In this disorder, the part of the brain called the pars intermedia, a part of the pituitary gland, gets enlarged and overactive. As a result, the horse over-produces the stress hormones (non-sexual steroids, or cortisols) that are normally present at low levels in the horse. This overproduction makes the body feel "stressed out" all the time, prevents normal response to stress, and can cause many health problems such as:
- Immunosuppression - reduced ability to fight off infection
- Liver damage
- Hirsutism - retained or altered hair coat (this is a later sign, often only occuring after the patient has been overproducing cortisol for several years)
- Weight loss or gain
- Muscle loss, especially lack of muscle apparent on the topline and an enlarged, weak abdominal wall (sagging or large belly)
- Change in distribution of body fat
- Increased risk of poor blood sugar regulation
- Increased risk of laminitis / founder
- Personality change - becoming more calm or, rarely, crankier
Testing involves blood samples and sometimes stimulating the animal by giving a cortisol-type medication and then taking samples to see whether the animal's natural production can turn down rather than persist at an overly-high level. Due to natural variations in the levels of cortisol in the horse during the fall and winter as well as during times of stress, your horse may need to be tested during the spring or summer and when he isn't in a lot of pain or under stress.
There is an FDA approved medication, Prascend, to treat this disorder. Pergolide, the active ingredient, has been used for years. It is given once or twice daily for life and suppresses the overproduction of cortisol.
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