Hungry bone syndrome and normalisation of renal phosphorus threshold after total parathyroidectomy for tertiary hyperparathyroidism in X-linked hypophosphataemia: a case report

Forestalling Hungry Bone Syndrome after Parathyroidectomy in Patients with Primary and Renal Hyperparathyroidism

Hungry bone syndrome (HBS), severe hypocalcemia following parathyroidectomy (PTX) due to rapid drop of PTH (parathormone) after a previous long term elevated concentration in primary (PHPT) or renal hyperparathyroidism (RHPT), impairs the outcome of underlying parathyroid disease.

OBJECTIVE

overview HBS following PTx according to a dual perspective: pre- and post-operative outcome in PHPT and RHPT. This is a case- and study-based narrative review.

INCLUSION CRITERIA

key research words "hungry bone syndrome" and "parathyroidectomy"; PubMed access; in extenso articles; publication timeline from Inception to April 2023.

EXCLUSION CRITERIA

non-PTx-related HBS; hypoparathyroidism following PTx. We identified 120 original studies covering different levels of statistical evidence. We are not aware of a larger analysis on published cases concerning HBS (N = 14,349). PHPT: 14 studies (N = 1545 patients, maximum 425 participants per study), and 36 case reports (N = 37), a total of 1582 adults, aged between 20 and 72. Pediatric PHPT: 3 studies (N = 232, maximum of 182 participants per study), and 15 case reports (N = 19), a total of 251 patients, aged between 6 and 18. RHPT: 27 studies (N = 12,468 individuals, the largest cohort of 7171) and 25 case reports/series (N = 48), a total of 12,516 persons, aged between 23 and 74. HBS involves an early post-operatory (emergency) phase (EP) followed by a recovery phase (RP). EP is due to severe hypocalcemia with various clinical elements (<8.4 mg/dL) with non-low PTH (to be differentiated from hypoparathyroidism), starting with day 3 (1 to 7) with a 3-day duration (up to 30) requiring prompt intravenous calcium (Ca) intervention and vitamin D (VD) (mostly calcitriol) replacement. Hypophosphatemia and hypomagnesiemia may be found. RP: mildly/asymptomatic hypocalcemia controlled under oral Ca+VD for maximum 12 months (protracted HBS is up to 42 months). RHPT associates a higher risk of developing HBS as compared to PHPT. HBS prevalence varied from 15% to 25% up to 75-92% in RHPT, while in PHPT, mostly one out of five adults, respectively, one out of three children and teenagers might be affected (if any, depending on study). In PHPT, there were four clusters of HBS indicators. The first (mostly important) is represented by pre-operatory biochemistry and hormonal panel, especially, increased PTH and alkaline phosphatase (additional indicators were elevated blood urea nitrogen, and a high serum calcium). The second category is the clinical presentation: an older age for adults (yet, not all authors agree); particular skeleton involvement (level of case reports) such as brown tumors and osteitis fibrosa cystica; insufficient evidence for the patients with osteoporosis or those admitted for a parathyroid crisis. The third category involves parathyroid tumor features (increased weight and diameter; giant, atypical, carcinomas, some ectopic adenomas). The fourth category relates to the intra-operatory and early post-surgery management, meaning an associated thyroid surgery and, maybe, a prolonged PTx time (but this is still an open issue) increases the risk, as opposite to prompt recognition of HBS based on calcium (and PTH) assays and rapid intervention (specific interventional protocols are rather used in RHPT than in PHPT). Two important aspects are not clarified yet: the use of pre-operatory bisphosphonates and the role of 25-hydroxyitamin D assay as pointer of HBS. In RHPT, we mentioned three types of evidence. Firstly, risk factors for HBS with a solid level of statistical evidence: younger age at PTx, pre-operatory elevated bone alkaline phosphatase, and PTH, respectively, normal/low serum calcium. The second group includes active interventional (hospital-based) protocols that either reduce the rate or improve the severity of HBS, in addition to an adequate use of dialysis following PTx. The third category involves data with inconsistent evidence that might be the objective of future studies to a better understanding; for instance, longer pre-surgery dialysis duration, obesity, an elevated pre-operatory calcitonin, prior use of cinalcet, the co-presence of brown tumors, and osteitis fibrosa cystica as seen in PHPT. HBS remains a rare complication following PTx, yet extremely severe and with a certain level of predictability; thus, the importance of being adequately identified and managed. The pre-operatory spectrum of assessments is based on biochemistry and hormonal panel in addition to a specific (mostly severe) clinical presentation while the parathyroid tumor itself might provide useful insights as potential risk factors. Particularly in RHPT, prompt interventional protocols of electrolytes surveillance and replacement, despite not being yet a matter of a unified, HBS-specific guideline, prevent symptomatic hypocalcemia, reduce the hospitalization stay, and the re-admission rates.

