Hypercalcaemia and hyperparathyroidism — formative SAQs

SAQ 1 — The adolescent with stones and bone pain (20 marks, ~15 minutes)

A 14-year-old boy presents with renal colic, bone pain and fatigue over six months. His corrected calcium is 2.9 mmol per litre, his phosphate is low, and his intact parathyroid hormone is inappropriately normal rather than suppressed. A spot urine calcium-to-creatinine clearance ratio is 0.02. A sestamibi scan shows a single focus of uptake at the lower left pole of the thyroid. ^[4]

Questions

1. Give the most likely diagnosis and explain why the parathyroid hormone is inappropriately normal rather than suppressed. (4 marks) ^[4]
2. Outline the confirmatory and localising work-up, naming the test that separates this condition from familial hypocalciuric hypercalcaemia and its cut-off. (5 marks) ^[2]
3. Describe the definitive treatment and the intraoperative monitoring that confirms cure. (5 marks) ^[1]
4. State the complication you must anticipate in the first days after surgery and how you manage it. (6 marks) ^[4]

Model answer (must-hit)

1. This is primary hyperparathyroidism from a single parathyroid adenoma. The calcium is high, yet the parathyroid hormone is not suppressed, because the autonomous adenoma secretes hormone regardless of the calcium level — the feedback brake is broken, so the hormone is inappropriately normal or high. The low phosphate reflects the phosphaturic effect of the parathyroid hormone on the renal tubule. ^[4]
2. Confirm the calcium with an albumin correction or ionised value, then measure intact parathyroid hormone (inappropriately normal confirms PTH-dependent disease). The test that separates this from familial hypocalciuric hypercalcaemia is the urine calcium-to-creatinine clearance ratio: above 0.01 means primary hyperparathyroidism, below 0.01 means familial hypocalciuric hypercalcaemia. This child's ratio of 0.02 points to primary hyperparathyroidism. Localise the gland with a sestamibi single-photon emission computed tomography scan and a neck ultrasound, correct any vitamin D deficiency, and screen for the multiple endocrine neoplasia genes. ^[2]
3. The definitive treatment is a focused parathyroidectomy to remove the adenoma, guided by preoperative localisation and intraoperative parathyroid hormone monitoring. A hormone fall of more than fifty percent into the normal range at ten minutes after excision confirms cure. Screen the family for multiple endocrine neoplasia because multigland hyperplasia needs a subtotal or total parathyroidectomy rather than a focused removal. ^[1]
4. Anticipate hungry bone syndrome. The sudden removal of parathyroid hormone lets calcium flood into the demineralised skeleton, producing severe and sometimes symptomatic hypocalcaemia within hours to days. Monitor the calcium every six to twelve hours, give oral calcium and calcitriol prophylactically, and have intravenous calcium ready. The low calcium is the sign that the operation worked, not that it failed. ^[4]