Endocrine Abstracts

Introduction: Primary hyperparathyroidism (HPTH) and familial hypocalciuric hypercalcemia (FHH) are two important differential diagnoses for high calcium with non-suppressed parathyroid hormone (PTH). In this case report, we would like to present an unusual cause of hypercalcemia.

Clinical case: A 68-year-old lady was seen in endocrine clinic for hypercalcemia with normal PTH. She reported fatigue, depression, and abdominal pain intermittently but denied polyuria, polydipsia, or thyroid disease. She was diagnosed with FHH in her thirties. She denied taking Vitamin D, calcium supplements or family history of FHH.

Investigations: The adjusted calcium ranges from 2.86 to 3.06 mmol/L (2.2 - 2.6) with non-suppressed PTH. Her initial urine calcium creatinine clearance ratio (UCCCR) was 0.0056. Her vitamin D was 66nmol/L. The ultrasound of the urinary tract was unremarkable. Her bone density showed osteopenia at the femoral neck. The Sestamibi scan and the ultrasound parathyroid failed to localize an adenoma.

Management: She attended ambulatory care twice for hypercalcemia of more than 3mmol/L that required treatment. She was discussed in a multidisciplinary team (MDT) meeting, which recommended the low UCCCR was suggestive of FHH whereas the calcium of 3.01mmol/L was more in favour of HPTH. The plan was to repeat UCCCR, replete vitamin D, to send genetic testing for FHH and perform a 4D CT neck. Vitamin D was replaced. The genetic testing confirmed CASR gene-related FHH. The CT neck revealed a 6mm nodule that is highly suggestive of a left inferior parathyroid adenoma and a 3mm possible right parathyroid adenoma. She was discussed again in the MDT meeting and was referred to a tertiary centre for further management given dual pathology.

Conclusion: This rare case highlighted that one needs to be vigilant of the possibility of concurring FHH and primary hyperparathyroidism when calcium level is disproportionate to UCCCR.