PTH and FGF23 Exert Interdependent Effects on Renal Phosphate Handling: Evidence From Patients With Hypoparathyroidism and Hyperphosphatemic Familial Tumoral Calcinosis Treated With Synthetic Human PTH 1-34

Parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23) both influence blood phosphate levels by regulating urinary phosphate reabsorption. Clinical data suggest that adequate renal phosphate handling requires the presence of both FGF23 and PTH, but robust evidence is lacking. To investigate whether the phosphaturic effects of PTH and FGF23 are interdependent, 11 patients with hypoparathyroidism, which features high blood phosphate in spite of concomitant FGF23 elevation, and 1 patient with hyperphosphatemic familial tumoral calcinosis (HFTC), characterized by deficient intact FGF23 action and resulting hyperphosphatemia, were treated with synthetic human PTH 1-34 (hPTH 1-34). Biochemical parameters, including blood phosphate, calcium, intact FGF23 (iFGF23), nephrogenic cAMP, 1,25(OH)₂ vitamin D (1,25D), and tubular reabsorption of phosphate (TRP), were measured at baseline and after hPTH 1-34 treatment. In patients with hypoparathyroidism, administration of hPTH 1-34 increased nephrogenic cAMP, which resulted in serum phosphate normalization followed by a significant decrease in iFGF23. TRP initially decreased and returned to baseline. In the patient with HFTC, hPTH 1-34 administration also increased nephrogenic cAMP, but this did not produce changes in phosphate or TRP. No changes in calcium were observed in any of the studied patients, although prolonged hPTH 1-34 treatment did induce supraphysiologic 1,25D levels in the patient with HFTC. Our results indicate that PTH and FGF23 effects on phosphate regulation are interdependent and both are required to adequately regulate renal phosphate handling. Published 2021. This article is a U.S. Government work and is in the public domain in the USA.

Combined treatment by burosumab and a calcimimetic can ameliorate hypophosphatemia due to excessive actions of FGF23 and PTH in adult XLH with tertiary hyperparathyroidism: A case report

INTRODUCTION

X-linked hypophosphatemia (XLH) is the most prevalent type of heritable fibroblast growth factor 23 (FGF23)-related hypophosphatemic rickets. Recently, anti-FGF23 antibody, burosumab, has become clinically available. We herein report a patient with adult XLH and tertiary hyperparathyroidism.

CASE PRESENTATION

The serum phosphate level and tubular maximum reabsorption of phosphate per glomerular filtration rate (TmP/GFR) remained low, despite burosumab treatment. While the influence of the relationship between FGF23 and parathyroid hormone (PTH) on the phosphaturic effect is unclear, it was considered that a high level of PTH due to tertiary hyperparathyroidism remains to suppress renal phosphate reabsorption. A calcimimetic, evocalcet, increased the serum phosphate level and TmP/GFR.

DISCUSSION AND CONCLUSION

Therefore, it is important to evaluate the presence of secondary-tertiary hyperparathyroidism in patients whose serum phosphate level does not increase with burosumab treatment.

