Endocrine Abstracts

A 29-year-old-female presented to the emergency department with a 4 week history of polyuria, polydipsia and night sweats. Her adjusted calcium (Aca) was elevated at 3.12 mmol/L (2.2-2.6). Clinical examination was unremarkable. Her past medical history included migraines. There was no relevant family history. Repeat biochemistry showed an ACa 3.14 mmol/l, phosphate of 0.55 mmol/L (0.8-1.5), parathyroid hormone (PTH) of 8.4 pmol/l (3.1-6.8), eGFR > 90 and Vitamin D of 45nmol/l (51-163). Her ACa remained at 3.03 mmol/L despite intravenous fluids. Given the significantly raised ACa and osmotic symptoms, she was started on calcimimetic Cinacalcet 30 mg twice daily for suspected primary hyperparathyroidism (PHPT), with improvement in her symptoms and biochemistry (including normalisation of PTH). Parathyroid imaging and DEXA were unremarkable. Her 24 hour urinary calcium creatinine ratio was low at 0.0092, and remained low at 0.0021 when repeated off Cinacalcet. Genetic screening revealed heterogenicity of the calcium sensing receptor (CaSR) missense variant, confirming Familial Hypocalciuric Hypercalcaemia (FHH) Type 1. She was restarted on Cinacalcet 30 mg twice daily and her latest ACa was 2.61 mmol/l. She is tolerating Cinacalcet well though reports occasional muscle cramps and paraesthesia. FHH causes lifelong hypercalcaemia similar to that of PHPT. The former is often asymptomatic or mildly symptomatic without increased risk of complications such as renal calculi and osteoporosis favouring conservative management over pharmacological or surgical approaches. Recent case reports suggest calcimimetics may have a role in FHH where ACa is persistently raised > 0.25mmol/L above the upper limit of normal or if symptomatic, with subjective and biochemical improvement defining treatment success. This case demonstrates successful treatment with Cincacalet, with few adverse effects, suggesting allosteric modulation of CaSR with Cinacalcet may have a role in FHH. Long-term follow up and randomised controlled trials are needed to explore its potential.