A 22-year-old man comes to the office to discuss laboratory test results. He is a competitive cross-country skier and is required to have periodic blood testing to comply with international rules. The patient feels well except for occasional heartburn for which he takes antacids. He trains strenuously on a regular basis and is on a very high protein diet. The patient's medical history is unremarkable except for a concussion at age 17; at that time, his serum calcium was noted to be borderline high, but the patient did not follow up with his physician after discharge from the hospital. His father was also found to have hypercalcemia at a young age but has not required any specific treatment and is otherwise healthy. The patient takes no prescription medications and does not use tobacco, alcohol, or illicit drugs. Laboratory results are as follows: Which of the following clinical findings is most likely present in this patient?

Question

A 22-year-old man comes to the office to discuss laboratory test results.  He is a competitive cross-country skier and is required to have periodic blood testing to comply with international rules.  The patient feels well except for occasional heartburn for which he takes antacids.  He trains strenuously on a regular basis and is on a very high protein diet.  The patient's medical history is unremarkable except for a concussion at age 17; at that time, his serum calcium was noted to be borderline high, but the patient did not follow up with his physician after discharge from the hospital.  His father was also found to have hypercalcemia at a young age but has not required any specific treatment and is otherwise healthy.  The patient takes no prescription medications and does not use tobacco, alcohol, or illicit drugs.  Laboratory results are as follows:  Which of the following clinical findings is most likely present in this patient?

Quizplus · Accepted Answer

Explanation: This patient has mild (eg, <12 mg/dL), asymptomatic hypercalcemia. In light of his chronic course, normal renal function, and family history of benign hypercalcemia, this is most likely due to familial hypocalciuric hypercalcemia (FHH), an autosomal dominant disorder due to inactivating mutations of the calcium-sensing receptor. Normally, high-normal calcium levels suppress parathyroid hormone (PTH) secretion, but in FHH, higher calcium concentrations are required to suppress PTH release. Concurrently, the defective calcium-sensing receptor causes increased reabsorption of calcium in renal tubules. higher calcium concentrations The first step in evaluation of hypercalcemia is to measure PTH; patients with FHH typically have high-normal PTH levels. FHH can then be differentiated from primary hyperparathyroidism by measurement of urinary calcium excretion, which will be elevated in hyperparathyroidism and low in FHH. Patients with FHH have no clinical findings and no treatment is necessary. (Choices A and B) Chvostek sign (contraction of the facial muscles when the facial nerve is tapped) and hyperreflexia are features of hypocalcemia, not hypercalcemia. (Choices D and E) Patients (and family members) with multiple endocrine neoplasia (MEN) types 1 and 2A may present with hypercalcemia due to primary hyperparathyroidism. However, they are less likely than patients with FHH to follow a benign course and usually have additional features. MEN 1 also causes pituitary tumors (eg, visual field defects) and enteropancreatic neuroendocrine tumors, whereas MEN 2A also causes medullary thyroid cancer (palpable neck mass) and pheochromocytoma. FHH does not affect the pituitary gland or cause palpable parathyroid findings. Educational objective: Familial hypocalciuric hypercalcemia is an autosomal dominant disorder due to inactivating mutations of the calcium-sensing receptor. Patients with familial hypocalciuric hypercalcemia have mild hypercalcemia without any clinical findings and do not require any treatment. References: Familial hypocalciuric hypercalcaemia: a review. (http://www.ncbi.nlm.nih.gov/pubmed/21986511)

A 22-Year-Old Man Comes to the Office to Discuss Laboratory