Pituitary pars intermedia dysfunction or Equine Cushings Disease

Pituitary pars intermedia dysfunction (PPID) in the horse is a slowly progressive disorder with characteristic clinical features. Also known as equine Cushing’s disease because of its similarity to Cushing’s disease in humans. Unlike humans, the condition in horses is caused by adenomas or adenomatous hypertrophy of the intermediate lobe of the pituitary gland located in the brain.

The clinical signs include hirsutism (excessively long hair), hyperhydrosis (increased sweating), increased water intake and urination, muscle wasting, susceptibility to bacterial and parasitic infections, lethargy, bulging eyes and laminitis. Laminitis is generally the most serious clinical sign.

PPID is caused by functional hyperplasia of the intermediate lobe of the pituitary gland. This enlargement apparently occurs because of an age related decline in the neurotransmitter dopamine, which has an inhibitory affect on the intermediate lobe of the pituitary gland. The specific reason(s) for the high incidence of laminitis in horses with PPID is unknown. They may be partially related to a deficiency in circadian fluxuations of corticosteroid secretion. This has potential adverse affects on the vascular integrity in the hoof and structural stability of the hoof's lamellar connective tissue.

The diagnosis of PPID is made by consideration of the clinical signs, age of the horse, and laboratory testing. There are numerous laboratory tests including measurement of adrenocorticotrophic hormone (ACTH) and/or the dexamethasone suppression test.

Currently the one treatment available which has shown clinical improvement for Cushings Disease is a drug called Pergolide. The drug replaces dopamine, so it is generally given for life. Sometimes this drug can be used in conjunction with another drug called Ciproheptidine. While these drugs can provide effective management of the disease, they do not appear to be a permanent cure.

For more information:

http://findarticles.com/p/articles/mi_m0FDN/is_2001_Sept/ai_80532257/pg_1?tag=artBody;col1

http://www.infovets.com/healthyhorseinfo/E136.htm

http://www.aaep.org/ask_the_vet_questions.php?category_id=79