Equine Cushing’s Disease By Brian S. Burks, DVM, Dipl. ABVP- Board Certified in Equine Practice Endocrine disorders have undergone much research in recent years. The most common endocrine diseases in the horse are pituitary pars media dysfunction (PPID, Cushing’s) and equine metabolic syndrome. The endocrine system comprises several organs to control body functions. These organs include the hypothalamus, pituitary gland, thyroid gland, the parathyroid glands, adrenal glands, pancreas, and reproductive organs (ovaries and testes). Endocrine diseases do not occur in horses as frequently as in other species; hypothyroidism, hyperthyroidism, and diabetes insipidus are rare in the horse. Pituitary pars media dysfunction (PPID) is the most common endocrine disorder of the horse. This is more accurate, as the affected portion of the pituitary gland is different in humans and canids. Thus, the term ‘Cushing’s’ is misleading, as it describes a specific human disorder of the pituitary gland. The pituitary gland receives input from the hypothalamus via dopamine, which inhibits the pituitary from making many different hormones. In the abnormal gland, the hormones are overproduced due to the lack of dopamine. The intermediate lobe of the pituitary gland becomes hyperplastic- the cells become bigger and make more products of a precursor hormone called Pro-Opio-Melano-Cortin (POMC) which then makes excessive ACTH, MSH, and others. The ACTH causes overproduction of cortisol by the adrenal glands, leading to a list of clinical signs. • Hirsutism- long hair that fails to shed completely • Chronic infections • Laminitis (founder) which is often repetitive and may have hoof abscesses • Excessive sweating • Increased water intake and urination – polyuria/polydipsia (PU/PD) • Lethargy • Loss of muscle mass- pot-bellied appearance • Infertility • Abnormal mammary gland development There are a number of diagnostic tests available for PPID, including ACTH testing and overnight Dexamethasone Suppression Testing. These are the standard tests, but others can be used if these are negative, but the horse’s appearance is suggestive of PPID. In addition to specific diagnostics, routine CBC and chemistry profiles can be helpful to identify infection/inflammation and other organ involvement. Blood glucose levels may be elevated in some horses. Treatment of PPID begins with management, though there are medications that can be used as well. It is important to be sure that the horse gets adequate nutrition with a low carbohydrate level. There are many low carbohydrate feeds available. They may also need additional protein, as cortisol breaks down the protein in muscle. Some horses that are very sensitive to carbohydrates may even need hay that is tested low in sugars. Grazing may need to limited by keeping them off of pasture or by using a grazing muzzle. It is also important to maintain vaccination, deworming, dental, and hoof care. Routine dental care can help identify dental caries, periodontal disease, loose teeth, and oral tumors. Routine steps for husbandry also include frequent bedding changes to minimize wet stalls which can lead to thrush and loss of viable hoof, body clipping as needed, frequent bathing if there is excessive sweating, and consistent monitoring for signs of infection. Laminitis is the worst clinical sign and can be devastating. Hoof changes and pain develop insidiously. It is related to the excessive cortisol levels and its anti-glucose effects. The exact pathway to cause laminitis has not been fully elucidated. These horses may need special shoeing and frequent trimming. They may also need pain control with medications such as phenylbutazone, flunixin meglumine, or firocoxib. Horses further along in the course of disease may benefit from daily administration of pergolide. It can provide substantial relief from clinical signs. Prascend is the FDA approved form of pergolide. Sometimes cyproheptadine can be added to the pergolide dose, but it is rarely efficacious as a sole therapy. Herbal supplements have anecdotally been reported to improve clinical signs, but this has been shown scientifically to be of no value when compared side by side with pergolide. It should also be noted that many supplements do not contain the active ingredients listed on the packaging, and that there is no standardization for purity and quantity, making it impossible to know what is being purchased. In conclusion, PPID is a disease of (older) equids that can be managed, but not cured. Chronic infections and laminitis are frequent clinical manifestations and can be difficult to control in some horses. Thus, early recognition and veterinary intervention, along with farrier care are imperative to help the horse maintain a good quality of life. Fox Run Equine Center foxrunequine
Posted on: Tue, 30 Dec 2014 14:00:00 +0000
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