Cushing’s Disease and your Horse
An EquestrianMag Exclusive Article

Cushing's disease, a dangerous illness best known for afflicting dogs, is also a threat to horses, and their owners need to be on the lookout for its systems.

According to publisher and horse owner Shelly Mellot, Cushing's Disease (scientifically known as Hyperadrenalcorticism) is a disease that hits horses and canines. “It’s caused by excessive levels of gluocorticoid (a type of steroid made by the pituitary gland),” Mellot said. “You have to take the disease very seriously because it can lead to other problems.”

While potentially deadly, this troubling disorder fortunately offers several obvious symptoms that horse owners can spot in time to provide effective treatment. These signs include:

• Chronic urinary tract infections
• Darkening of the skin
• Deterioration of muscle tissue
• Difficulty Breathing
• Distended abdomen
• Hair loss over the body
• Increased thirst
• Shrinking of the testicles in males
• Thinning skin

Causes include pituitary gland tumors, adrenal gland tumors and the chronic additions of naturally occurring, but excessively produced steroids. About 85% of all cases are due to tumors of the pituitary gland at the base of the brain.

“Our horses can develop a form of diabetes that’s resistant to insulin,” Mellot added. “The horses may be weak and sleep most of the time. They may develop seizures or other nervous system changes.”

If an owner suspects that his or her horse has this illness, there are common lab tests to diagnose it – including cholesterol tests, blood glucose panels and urinalysis. X-rays and CT scanning can also spot pituitary tumors. Often the disease is diagnosed by clinical signs and a procedure called gland function testing.

Drug testing and analysis of the horse’s cortisol level will be the deciding factor on how severe the disease is. However, treatment usually consists of destroying the part of the adrenal cortex that produces the excessive steroids.

For concerned horse owners looking for the best treatment, the drug Mitotane (or Lysodren) is used as the primary answer to the disease’s effects. An initial dose period is followed by a maintenance dose period – and the horse’s owner can administer the drug without a vet’s assistance.

Although standard protocols and doses are used, it is impossible to predict what dose of Lysodren will work for an individual horse. Owners give the medication daily until symptoms improve. The most common sign used is a decrease in water consumption. Then a maintenance phase is developed that uses a dosage once or twice weekly.

Throughout treatment (especially during the five to 14 day induction phase) owners need to closely watch their horses for listlessness, loss of appetite, vomiting and diarrhea - indications that cortisol levels have fallen too low. If an owner notices these signs, he or she must give the horse cortisone. Your vet can help you with that.

Periodic laboratory tests and Lysodren dosage adjustments will probably be made during the lifelong treatment of Cushing’s Disease. About 50% of horses treated for the pituitary form of Cushing’s will relapse at some point, and about 33% experience a reaction to Lysodren.

Cushing’s disease is complex and may be difficult to figure out at first. However, most owners discover that treating and monitoring their horse becomes second nature. The animal will have to be monitored lifelong.

The average life span of a Cushing patient after diagnosis is about 2 years. Complications include blood clots, infections, high blood pressure, heart failure, inability to control the disease and increased nervous signs.

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