Idiopathic hypercalcemia in cats

Unexplained hypercalcemia has been increasingly recognized in cats since 19 90. In some instances, hypercalcemia has been associated with calcium oxala te urolithiasis, and some affected cats have been fed acidifying diets. We studied the laboratory findings, clinical course, and treatment of 20 cats with idiopathic hypercalcemia. Eight (40%) of the cats were longhaired and all 14 cats for which adequate dietary history was available had been fed a cidifying diets. Clinical signs included vomiting (6 cats), weight loss (4 cats), dysuria (4 cats), anorexia (3 cars), and inappropriate urinations (3 cats). Hypercalcemia was mild to moderate in severity, and serum parathyro id hormone concentrations were normal or low. Serum concentrations of phosp horus, parathyroid hormone-related peptide, 25-hydroxycholecalciferol, and calcitriol were within the reference range in most cats. Diseases commonly associated with hypercalcemia (eg, neoplasia, primary hyperparathyroidism) were nor identified despite thorough medical evaluations and long-term clin ical follow-up. Azotemia either did not develop (10 cats) or developed afte r the onset of hypercalcemia (3 cats), suggesting that renal failure was no t the cause of hypercalcemia in affected cats. Seven of 20 cats (35%) had u rolithiasis, and in 2 cats uroliths were composed of calcium oxalate. Subto tal parathyroidectomy in 2 cats and dietary modification in 11 cats did not result in resolution of hypercalcemia. Treatment with prednisone resulted in complete resolution of hypercalcemia in 4 cats.