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Equine Cushing’s Disease

What is Equine Cushings Disease? Equine Cushings Disease (ECD) also known as Pituitary Pars Intermedia Dysfunction (PPID) is caused by dysfunction of the pars intermedia of the pituitary gland. The pituitary gland is a small gland in the brain that is responsible for controlling many metabolic functions in the body. Normally, the pituitary gland signals the adrenal glands (tiny glands located by the kidneys) to produce adequate amounts of cortisol (a natural version of steroids such as prednisone and dexamethasone - these are not to be confused with the steroids used by athletes). With ECD, however excessive amounts of cortisol are produced, which results in a myriad of possible clinical signs.

Signs of ECD: ECD usually occurs in horses over 15 years of age. Signs can include all or only one of the following:

  • Excessive and/or curly haircoat (known as hirsuitism)
  • Excessive drinking and urination
  • Immunosuppression or recurrent infections
  • Chronic laminitis
  • Change in body condition – loss of condition despite good appetite, muscle wasting

ECD diagnosis: A diagnosis can sometimes be made on the basis of history and physical exam findings alone. However, it is more definitive to use one of the following blood tests along with history and clinical findings to make a definitive diagnosis:

  • Dexamethasone Suppression Test – A blood sample is taken in the afternoon on day 1. At the same time an intramuscular injection of dexamethasone is given. A second blood sample is taken approximately 19 hours later. Cortisol levels are measured in both samples. In a normal horse, the cortisol levels in the second blood sample should be lower than the first. In a horse with ECD however, the second sample may be the same or even higher than the first because the pituitary gland does not react appropriately.
  • Baseline ACTH levels – ACTH levels are usually increased in horses with ECD. It is necessary to handle blood samples in a very specific manner in order to assure accurate measurement back at the laboratory. Insulin and glucose are generally measured at the same time as ACTH.

Despite our best efforts, there are patients that elude diagnosis. This is frustrating for the owner and the veterinarian. Regardless of test results, our veterinarians at OSEA are trained to guide you through the process.

Treatment of ECD: Unfortunately there is no cure for ECD. Rather, treatment includes a multifaceted approach using medications to regulate pituitary gland function, nutrition and other supportive measures.
Currently, Pergolide Mesylate is the drug of choice for treating ECD. The only FDA approved medication labeled for treatment of ECD is called Prascend. It is a small tablet given orally every day for the rest of your horse’s life. Because Prascend is FDA approved, it has guaranteed saftety, efficacy, ease of dosing and a much longer shelf life than compounded versions of Pergolide.  ACTH levels in the blood are used to monitor the pergolide dosage. ACTH levels should be checked one month after any change in dose or every 6 months in a stable patient.

There are many alternative therapeutic compounds available on the market for treatment of ECD. Many of these products carry extremely positive testimonials and claims of beneficial outcomes. Unfortunately, unbiased scientific studies are lacking to substantiate these claims. 

Horses with ECD should be fed a relatively low-starch diet due to the increased risk of laminitis. For more specific nutritional information, see Feeding the Metabolic Horse.  

Diligent hoof care is also imperative to reduce the risk of laminitis or to help treat already established laminitis. Because horses with ECD are more susceptible to infection, it is even more important to keep their vaccinations up to date, deworm regularly and identify signs of illness as soon as possible. If an excessive hair coat is part of your horse’s ECD then it is necessary to clip the hair coat during the warmer months of the year to keep him from overheating.