MITOTANE (O,P'-DDD) RESISTANCE IN A DOG WITH PITUITARY-DEPENDENT HYPERADRENOCORTICISM AND PHEOCHROMOCYTOMA

A dog was presented with a 2 year history of polyuria and polydipsia d ue to pituitary-dependent hyperadrenocorticism. A low-dose dexamethaso ne suppression test and measurement of plasma ACTH concentration confi rmed the diagnosis. Treatment was instituted with mitotane at 44 mg/kg /day and then 88 mg/kg/d without complete resolution of signs. The dog collapsed with signs consistent with liver disease and was euthanased . Necropsy revealed a phaeochromocytoma of the left adrenal medulla wi th extensive metastases to the liver. A chromophobe adenoma of the par s intermedia of the pituitary was found.