Endocrine Abstracts

Background: Hungry bone syndrome (HBS) is a prolonged and profound post-operative hypocalcaemic state following parathyroidectomy or thyroidectomy. The incidence is uncommon, cited between 4-13% with surgically treated primary hyperparathyroidism, and can last up to a year post-operatvely. Hypocalcaemia in HBS (usually <2.1 mmol/l) is rapid, and is attributed to the sudden decline in parathyroid hormone (PTH) levels which alters the milieu of PTH-mediated osteoclastic bone resorption in patients with uncontrolled primary hyperparathyroidism, towards osteoblast-mediated bone resorption. The subsequent influx of minerals into the skeleton leads to hypocalcaemia, hypomagnesaemia and hypophosphataemia. This is further accentuated by the failure of the remaining suppressed parathyroid glands to regain activity for a period of time. The spectrum of HBS symptoms includeparaesthesia, tetany, arrhythmias, cardiomyopathy, and seizures.

Clinical case: A 32-year-old fit-and-well man presents to his GP with chronic, non-specific back and knee pain. He was found to have incidental severe hypercalcaemia (3.75 mmol/l (NR 2.20-2.60 mmol/l), leading to hospital admission. Further stratitificaiton showed severe primary hyperparathyroidism (PTH:227 pmol/l; N=1.6-6.1 pmol/l)ALP of 1578 u/l, and 25-OH vitamin D insufficient 26 nmol/l. NM parathyroid SPECT CT showed a left intrathyroid parathyroid adenoma measuring 3.1 × 2.5 × 4.6 cm. CT-NCAP was also consistent with this, alongside evidence of erosive bone disease at the sacroiliac joints, iliac wings and left humeral head. After immediate management with IV hydration, he underwent left thyroidectomy with parathyroidectomy, with marked intra-operative PTH reduction to 9.9 pmol/l. recalcitrant hypocalcaemia over 3 weeks as inpatient (corrected calcium 1.70-1.95 mmol/l) with associated symptoms of hypocalcaemia which was refractory to treatment. Subsequent histology showed parathyroid carcinoma currently awaits head and neck MDT outcomes.

Specific management: Management of HBS constitutes careful monitoring and replacement of depleted electrolytes. Severe hypocalcaemia <1.9 mmol/l, symptomatic hypocalcaemia, or ECG changes such as QTc prolongation indicate the need for IV calcium replacement. Activate 1,25(OH)2 cholecalferol (Calcitriol) is the treatment of choice since it does not need any PTH activity for hydroxylation. Subsequently IV calcium can be replaced with high dose oral elemental calcium. Careful monitoring at 2-weekly intervals is required to prevent rebound hypercalcaemia when the remaining parathyroid glands start responding.

Learning points: • HBS is a serious complication of parathyroidectomy following severe untreated primary hyperparathyroidism (PHPT) and is characterised by a profound and prolonged period of hypocalcaemia.• Adequate history regarding duration and severity of PHPT is necessary to guide post-operative management.• Management of post-operative hypocalcaemia requires IV replacement if: severe <1.9 mmol/l, symptomatic, or associated with ECG changes alongwith Calcitriol• Careful monitoring of bloods and dose titration of calcium replacement is indicated both in the peri-operative and post-operative periods