Familial Hypocalciuric Hypercalcemia and Primary Hyperparathyroidism in the Same Patient

Primary hyperparathyroidism is the main cause of hypercalcemia while familial hypocalciuric hypercalcemia is a rare one. We report a case of a 39-year-old woman followed at our rheumatology outpatient center with the diagnosis of ankylosing spondylitis in which the routine laboratorial analysis demonstrated hypercalcemia with high levels of parathyroid hormone. The ultrasound, scintigraphy, and histology findings confirmed the diagnosis of primary hyperparathyroidism and parathyroid hyperplasia as the underlying cause. After surgery, given the persistence of hypercalcemia in association with a low urinary calcium excretion, a genetic study was carried out which led to the diagnosis of familial hypocalciuric hypercalcemia type 1. The patient had no symptoms or familiar history of hypercalcemia. The authors highlight the rarity of the association of these two conditions in the same patient and the importance of considering familial hypocalciuric hypercalcemia as a possible diagnosis even in patients with an established diagnosis of primary hyperparathyroidism.