Signs and Treatment of Cushings Disease
Cushing’s disease occurs in various animals (e.g. dogs, horses, people), although the symptoms in horses are different than the symptoms in other animals (e.g. in dogs it results in hair loss whereas in horses it results in greater hair growth). When the disease occurs in horses, it is known as Equine Cushings Disease (or ECD).
ECD is the result of excessive steroid production by the adrenal glands. This is caused by the pituitary gland producing too much hormones and thus over-stimulating the adrenals, which is usually the result of either tumor growth on the pituitary or age-related growth of the pituitary gland itself. Both changes of the pituitary are age-related, so ECD is most common in older horses (over 15 years) but has been found in horses as young as seven.
The nature and cause of the disease itself was first explained by Harvey Cushing, an American brain surgeon, in’21. Consequently, the disease is named after him.
The symptoms of cushings disease vary somewhat from horse to horse, with the more common symptoms including: – Changes to the coat. It may become longer and curly. It may not be shed in Spring. In some cases the color becomes lighter. – Increased sweating. This is often due to the coat become longer and thicker, and retention of the winter coat into summer. – Weight loss despite increased appetite and food consumption. Changes to the body shape, with loss of muscle in back and neck, and development of pendulous abdomen. – General depression, loss of coat shine, horse looks ill. – Development of diabetes and a resulting increase in water consumption. This can be difficult to detect with pastured horses, but with stabled horses one may notice an abnormal amount of urine (or soiled bedding) in its box. – Development of laminitis. The most common cause of normal laminitis is carbohydrate overload due to eating spring grass, whereas ECD-caused laminitis is more frequent in autumn and winter since ECD is worse when the days are shorter (this is because the pineal gland is light-sensitive and as daylight decreases it stimulates the pituitary gland). – Immune system declines, leaving the horse more prone to infections and slower to heal from external injuries. – The depressions above the eyes fill in. These depressions are most evident when a horse is chewing, but gradually fill in with fat in ECD horses.
Any of these symptoms can be caused by a variety of illnesses other than ECD. Consequently, blood and urine tests are normally used to confirm that the cause is ECD (e.g. by measuring hormone levels and hormone response levels) and to rule out other possible diseases. Studies have shown that many horses with ECD are either not diagnosed or incorrectly diagnosed (the symptoms are incorrectly attributed to a different disease), with the result that they do not receive appropriate treatment.
Unfortunately it is not possible to cure ECD. However, one can slow the disease by the use of medication to reduce hormone production to normal levels. Note that some of these medications have strong side effects, so appropriate testing and control is required to prevent secondary illnesses (e.g. liver disease).
Since ECD and produce other illnesses, such as diabetes and laminitis, one needs to watch for symptoms of these related problems and treat promptly before they become serious.
One should also maintain the horse’s quality of life by treating any symptoms which make it uncomfortable. For example, if the heavier coat results in the horse becoming too warm, one should clip the coat in spring or summer.
Dr. Douglas Stewart is the author of Cushings Disease in Horses and owner of Horses for Sale
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