A 20-year-old man is found to have an elevated calcium level on pre-employment screening blood tests. He feels well and has no polyuria, polydipsia, or constipation. His medical history is unremarkable. He takes no prescription medications, although he has been consuming "protein shakes and vitamin supplements" in preparation for running a marathon. The patient does not use tobacco, alcohol, or illicit drugs. Temperature is 37 C (98.6 F), blood pressure is 110/70 mm Hg, and pulse is 82/min. Physical examination is unremarkable. Laboratory results are as follows: Which of the following conditions is most consistent with this patient's findings?

Question

A 20-year-old man is found to have an elevated calcium level on pre-employment screening blood tests.  He feels well and has no polyuria, polydipsia, or constipation.  His medical history is unremarkable.  He takes no prescription medications, although he has been consuming "protein shakes and vitamin supplements" in preparation for running a marathon.  The patient does not use tobacco, alcohol, or illicit drugs.  Temperature is 37 C (98.6 F), blood pressure is 110/70 mm Hg, and pulse is 82/min.  Physical examination is unremarkable.  Laboratory results are as follows:  Which of the following conditions is most consistent with this patient's findings?

Quizplus · Accepted Answer

11ec25c8_d4df_8d60_bc81_7b3525dfba06_MD0003_00 This patient has mild, asymptomatic hypercalcemia and normal renal function. In light of a high-normal parathyroid hormone (PTH) level and low urinary calcium excretion, this presentation is consistent with familial hypocalciuric hypercalcemia (FHH). FHH is a benign autosomal dominant disorder caused by a mutation of the calcium-sensing receptor (CaSR). Normally, high-normal calcium levels suppress PTH secretion by the parathyroid glands, but in FHH, higher calcium concentrations are required to suppress PTH release. Concurrently, the defective CaSR leads to increased reabsorption of calcium in renal tubules. In the evaluation of hypercalcemia, an elevated (or inappropriately normal) PTH level suggests either primary hyperparathyroidism or FHH. However, patients with primary hyperparathyroidism have increased urinary calcium excretion due to excessive mobilization of calcium from bones, whereas patients with FHH usually have very low urinary calcium levels (typically <100 mg/24 hr). Urine calcium excretion can be more precisely assessed using the urine calcium/creatinine clearance ratio (UCCR): UCCR = (Ca_urine/Ca_serum)STRONG_(Creat_urine/Creat_serum) _urine _serum _urine _serum UCCR is usually <0.01 in FHH compared to >0.02 in primary hyperparathyroidism (Choice C). Most patients with FHH are asymptomatic, although potential complications include pancreatitis and chondrocalcinosis. In the absence of complications, no specific treatment is required. (Choices B, D, E, and F) Patients with multiple myeloma, renal cell carcinoma, sarcoidosis, and vitamin D toxicity may also present with hypercalcemia, but PTH levels are typically suppressed due to feedback inhibition. Educational objective: Familial hypocalciuric hypercalcemia is caused by a mutation in the calcium-sensing receptor. It is a benign disorder characterized by asymptomatic hypercalcemia, elevated or inappropriately normal parathyroid hormone levels, and low urinary calcium excretion. It can be differentiated from primary hyperparathyroidism, which has increased urinary calcium excretion, by the urine calcium/creatinine clearance ratio. References: Familial hypocalciuric hypercalcaemia: a review. (http://www.ncbi.nlm.nih.gov/pubmed/21986511)

A 20-Year-Old Man Is Found to Have an Elevated Calcium