Hypercalcaemia and hyperparathyroidism — structured clinical encounter

Station brief (candidate)

You are the paediatric registrar. A 14-year-old boy presents with six months of renal colic, bone pain and fatigue. 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 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. The team asks you to confirm the diagnosis, arrange the remaining investigations, plan the treatment, and speak with the family. You have 12 minutes with the team and 5 minutes for examiner discussion. [4]

Information available on request

• 14-year-old boy; renal colic, bone pain, fatigue over six months; no weight loss or palpable mass. [4]
• Corrected calcium 2.9 mmol per litre; phosphate low; alkaline phosphatase mildly raised; renal function normal. [4]
• Intact parathyroid hormone inappropriately normal (not suppressed) despite the high calcium. [1]
• Urine calcium-to-creatinine clearance ratio 0.02 (above 0.01); 25-hydroxyvitamin D mildly low. [6]
• Sestamibi single-photon emission computed tomography: a single focus of uptake at the lower left pole of the thyroid; neck ultrasound concordant. [2]

Tasks

1. State the most likely diagnosis and explain why the parathyroid hormone is inappropriately normal rather than suppressed. [4]
2. Name the test that separates this condition from familial hypocalciuric hypercalcaemia and its cut-off, and explain why the distinction matters. [6]
3. Describe the definitive treatment and the intraoperative monitoring that confirms cure. [1]
4. State the complication you must anticipate after surgery and communicate the plan in plain language to the family. [4]

Marking anchors

Must-hit

• Diagnoses primary hyperparathyroidism from a single parathyroid adenoma, and explains that the autonomous adenoma secretes parathyroid hormone regardless of the calcium level, so the hormone is inappropriately normal rather than suppressed. [4]
• Identifies the urine calcium-to-creatinine clearance ratio as the separating test (above 0.01 = primary hyperparathyroidism, below 0.01 = familial hypocalciuric hypercalcaemia), and states that the distinction matters because operating on familial hypocalciuric hypercalcaemia recurs and causes permanent hypocalcaemia. [6]
• Plans a focused parathyroidectomy guided by preoperative localisation, with intraoperative parathyroid hormone monitoring in which a fall of more than fifty percent into the normal range at ten minutes confirms cure; screens for multiple endocrine neoplasia. [1]
• Anticipates hungry bone syndrome — severe hypocalcaemia as calcium floods into the demineralised skeleton — and plans oral calcium and calcitriol with intravenous calcium ready, monitoring every six to twelve hours. [4]

Merit

• Explains that a single adenoma accounts for roughly eighty percent of paediatric primary hyperparathyroidism, and that children are more often symptomatic than adults, so surgery is offered more liberally. [4]
• Counsels the family in plain language: this is a small hormone-producing gland that has become overactive, the operation removes it, the calcium will fall, and the child will need calcium tablets for a while afterwards because the bone takes up calcium rapidly. [4]
• Places the case in context: primary hyperparathyroidism is rare in children but curable in the great majority with expert surgery, and the family should be screened for the multiple endocrine neoplasia genes because the syndromic form needs a different operation. [5]

Fail

• Reassures the family that the calcium is benign and does not investigate further, missing the symptomatic primary hyperparathyroidism and the curative surgery. [4]
• Orders parathyroid surgery without checking the urine calcium-to-creatinine clearance ratio, risking an operation on familial hypocalciuric hypercalcaemia that recurs and causes hypocalcaemia. [6]
• Plans surgery without arranging postoperative calcium monitoring or replacement, leaving the child to develop symptomatic hungry bone syndrome. [4]