Cushing’s Disease
November 16, 2009
Learn to spot symptoms of early Cushing’s disease.
Question:
I have an 18-year-old gelding that is considered obese. I went out to feed, and he was all sweaty. I know he hadn’t been running or my other gelding would have been hot, too. He had no fever. I checked him hourly and got him cooled off. He is very fuzzy from his winter coat, and he always sheds out just fine. It’s not curly hair, either. I only feed him grass hay (brome/crested wheatgrass), and he has a 20-percent lick-tub, so there is no grain. Any idea if something is wrong?
Thanks, Yvonne Rocens
Answer:
Daily turned to our friend and Journal horse health columnist Dr. Tom Lenz for help.
Yvonne,
It is very difficult to determine what’s wrong with the horse without seeing it, but it sounds like an early Cushing’s disease horse who may have a slow-growing pituitary tumor. These horses are always very fat, middle to old age and have long hair. When the condition first occurs, they will shed out normally. But over the years, they will reach the point where they do not shed out. Unexpected sweating is often seen.
I recommend that you have your veterinarian examine the horse, as there are diagnostic tests that can be run and drugs (pergolide) that can be administered to treat it. These horses are also prone to foundering.
More on Cushing’s Disease
Dr. Lenz recently wrote a column on pituitary gland tumors:
Many equine veterinarians believe they are seeing an increase in the incidence of a condition known as hypophysial adenoma (pituitary gland tumor), which produces dramatic clinical signs in affected horses. The pituitary gland is located at the base of the horse’s brain and is responsible for controlling a number of body functions. Hypophysial adenomas are most often diagnosed in middle aged to older horses of either sex. The minimum age reported has been 7 years, but the average age is around 20.
Usually the first thing owners notice when their horse has a pituitary tumor is that the horse fails to shed its hair in the spring. Affected horses develop an excessively long, shaggy hair coat that is often curly or matted. About 60 percent of horses with pituitary tumors sweat excessively and over 30 percent of them develop secondary diabetes (Cushing’s disease). The diabetic horses will drink massive quantities of water and will urinate frequently, making it difficult to keep their stall dry. The horses’ feet grow too long and too rapidly, just like the hair coat, and 25 percent of the affected horses experience unexplained bouts of laminitis (founder). The horses may experience repeated infections. Their skin is often scaly or greasy and susceptible to secondary skin infections. Despite the fact that the horse’s hair coat continues to grow and does not shed, the mane and tail remain normal. As the tumor enlarges, the horse may become swaybacked and develop a “potbellied” appearance. Many of the horses have unusual deposits of fat behind the eyes, which cause them to bulge slightly.
Pituitary tumors are diagnosed on clinical signs as well as the results of blood and urine tests. Because the signs exhibited by horses suffering from pituitary tumors are varied and may mimic a number of other diseases, a veterinarian should be called upon to give the horse a thorough examination. The horse’s cortisol and blood glucose levels are helpful in confirming the existence of the tumor. Thyroid-releasing hormone response and dexamethasone suppression tests are also helpful in diagnosing the condition.
Treatment of horses with pituitary tumors varies with the severity of the clinical signs, the age of the horse, and secondary complications, such as diabetes. Some horses and ponies appear to do well for years despite the presence of a tumor and merely require frequent body hair clipping and access to sufficient amounts of water. Recurrent infections require treatment, and some affected horses need to be fed increasing amount of feed to offset their weight loss. Insulin does not seem to work in affected horses because the diabetes is secondary to the tumor. There are a number of drugs (primarily cyproheptadine and pergolide) used in people and dogs to treat similar conditions that may benefit some horses. Neither of these drugs are approved for use in horses. There has been limited published data on the therapeutic efficacy of these drugs. However, a number of equine internal medicine specialists believe they demonstrate promise in controlling tumor growth. Unfortunately, long-term drug therapy appears to only control tumor growth, not cure the condition.
If you have a middle-aged to older horse that is exhibiting clinical signs suggestive of a pituitary tumor, especially a long, shaggy hair coat that does not shed, call a veterinarian. The sooner a diagnosis is made, the sooner a treatment plan can be outlined and initiated.
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