Disease Du Jour: Equine Degenerative Myeloencephalopathy (EDM)

Dr. Emilie Setlakwe discusses a new type of equine degenerative myeloencephalopthy (EDM).
bucking horse from back
Horses with the new type of EDM are generally older and have behavior changes.

Most veterinarians have heard about equine degenerative myeloencephalopathy (EDM). However, Emilie Setlakwe, DVM, DACVIM, MS, clues her fellow practitioners into what might be a previously unrecognized form of EDM in this episode of the podcast. “I feel like this is a lot of what I do any more,” she said of diagnosing this new EDM in horses.

Typically, EDM is a disease of young horses of specific breeds that is characterized by development of symmetric ataxia. Researcher noted that vitamin E deficiency and a hereditary predisposition were considered the most significant factors in the pathogenesis of this disease. Another name for this disease is Equine neuroaxonal dystrophy (eNAD), and Setlakwe said the terms sometimes are used interchangeably.

“The type of EDM I talk about is different,” said Setlakwe. “For the last 10 years, there has been a resurgence of this disease. But it is different from the one in young horses with low vitamin E levels. These horses have cerebral signs.”

What else stands out is that the horses with the newer form of EDM that Setlakwe are generally older (from 5-15 years old), warmbloods, mostly European imports, and they have behavior changes that are different from those seen in the typical young horse with EDM.

Setlakwe posed: “Is it the same disease? A different disease? Delayed onset due to genetics? Cases that are missed when they are younger?”

Diagnosis of This Type of EDM

Setlakwe said veterinarians don’t have a good way to diagnose this disease, and it can be challenging. “Often it’s from exclusion,” she said.

There is no antemortem diagnosis available. There was a biomarker test that was available commercially, but the test is not used any more because of low sensitivity, said Setlakwe.

She recommended doing a thorough history and physical exam, including a neurologic exam. She said you might find subtle ataxia of grade 1 or 2, or you might not. “There will be some sensory abnormalities of the head and neck,” she noted. She said the menace response will be affected in horses that have this type of EDM.

Setlakwe said veterinarians should pay attention to owners’ remarks in the history. The horse might have unpredictable, erratic and sometimes dangerous behavior that gets worse over time. The horse might seem to be “not happy” any more. It might only travel normally in one direction, and the other direction stop (i.e., jumping or over ground poles). Owners have said they don’t “recognize” the horse and the horse doesn’t “recognize” the owner. They say the horse isn’t the same animal as it was before.

“I believe this is true,” said Setlakwe. “The architecture of the brain and spinal cord has changed. Listen to the owners suggestion that there is a personality change.”

Some owners think the horse has visual issues, but vision exams seem normal. Setlakwe said this might be due to signals from the eyes not making it to the brain due to the disease.

“Once you do your neurologic exam, look for ataxia in all four limbs,” recommended Setlakwe.

She said you might or might not see changes on X ray, and myelograms can be normal in affected horses. Spinal fluid cytology can be normal, as can vitamin E levels.

She said in one horse that the contrast column was large versus the diameter of the spinal cord. She said other practitioners also have noticed that on X ray and in necropsy.

Setlakwe said many of these horses go through a lot before they are diagnosed or become too dangerous to ride. They have trainer changes, bit changes, injections, saddle fit…”usually it is a year down the road before I see them,” said Setlakwe.

She said veterinarians who treat these types of horses need to be on the lookout for this disease. “Don’t condemn them until the horse has gone through the diagnostic process,” she stated.

However, over time these horses deteriorate. Some faster than others.

She recommended that veterinarians with patients that fit this description of this newer form of EDM have a necropsy done to confirm the changes in the spinal cord. Then share that diagnosis with owners.

“Owners are relieved with the necropsy diagnosis,” said Setlakwe.

Editor’s note: Check out this article AAEP 2021: EDM Causes Poor Performance in Horses.

About Dr. Emilie Setlakwe

Emilie Setlakwe, DVM, DACVIM, MS, joined the team at Tryon Equine Hospital in North Carolina in August of 2015. She had completed a 3-year internal medicine residency at the University of Pennsylvania’s New Bolton Center. Prior to that, she worked at a large animal internship in medicine and surgery at the University of Guelph and obtained a Masters degree form the University of Montreal in respiratory diseases of horses.

Setlakwe’s areas of interest include equine respiratory diseases, neurology, evaluation of poor performance, gastroenterology, neonatology and critical care. She has a passion for veterinary humanitarian work and has traveled to Nicaragua, where she provided veterinary care to working equids. Setlakwe also enjoys working on a variety of species, some of which include pet small ruminants (sheep and goats), camelids and pigs. In her spare time, Setlakwe enjoys riding her horses and competing in three-day events and dressage. She also enjoys spending time with her husband, Tim, and her son, Simon.

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