Acquired hypocalciuric hypercalcemia in a dog

A 12-year-old castrated male Labrador Retriever presented with asymptomatic hypercalcemia. Based on elevated parathyroid hormone levels and an enlarged parathyroid gland, primary hyperparathyroidism was suspected, and parathyroidectomy was performed, but the hypercalcemia did not improve. Histopathology of three resected parathyroid glands revealed hyperplasia and hypertrophy of the principal cells. After surgery, the fractional excretion of calcium examined in a spot urine sample was close to that in healthy dogs, but lower than that in a dog with primary hyperparathyroidism. Autoantibodies against calcium-sensing receptor (CaSR) were confirmed by incubating a cell line expressing canine CaSR with a serum sample from the hypercalcemic dog. Our report is the first to describe the diagnosis of acquired hypocalciuric hypercalcemia in a dog.