Pituitary pars intermedia dysfunction: equine Cushing's disease

Abstract

PPID in older equids has become a major health concern of horse owners. In response, equine practitioners have made greater efforts at understanding, diagnosing, and treating this disorder. Although PPID is recognized to be a different form of pituitary-dependent hyperadrenocorticism than is seen in canine or human patients, relatively little is known about the pathophysiology and natural progression of the disease. At present, the diagnosis is best supported by manifestation of characteristic clinical signs and endocrinologic test results, preferably a supportive DST result. Treatment must focus on improving overall health care, including body clipping, dentistry, and nutrition. As the condition progresses, administration of pergolide or a combination of pergolide and cyproheptadine is currently considered the best medical treatment. The time point at which medication should be added to improved health care and management changes is not currently known, but loss of body condition and development of hyperglycemia suggest more advanced PPID that would likely benefit from drug therapy. Whether medical treatment needs to be continuous or could be intermittent is also unknown. As the demand for treatment of affected equids continues to increase, clinical response and endocrinologic testing data as well as pharmacologic data for currently used drugs and other agents should be expected. Similarly, novel medical, and perhaps surgical, treatment strategies for this condition should also be anticipated in the future.