Renal Phosphate Handling: Independent Effects of Circulating FGF23, PTH, and Calcium

Excess fibroblast growth factor 23 (FGF23), excess PTH, and an increase in extracellular calcium cause hypophosphatemia by lowering the maximum renal phosphate reabsorption threshold (TmP/GFR). We recently reported two cases of X-linked hypophosphatemia (XLH) with severe tertiary hyperparathyroidism who had normalization of TmP/GFR upon being rendered hypoparathyroid following total parathyroidectomy, despite marked excess in both C-terminal FGF23 (cFGF23) and intact FGF23 (iFGF23). We explored the effects of FGF23, PTH, and calcium on TmP/GFR in a cross-sectional study (n = 74) across a spectrum of clinical cases with abnormalities in TmP/GFR, PTH, and FGF23. This comprised three groups: FGF23-dependent hypophosphatemia (n = 27), hypoparathyroidism (HOPT; n = 17), and chronic kidney disease (n = 30). Measurements included TmP/GFR, cFGF23, PTH, ionized calcium, vitamin D metabolites, and bone turnover markers. The combined effect of cFGF23, PTH, and ionized calcium on TmP/GFR was modeled using hierarchical multiple regression and was probed by moderation analysis with PROCESS. Modeling analysis showed independent effects on TmP/GFR by cFGF23, PTH, and ionized calcium in conjunction with a weak but significant effect of the interaction term for PTH and FGF23; probing showed that the effect was most prominent during PTH deficiency. Teriparatide 20 μg daily was self-administered for 28 days by one case of X-linked hypophosphatemia with hypoparathyroidism (XLH-HOPT) to assess the response of TmP/GFR, cFGF23, iFGF23, nephrogenous cyclic adenosine monophosphate (NcAMP), vitamin D metabolites, and bone turnover markers. After 28 days, TmP/GFR was lowered from 1.10 mmol/L to 0.48 mmol/L; this was accompanied by increases in NcAMP, ionized calcium, and bone turnover markers. In conclusion, the effect of FGF23 excess on TmP/GFR is altered by PTH such that the effect is ameliorated by hypoparathyroidism and the effect is augmented by hyperparathyroidism. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Anorexia Nervosa with Markedly High Bone Turnover and Hyperphosphatemia During Refeeding Rectified by Denosumab

We describe a unique case of hyperphosphatemia associated with a very high bone turnover rate in a 51-year-old postmenopausal woman with undiagnosed anorexia nervosa (AN) who presented with a low-trauma hip fracture. In view of her severely malnourished state, she was not fit for surgery. She was treated according to a refeeding protocol that mandated bed rest. Contrary to expectation, she developed sustained hyperphosphatemia and borderline hypercalcemia. Bone remodelling markers, both resorption and formation, were markedly elevated. Parathyroid hormone (PTH) was low-normal at 1.7 pmol/L, C-terminal fibroblast growth factor 23 (FGF23) was high at 293 RU/ml, but tubular maximum reabsorption of phosphate (TmPO4/GFR) was elevated at 1.93 mmol/L. Denosumab 60 mg was administered that was followed by: rapid normalisation of serum phosphate; normalisation of resorption markers, transient hypocalcaemia with secondary hyperparathyroidism, and normalisation of both TmPO4/GFR and C-terminal FGF23. We speculate that prolonged immobilization as part of AN management led to a high remodelling state followed by hyperphosphatemia and high-normal calcium with appropriate suppression of PTH and that marked hyperphosphatemia and high TmP/GFR despite high FGF23 indicates the necessity of PTH adequacy for excess FGF23 to lower TmP/GFR.

Congenital hypophosphataemia in adults: determinants of bone turnover markers and amelioration of renal phosphate wasting following total parathyroidectomy

