Hypercalcemia and high serum parathyroid hormone-related protein concentration in a horse with multiple myeloma

In horses, absolute hypercalcemia is a rare condition that has been associated with renal disease, vitamin D toxicosis, hyperparathyroidism, and malignancy. Quantification of serum parathyroid hormone, ionized calcium, and parathyroid hormone-related protein (PTHrP) concentrations is useful in differentiating the causes of hypercalcemia. Concurrent demonstration of high serum PTHrP concentration and hyperglobulinemia in a horse with hypercalcemia should lead to a suspicion of multiple myeloma. If serum protein electrophoresis cannot definitively identify a paraprotein, quantification of specific immunoglobulin classes by radial immunodiffusion may be useful in confirming a diagnosis of multiple myeloma.