Equine Cushings Disease
Equine Cushings Disesase, or PPID (pituitary pars intermedia dysfunction) as it is known by veterinary scientists, is a disorder of the pituitary gland (located at the base of the brain) that results in hormonal imbalances, causing a variety of symptoms: long, possibly curly or wavy hair coat that does not shed normally; muscle wasting; increased sweating, water consumption and urination; abnormal fat deposits in the crest of the neck, tail head, above the eyes, and in the sheath area of stallions and geldings, immune system suppression with increased susceptibility to infection; laminitis; lethargy or poor performance; infertility and weight loss. The onset of these signs usually occurs when the horse is in its late teens or early twenties.
Cushings Disease develops when a specific part of the pituitary gland (pars intermedia) becomes enlarged and overactive, producing excessive amounts of the hormones POMC (pro-opiomelanocortin) and several of its derivatives, including ACTH(adrenocorticotropic hormone). In normal animals, the pituitary is regulated by dopamine secreting nerve cells in the hypothalamus (a nearby part of the brain that regulates basic body functions such as hunger, thirst, temperature and blood pressure). For reasons not yet fully understood, Cushings develops when the pituitary gland is no longer kept in check by the faulty hypothalamus. The increased levels of POMC and ACTH from the pituitary then act on the adrenal glands (located near each kidney) causing them to overproduce cortisol, the “stress hormone”. The increased circulating levels of all these hormones are responsible for the clinical signs of Cushings Disease.
Diagnosis of Cushings disease is accomplished by physical examination and laboratory testing. Several tests are available, and the exact protocols used varies among cases, but may involve testing levels of cortisol, ACTH, thyroid hormone, blood or urine glucose, insulin, as well as complete blood counts and serum biochemistry analysis.
Treatment of Cushings Disease consists of:
1. Management strategies to address of prevent complications from the disease
2. Specific medication to normalize pituitary gland function
It must be stressed that mangement is life-long as the disease process is irreversible. Dietary restriction of soluble carbohydrates is paramount, as affected horses are often insulin resistant and hyperglycemic. Sweet-feed and other high sugar foods should be replaced with diets emphasizing fiber and fat. Strict attention to hoof care is critical, especially in the case of laminitic horses. Early recognition, diagnosis, and aggressive treatment of infections, as well as routine dental care and vaccination and parasite control is of utmost importance, due to the immunosuppressive effects of increased cortisol levels. Supportive care such as body-clipping long hair coats, preventing exposure to extremes in weather conditions (fans, blanketing, etc.) and minimizing stress is recommended.
Specific drug therapy is aimed at reducing the amount POMC and ACTH secreted by the pituitary. The current drug of choice is pergolide, which mimics the dopaminergic effect of the hypothalamus on the pituitary gland. Other supplements such as chromium and magnesium may be beneficial at regulating glucose and insulin, and additional drugs and herbal therapies are currently under investigation.