Treatment of Cushing's Syndrome in the Dog with an Adrenocorticolytic Agent (o,p′DDD)

Abstract

SUMMARY An adrenocorticolytic agent (o,p′DDD) was given orally to treat 18 dogs with Cushing's syndrome over a period of 3 years. Diagnosis was based on clinical, laboratory, and endocrinologic findings. Although plasma corticosteroid values (utilizing a competitive protein-binding radioassay procedure) were of only limited value in differentiating dogs with Cushing's syndrome from either normal dogs or dogs with other disease conditions, differentiation based on plasma corticosteroid values after stimulation with adrenocorticotropin ( acth ) proved to be of great value. Response to o,p′DDD therapy was excellent in 13 dogs, 9 of which are presently alive, with complete remission of clinical signs; the 1st dog treated with o,p′DDD is still alive and well 3 years later. Of 2 dosage schedules evaluated, an initial daily dosage schedule of 4 to 13 days followed by a once weekly dose of o,p′DDD resulted in the longest remission periods; none of the dogs thus treated has relapsed. The only side effects that could be directly related to the use of o,p′DDD were depression and anorexia in a few dogs. These effects were completely reversible on discontinuance of treatment. None of the dogs treated has ever developed clinical or laboratory evidence of adrenal insufficiency, despite the development of low plasma corticosteroid concentrations in most of them. Serious hepatic toxicosis due to o,p′DDD therapy could not be detected by either serum glutamic pyruvic transaminase ( sgpt ) or bromsulphalein ( bsp ) tests. Necropsies were performed on all dogs that died; specific cytotoxic changes were found in the adrenal cortex only, and were most extensive in the zona reticularis and zona fasciculata, whereas damage to the zona glomerulosa was relatively mild. Changes attributable to treatment with o,p′DDD could not be found in other tissues.