Endocrine Abstracts

Introduction: Hypercalcaemia diagnosed in hospital setting is most commonly PTH-independent and malignancy related, whilst hypercalcaemia discovered in community setting is commonly secondary to Primary Hyperparathyroidism (PHPT). Other rare causes include granulomatous diseases such as sarcoidosis and familial hypocalciuric hypercalcaemia (FHH).

Case Summary: A 73-year-old male with a background of hypertension and chronic kidney disease stage 3 was found to be hypercalcaemic on routine blood tests by his GP. He had no symptom of hypercalcaemia and his CXR demonstrated bilateral lower zone opacifications. He was admitted to hospital with an adjusted serum calcium of 3.03 mmol/l (NR 2.2 – 2.6) and an eGFR of 53 mL/min/1.73m2. He received intravenous Zoledronic acid and was referred to the Endocrine team for follow-up. His serum vitamin D level was low at 35 nmol/l and his PTH was 5.6 pmol/l (NR 1.1 – 6.4). He received a loading dose of oral vitamin D (100,000 units) followed by daily replacement dosing. His adjusted serum calcium level remained elevated, varying between 2.87 and 3.13 mmol/l, with a suppressed serum phosphate level at 0.51 mmol/l (NR 0.8 – 1.5). His fractional urine calcium excretion, based on a 24 hour urine collection, remained low at 1%, despite vitamin D supplementation. By that time CT imaging of his chest demonstrated features suggestive of pulmonary sarcoidosis. His serum angiotensin converting enzyme level was normal. Given the level of persistent hypercalcaemia, functional imaging of the parathyroid was undertaken which demonstrated a 1.1 cm enhancing nodule posterior to the lower pole of the right lobe of the thyroid suggestive of a parathyroid adenoma. His persistently low urine calcium excretion prompted genetic testing for FHH which revealed a monoallelic pathogenic calcium-sensing receptor (CASR) variant on chromosome 3.

Discussion: Our case highlights the importance of investigating for FHH in patients with PTH-dependent hypercalcaemia and persistently low urine calcium excretion despite replete vitamin D levels. What is unique in our patient is the coexisting diagnosis of sarcoidosis and probable PHPT. To what extent these two diagnoses are influencing his serum calcium level remain unclear. Nevertheless our patient remains asymptomatic from his hypercalcaemia with no evidence of end-organ damage on bone density scan and renal imaging.