Recurrent hungry bone syndrome in a kidney transplant recipient with a history of parathyroidectomy: A case report

Background: The hungry bone syndrome (HBS) is a well described phenomenon occurring shortly after parathyroidectomy characterized by rapid bone formation with concomitant hypocalcemia, hypophosphatemia and hypomagnesemia requiring intensive management. Recurrent HBS occurring in isolation from parathyroidectomy has not been reported.

Case presentation: We describe a case of recurrent HBS in a kidney transplant recipient (KTR) developing years after parathyroidectomy. The KTR was a 49 year-old lady who had undergone successful total parathyroidectomy without re-implantation 14 years prior and cadaveric kidney transplantation 12 years prior. She had a stable creatinine level of 220μmol/L and an estimated glomerular filtration rate (eGFR) of 20 mL/min^-1.73m². She presented to us with severe hypercalcemia, likely a result of excessive calcium and vitamin D supplementation, and acute kidney injury. Serum creatinine, calcium, phosphate, magnesium, alkaline phosphatase (ALP), and intact parathyroid hormone (iPTH) levels on admission were 743μmol/L, 4.8 mmol/L, 1.8 mmol/L, 0.75 mmol/L, 48IU/L and <0.1 pmol/L, respectively. Vigorous intravenous fluids were given in addition to withdrawal of calcium carbonate and calcitriol. Clinical improvement was evident with falling serum creatinine and calcium levels. However, this was followed 2–3 days after admission by an unexplained rise in ALP from a baseline of 48IU/L to a peak level of 1150IU/L over the next week, accompanied by the development of severe hypocalcemia, hypomagnesemia and a persistent drop in phosphate levels. The patient required large doses of calcium carbonate, calcitriol and magnesium lactate to maintain blood mineral levels. The ALP progressively decreased subsequently and the serum levels of calcium, phosphate and magnesium began to stabilize in the next 2–3 weeks.

Conclusion: Recurrent HBS can occur years after parathyroidectomy in KTRs. We hypothesize that hypercalcemia and its rapid correction might have been the trigger in this particular patient. The mechanism is not well understood but might involve bone remodeling pathways that are independent of parathyroid hormone.