Pheochromocytoma in two horses.

A 12-year-old Standard-bred mare and a 21-year-old Quarter Horse gelding were treated for signs of abdominal pain and sweating. The mare also had muscle fasciculations, azotemia, and ataxia, and was euthanatized after signs of pain became refractory to analgesics. The gelding died when ventricular tachycardia developed during general anesthesia for exploratory celiotomy. Adrenal pheochromocytomas (bilateral in the mare), associated with retroperitoneal and intra-abdominal hemorrhage, were found on postmortem examination. Pheochromocytoma should be considered in older horses with signs of abdominal pain and sweating. Further consideration of pheochromocytoma should be afforded in older horses in which muscle fasciculations, ataxia, azotemia, and intraperitoneal hemorrhage are recognized. Identification, by per rectum palpation, of retroperitoneal swelling in the dorsal aspect of the abdomen also should alert the diagnostician to the possibility of a ruptured pheochromocytoma.