Endocrine Abstracts

Introduction: Familial hypocalciuric hypercalcemia (FHH) is a benign condition characterized by asymptomatic hypercalcemia secondary to hypocalciuria. Affected patients have variable parathyroid hormone levels. It is caused by a loss-of-function mutation in the calcium-sensing receptor (CASR) gene. The occurrence of both FHH and primary hyperparathyroidism (PHPT) in the same patient has rarely been described. We report an interesting case.

Case: A 71-year-old lady was reviewed because of severe hypercalcaemia. This was discovered during routine screening because of a family history of FHH and the presence of the CASR gene mutation. She was asymptomatic. She had no relevant past medical history and was not taking any medication.

Investigation and management: Blood results indicated mild chronic kidney disease and normal vitamin D levels, raised serum calcium (3.24 mmol/l), low serum phosphate (0.67 mmol/l) and a slightly raised parathyroid hormone (PTH: 11.9 pmol/l). Her 24-hour urinary calcium was inappropriately low at 2.2 mmol/24hr, confirming hypocalciuria. Genetic testing confirmed the presence of the CASR gene mutation [c.2444A>G, p.(Lys815Arg)]. However, the disproportionately high serum calcium level prompted further investigation. Her bone density scan showed osteopenia. An ultrasound and parathyroid MIBI scan detected a right lower pole parathyroid adenoma. After informed discussion she underwent parathyroidectomy (histology confirmed a parathyroid adenoma). Postoperatively her calcium fell down to 2.51 mmol/l and then rose to 2.78 mmol/l. PTH fell to 0.8 pmol/l then rose to 7.4pmol/L. Current serum calcium levels remains at 2.72 mmol/l with a calcium-creatinine clearance of 0.005, indicating continued mild hypercalcaemia of FHH.

Conclusion: The coexistence of FHH and PHPT should be considered in patients with hypercalcemia, hypophosphatemia, mildly elevated parathyroid hormone levels and inappropriate hypocalciuria. Although surgical intervention may not resolve the hypercalcemia completely, it will alleviate the symptoms and prevent potential complications of the hypercalcaemia secondary to PHPT.