Equine Cushing's disease often confused with EMS

By Marty Metzger
Correspondent

Equine Cushing's disease and equine metabolic syndrome share many symptoms, thereby causing confusion in diagnosis. In fact, veterinary research conducted prior to 2004 often contains erroneous information responsible for misdiagnosis.

Gabrielle Landolt, DVM, is assistant professor in equine medicine at Colorado State University and a recognized authority on both diseases.

"Diagnostic techniques are getting better, and people are becoming quite aware, so it is being diagnosed earlier," Landolt commented on equine Cushing's. "Therefore, it's now being recognized more than before in younger horses."

Diagnosis is accomplished through blood tests measuring hormone levels. According to Landolt, the better ones are the dexamethasone suppression test and domperidon test. These can be done by any vet via multiple blood samples.

The clinical signs common to equine Cushing's include a long, shaggy coat (hirsutism) and delayed or abnormal shedding; excessive drinking and urination (polydipsia/polyuria); excessive sweating; muscle loss with possible muscle weakness; lethargy; chronic/recurrent laminitis; chronic infections or slow wound healing.

Active research for the disease's underlying cause is being conducted in many laboratories, especially at the University of Tennessee, University of Louisiana and Michigan State University. These institutions are also seeking an even better diagnostic test.

It is generally accepted that equine Cushing's is caused by a benign growth (adenoma) on the pars intermedia of the anterior pituitary gland. The compromised gland secretes excessive cortisol and other hormones, producing the clinical symptoms noted above, Landolt said.

One debilitating condition seen in Cushing's-affected horses is laminitis. This can be chronic or recurrent, often as a result of grass founder, and believed to be secondary to hypercortisolism.

Glucorticosteroids suppress the immune system, thereby putting horses with Cushing's at a greater risk of sinus and respiratory tract infections, hoof and tooth abscesses, skin ailments and heavy parasite loads (causing excessive weight loss), Landolt noted.

Warding off secondary, concurrent problems best treats equine Cushing's, first described in 1932. Regular deworming, farrier and dental care, along with careful monitoring of other clinical symptoms, are critical in maintaining the afflicted animal's optimum health.

Several medical treatments are available. These include Peroglide, which is the most common, and Bromocriptine. Landolt said these two medications act directly on the pituitary gland. A less expensive drug is Cyproheptadine, which modulates rather than blocks secretion of the pituitary gland.

The confusion between Cushing's and EMS is due to overlapping symptoms. Although some horses can be accurately diagnosed through clinical signs alone, others must be tested for an accurate determination.

While Cushing's is reported in all breeds and types, EMS is most common in obese equines and "easy keepers," usually between ages 6 and 20, and in ponies, Morgans, Saddlebreds, Pasos, Spanish Mustangs and European Warmbloods. The types most often diagnosed exhibit large, weighty crests, swollen sheaths in geldings, and fat deposits in the gluteal region. Laminitis is common in many of these horses.

However, horses with EMS have normal pituitary glands, as noted in necropsies. EMS individuals don't exhibit elevated blood cortisol levels. Horses with many classic Cushing's symptoms that test negative for it often are ultimately diagnosed with EMS.

To best manage EMS, an obese horse's weight must be reduced and controlled, especially in cases of laminitis. Insulin sensitivity can be increased by use of supplements such as chromium, magnesium or vanadium.

Preventive measures that have met with some good success include feeding low-starch diets balanced with vitamins and minerals, especially in breeds and family lines predisposed to EMS and in inactive horses.

Horses in the wild don't eat massive amounts of grains. The common practice of feeding grain, especially in large amounts, to youngsters, performance horses, lactating mares and others, should be carefully reassessed.

Equine Cushing's disease and EMS can shorten horses' life spans due to secondary conditions. But, proper and early diagnosis, treatment and implementation of excellent wellness practices can help insure a better quality of life for these equines.