Cushing's Disease in horses

With advances constantly occurring in veterinary medicine we are taking better care of our animals and enabling them to live longer. We are also increasing our understanding of the diseases that affect our animals as they age. A common disease that affects many older horses is Equine Pituitary Pars Intermedia Dysfunction, or what is commonly known as Cushing’s disease. Cushing’s disease is one of the most commonly diagnosed endocrine disorders of horses. It is usually seen in older horses (15 years and older) but has been diagnosed in horses as young as 7 years. There seems to be no breed or sex predilection, but ponies appear to be more susceptible than horses.
Cushing’s disease is caused by an enlargement of the pituitary gland, which is located at the base of the brain and is responsible for producing hormones that control body functions. The enlargement or tumor causes an increased release of hormones, including ACTH, which then causes an increase in production of cortisol from the adrenal glands. Cortisol is a hormone that is secreted during times of stress, and it is this increase in cortisol in the body that causes the clinical signs seen with Cushing’s disease.

Symptoms of Cushing’s disease can vary and often become more obvious as the disease progresses. One of the most common clinical signs that owners notice is that their horse develops an abnormal hair coat. The hair coat changes can vary from persistence of long hairs on the head and belly, to incomplete shedding during the summer, to a long curly coat that lasts all year long. Other signs include drinking and urinating more, decreased energy, loss of muscle mass (loss of topline and a pot-belly appearance), laminitis, excessive sweating, delayed wound healing, and an increased incidence of infections such as foot abscesses, skin infections such as “rain scald”, or tooth infection. Horses with this disease often look “old”.

Occasionally Cushing’s disease can be diagnosed based on clinical signs alone. However there are a few diagnostic tests that can be helpful to make a diagnosis, especially if the signs are subtle. If you suspect Cushing’s, you should discuss with your veterinarian which test would be the best for your horse.

Unfortunately there is no cure for Cushing’s disease and treatment is aimed at controlling the release of ACTH from the pituitary gland and supportive care for the horse. Currently the medication of choice is pergolide. It is given daily and is a lifelong treatment for the horse. Improvement of clinical signs is usually seen in 1-2 months.

A very important part of caring for horses with Cushing’s disease is supportive care. This includes routine veterinary visits to check teeth and vaccinations, routine deworming and farrier appointments, clipping the hair in the summer, and prompt treatment of any infections. Often the diet needs to be modified as these horses do best on low-starch and low-sugar feeds such as grass hays and beet pulp, and avoiding grains and feeds high in molasses.

Another condition that is becoming recognized more frequently is Equine Metabolic Syndrome (EMS). In the past it was thought to be related to Cushing’s disease because in early stages the clinical signs can be similar, but new research has shown that it is a separate condition. Horses with EMS are typically considered to be “easy keepers” and are overweight with the majority of the fat deposited along the tail head, crest of the neck, shoulders and sheath. Often these horses have a problem with chronic laminitis and mares can be difficult to breed with abnormal heat cycles. The main problems in horses with EMS stems from insulin resistance similar to type II diabetes in people. These horses respond poorly to insulin so there is a build up of glucose in the blood which can lead to laminitis. EMS has been found in horses anywhere from 6-20 yrs of age and can be found in any breed. Blood tests will often show an increased level of glucose in the blood and fasting insulin levels will be high. If a dexamethasone suppression or ACTH test is performed to rule out Cushing’s disease, the results are normal. Management for EMS focuses on diet and exercise as there is no medical treatment available. Horses should be fed restricted calories with a diet high in fiber and low in sugars and carbohydrates, this means avoiding grains, molasses, and fresh grass. Just as in people, exercise will help decrease weight and aid in regulating glucose. If the horse is laminitic, then the laminitis should be treated before an exercise regime is begun.

Cushing’s is very common among older horses. Luckily if recognized early and treated, many horses do well and lead longer and healthier lives. If you suspect your horse has Cushing’s disease or EMS, contact your local veterinarian to ask their advice on the best way to diagnose and treat your horse.

Can you speak to Cushing's Disease in dogs?

Hi Pacamom,
Cushing's disease in dogs is somewhat similar to horses but in that is causes a release in the same hormones. Some of the classic signs include a pot belly appearance, thinning of the hair coat and increased drinking/urinating. I can give you a basic overview but Dr Jeff Danielson can probably give you a lot more information in the Pet Parks Forum!

Dr Shannon Harland

The most common clinical signs of Cushing’s Disease in dogs are increased appetite, increased water consumption/ increased urination, increased panting and a pendulous or pot-bellied abdomen. Cushings Disease or hyperadrenocorticism is most common in dogs greater than 6 years of age and is rarely seen in cats of any age.

There are two different types of hyperadrenocorticism in dogs- adrenal dependent, which indicates a tumor on the adrenal gland(s) or pituitary dependent hyperadrenocorticism, which indicates a hormone secreting tumor of the pituitary gland. Breeds over represented in the adrenal dependent group include dachshunds, german shepherds, Labrador retrievers, poodles and terriers. For the pituitary dependent cushing’s breeds more commonly seen are beagles, boxers, poodles, dachshunds, german shepherd dogs and terriers.

On physical examination dogs may have thin pigmented skin, bruising, muscle wasting, symmetric hair loss along the trunk and tail base and enlarged abdomen.

Let me know if folks would like additional information.

Jeff Danielson, DVM