There have been advancements in the diagnosis and treatment of Cushing’s disease; however, previously there were no studies comparing the two most used medications—pergolide, a dopaminergic agonist, and cyproheptadine, a serotonin antagonist. Harold Schott II, DVM, PhD, presented “The Michigan Cushing’s Project” during the General Medicine session on Sunday afternoon.

In a study that ran from 1997 to 1999, Michigan State University and Michigan veterinarians followed 77 horses that had been confirmed to have Cushing’s disease based on the characteristic clinical signs and the results of either a low-dose dexamethasone suppression test (DST) or a thyrotropin-releasing hormone stimulation test (TRH). The horses were divided into three groups: a control (non-treated) group, those treated with pergolide, and those treated with cyproheptadine.

It was found that clinical improvement and a reversal of abnormal endocrine test results was better with pergolide than with cyproheptadine. In fact, treatment with cyproheptadine was found to be of little benefit when responses were compared with those observed in horses not receiving treatment. In addition, it was found that measurement of plasma adrenocorticotropin (ACTH) concentration alone is not a reliable endocrine test for diagnosis of Cushing’s disease, since both false positive and false negative results were obtained when compared to DST or TRH results for diagnosis.