Congenital hypophosphataemia (CH) is a collection of disorders that cause defective bone mineralisation manifesting with rickets in childhood and osteomalacia in adulthood. Bone turnover markers (BTMs) are surrogate measures of metabolic bone disease severity. We explored the utility of BTMs in 27 adults with CH: 23 had X-linked hypophosphataemia (XLH), of whom 2 were hypoparathyroid post-total parathyroidectomy (PTx); 2 had autosomal dominant hypophosphataemic rickets (ADHR), and 2 had none of the known mutations. We measured the renal tubular maximum reabsorption rate of phosphate (TmP/GFR), C-terminal fibroblast growth factor 23 (FGF23), parathyroid hormone (PTH), ionised calcium, 1,25-dihydroxyvitamin D [1,25(OH)₂D], and a panel of BTMs: serum bone-specific alkaline phosphatase (bone ALP), osteocalcin (Oc), total procollagen type I amino-terminal propeptide (PINP), and carboxy-terminal telopeptide of type I collagen (CTX); and urine amino-terminal telopeptides of type I collagen (uNTX). After excluding 2 patients with XLH and PTx, the frequency of abnormal elevation in BTMs was: bone ALP (96%); CTX (72%); PINP (52%); uNTX (48%); Oc (28%). The strongest association with bone ALP was TmP/GFR. Those patients receiving phosphate supplements and alfacalcidol had significant elevation in CTX. The 2 patients with XLH and PTx had normalisation of TmP/GFR and near normalisation of BTMs post-operatively, despite marked elevation in both C-terminal and intact FGF23. In conclusion, BTMs in our CH patients indicated that most have abnormalities consistent with osteomalacia and many have mild secondary hyperparathyroidism; and the normalisation of TmP/GFR after total PTx in 2 cases of XLH remains unexplained, but possible causes are speculated.

Developments in rare bone diseases and mineral disorders

In the last decade, there have been a number of significant advances made in the field of rare bone diseases. In this review, we discuss the expansion of the classification system for osteogenesis imperfecta (OI) and the resultant increase in therapeutic options available for management of OI. Bisphosphonates remain the most widely used intervention for OI, although the effect on fracture rate reduction is equivocal. We review the other therapies showing promising results, including denosumab, teriparatide, sclerostin, transforming growth factor β inhibition and gene targeted approaches. X-linked hypophosphataemia (XLH) is the most common heritable form of osteomalacia and rickets caused by a mutation in the phosphate regulating endopeptidase gene resulting in elevated serum fibroblast growth factor 23 (FGF23) and decreased renal phosphate reabsorption. The traditional treatment is phosphate replacement. We discuss the development of a human anti-FGF23 antibody (KRN23) as a promising development in the treatment of XLH. The current management of primary hypoparathyroidism is replacement with calcium and active vitamin D. This can be associated with under or over replacement and its inherent complications. We review the use of recombinant parathyroid hormone (1-84), which can significantly reduce the requirements for calcium and vitamin D resulting in greater safety and quality of life for individuals with hypoparathyroidism. The use of receptor activator of nuclear factor κB ligand infusions in the treatment of a particular form of osteopetrosis and enzyme replacement therapy for hypophosphatasia are also discussed.

Atypical Parathyroid Adenoma Complicated with Protracted Hungry Bone Syndrome after Surgery: A Case Report and Literature Review

Hungry Bone Syndrome refers to the severe and prolonged hypocalcemia and hypophosphatemia, following parathyroidectomy in patients with hyperparathyroidism. We present the case of an eighteen-year-old woman with a four-year history of hyporexia, polydipsia, weight loss, growth retardation, and poor academic performance. The diagnostic work-up demonstrated primary hyperparathyroidism with hypercalcemia of 13.36 mg/dL, a PTH level of 2551 pg/mL, bone brown tumors, and microcalcifications within pancreas and kidneys. Neck ultrasonography revealed a parathyroid adenoma of 33 × 14 × 14 mm, also identified on (99)Tc-sestamibi scan. Bone densitometry showed decreased Z-Score values (total lumbar Z-Score of -4.2). A right hemithyroidectomy and right lower parathyroidectomy were performed. Pathological examination showed an atypical parathyroid adenoma, of 3.8 g of weight and 2.8 cm in diameter. After surgery she developed hypocalcemia with tetany and QTc interval prolongation. The patient required 3 months of oral and intravenous calcium supplementation due to Hungry Bone Syndrome (HBS). After 42 months, she is still under oral calcium. Usually HBS lasts less than 12 months. Therefore we propose the term "Protracted HBS" in patients with particularly long recovery of 1 year. We present a literature review of the diagnosis, pathophysiology, and treatment of HBS.