations in these subjects were similar to the normoalbuminuric patients. This data suggests that any increase in free radical activity due to cigarette smoke is adequately scavenged in young adults with diabetes who are free of significant macrovascular disease.

Continuous parenteral infusion of vitamin E pharmacokinetics and bilirubin production in premature neonates

We conclude that 5 mg/kg of vitamin E, administered intra-arterially as an 8-hour continuous infusion, significantly and predictably raises serum vitamin E levels into the supraphysiologic range with no apparent side effects. In a group of premature infants whose initial serum vitamin E levels were generally greater than or equal to 0.5 mg/dL, no decrease in bilirubin production was observed. Thus, vitamin E deficiency probably does not play a prominent role in jaundice of prematurity.

Vancomycin pharmacokinetics in very low birth weight neonates

The pharmacokinetics of vancomycin hydrochloride was studied in 12 very low birth weight infants. The gestational age (mean +/- SD) was 25.9 +/- 1.3 weeks and body weight was 769.2 +/- 151.5 g at the time of initiation of the study. Vancomycin was infused over a period of 60 minutes in a dosage of 14.2 +/- 3.2 mg/kg once daily in 10 patients, twice daily in 1 patient and every 36 hours in 1 patient for a mean of 10.5 +/- 4.9 days. Serial blood samples were obtained and the concentration time data were fitted to a one-compartment open model using the ADAPT computer program. A significant positive correlation was found between postconceptional age and vancomycin clearance (P less than 0.005) and between vancomycin elimination half-life and plasma creatinine (P less than 0.01). A negative correlation existed between plasma creatinine and vancomycin clearance (P less than 0.005), between postconceptional age and plasma creatinine (P less than 0.005) and between vancomycin half-life and postconceptional age (P less than 0.01). On the basis of these findings a vancomycin dosage of 15 mg/kg every 24 hours for infants less than 1000 g should yield concentrations within the accepted therapeutic range. This susceptible population requires frequent monitoring of vancomycin concentrations because of the high degree of interpatient variability and the continuous maturation of renal function.

Interpreting the carboxyhaemoglobin concentration in fetal cord blood

We calculated the fetal-to-maternal carboxyhaemoglobin concentration ratio in 19 mother-infant pairs at the time of term delivery. Mothers, who had a less than 10% drop in their carboxyhaemoglobin concentration during labour, had an average ratio of 1.40 +/- 0.19. For mothers whose carboxyhaemoglobin concentrations dropped by 10% or more during labour, the average fetal-to-maternal carboxyhaemoglobin concentration ratio was 1.83 +/- 0.48. There was a strong correlation (r = 0.82) between the percent change in maternal carboxyhaemoglobin concentration during labour and the fetal-to-maternal carboxyhaemoglobin concentration ratio at the time of delivery. We conclude that increased CO elimination during labour may be accompanied by rapid changes in the maternal carboxyhaemoglobin concentration, leading to a spuriously high fetal-to-maternal carboxyhemoglobin concentration ratio at the time of delivery.

Psoas abscess: changing patterns of diagnosis and etiology

From 1976 to 1984, 43 patients with psoas abscess were seen at the Mayo Clinic. Intestinal disease, including Crohn's disease, diverticulitis, and carcinoma, was the most frequent cause (14 patients). Eleven patients had osteomyelitis, five had postoperative complications, four had a foreign-body reaction, and three had a primary staphylococcal abscess. Two patients each had extension of a primary pancreatic and perinephric abscess. One patient had tuberculosis of the spine, and in the remaining patient, an exact cause was not determined. Definitive treatment of psoas abscess includes adequate debridement, drainage of the abscess cavity, and resection of involved bowel.

The effects of sorbinil on peripheral nerve conduction velocity, polyol concentrations and morphology in the streptozotocin-diabetic rat

This study examined the effects of an aldose reductase inhibitor, Sorbinil, on neuropathy over a 6-month period in streptozotocin-diabetic rats. Sorbinil treatment prevented the 10-fold increase in nerve sorbitol found with diabetes. It produced a 60% improvement in tibial nerve motor conduction velocity after 6 months. Morphometric profiles of nerves were also normalized. Axon area was reduced by 14% in untreated diabetic rats compared to age-matched controls, whereas Sorbinil-treated animals showed normal age-related axon growth. Myelin area was increased by 28% in untreated diabetic animals, but was the same as age-matched controls with Sorbinil treatment. Nerve myo-inositol levels were reduced by 45% after three months of untreated diabetes, but were normal after six months. Sorbinil treatment tended to restore myo-inositol levels toward normal over the shorter time period. It was concluded that axon growth retardation is the most likely cause of the conduction deficit seen in long-term experimental diabetes.