Endocrine Abstracts

Introduction: There are reports of patients having co-existing primary hyperparathyroidism and familial hypocalciuric hypercalcaemia (FHH). The combination of relative hypocalciuria, hypercalcaemia and slightly elevated serum parathyroid hormone (PTH) could indicate FHH. Medications such as, lithium and bendroflumethiazide can reduce renal excretion of calcium. We report a case highlighting the importance of being aware of drug-induced hypocalciuria during the investigation of hypercalcaemia.

Case: A 69-year-old woman had mild tiredness for several years. Routine test revealed hypercalcaemia. She had no other symptoms. Medical history included type 2 diabetes, hypertension, atrial fibrillation and psoriasis. Medication list consisted of amlodipine, metformin, atorvastatin, digoxin, losartan, bendroflumethiazide and warfarin. She had no previous calcium levels for comparison.

Investigations and management: Her serum calcium was 2.85 mmol/l with a slightly elevated PTH of 7.3 pmol/l. Serum phosphate, magnesium, vitamin-D, renal and liver function, angiotensin-converting enzyme and electrophoresis were normal. Full blood count and erythrocyte sedimentation rate was normal. Urine protein was normal. A 24-hour urinary calcium of 1.6 mmol/24h indicated relative hypocalciuria, suggesting possible FHH. Her calculated calcium-creatinine clearance ratio (CCCR) was also low (0.0009) with serum calcium of 3.04 mmol/l. A parathyroid ultrasound was negative, but a nuclear medicine scan demonstrated increased uptake in the right thyroid lobe. Kidney ultrasound scan was normal. Bone density scan revealed slightly low levels in the hip only. On stopping the bendroflumethiazide, her CCCR increased to 0.0163 and 0.0183 (serum calcium: 2.77 mmol/l and 2.89 mmol/l, respectively). Her 24-hour urinary calcium increased to 7.5 mmol/24h. A repeat serum calcium was 2.92 mmol/l, while serum PTH fell to 4.7 pmol/l. A subsequent 4-dimensional CT scan revealed two discreet nodules suggestive of parathyroid adenomas.

Conclusion: This case report emphasizes the importance of stopping bendroflumethiazide before assessing urinary calcium excretion during the investigation of hypercalcaemia.