Familial benign (hypocalciuric) hypercalcemia. A troublesome mimic of mild primary hyperparathyroidism

Familial benign hypercalcemia, or hypocalciuric hypercalcemia, may be defined as a dominantly inherited disorder of calcium and magnesium metabolism, characterized by lifelong hypercalcemia and hypermagnesemia (both of variable degree), that usually is not associated with any symptoms, physical signs, reduced vitality, or ill health. Chondrocalcinosis, pancreatitis, gallstones, and neonatal primary hyperparathyroidism are possible rare associations, but findings differ among various studies. The biochemical findings are bland, with "normal" values for serum PTH by many techniques, modest hypophosphatemia, and other findings usually normal. A low calcium:creatinine clearance ratio is suggestive of, but not diagnostic for, FBH; urinary calcium excretion less than 100 mg per day may be just as helpful. The diagnosis should not be made casually or without family screening, because the findings in a given patient may be identical to those in mild primary hyperparathyroidism. The major rationale for careful evaluation is to diagnose the syndrome of FBH and to help affected family members avoid needless expense and the risk of further evaluation and treatment.