Specific diagnosis in a horse with Cushing's disease and long-term therapy with pergolide

Objective: In this study diagnostic options of equine Cushings's disease and the follow up of long-term therapy with pergolide are discussed. Material and methods: A 13-year-old Quarter Horse mare was referred with conjunctivitis, sweating, polydipsia and polyuria. An analysis of blood (including ACTH concentration) and urine as well as the dexamethasone-suppression-test was performed. In addition a MRI examination of the pituitary gland took place. Pharmacokinetic parameters were determined after oral application of pergolide. Results: The mare showed neutrophilia, lymphopenia, hyperglycemia and glucosuria, The ACTH concentration was 138.6 pg/ml, Administration of dexamethasone resulted in a decreased suppression of plasma cortisol levels, A spherically increased pituitary gland could be shown by MRI The horse was successfully treated with 2 mu g pergolide/kg BW orally. The half-life time of pergolide was 6.8 hours. One year later the mare showed an increased general attitude with clinical estrus. Therefore the treatment was terminated. Two months later the horse developed hypercortisolemia with shock signs and died. The gross necropsy finding was an adenoma of the pituitary pars intermedia. Clinical relevance and conclusions: Dexamethason-suppression-test and evaluation of ACTH concentration are helpful methods for the diagnosis of equine Cushing's disease. The MRI was excellently suitable for imaging of the pituitary tumor, but cannot be administered in routine practice, The therapy with pergolide was effective. However, a long-term treatment can cause adverse effects. Splitting the single dose in two applications daily might reduce these reactions.