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20150924_1503271531-e1493401997820-169x300This horse has muscle atrophy.  The cause can be one of any number of three letter acronyms.  Acronyms for equine neurological diseases can be very confusing.  You probably understand EPM and PNE--equine protozoal myeloencephalitis and polyneuritis equi. Have you heard of EDM and EMD--equine degenerative myeloencephalopathy and equine motor neuron disease?  What are their causes and what are the signs your horse may have when afflicted with one of these mysterious conditions?  And of paramount importance-can they be treated?

We  provided exhaustive reviews of EPM and our guide to understanding polyneuritis equi.  If you missed them you can catch up at  Just search for Siobhan Ellison and the available books pop up.

The cause of equine degenerative myeloencephalopathy remains a mystery.  EDM damages multiple areas of the spinal cord resulting in muscle and locomotion disorders. Quite some time ago, EDM was the second most common diagnosis of spinal cord disease at Cornell University. There are a few folks that believe EDM has a genetic basis. In young horses EDM and EMD can occur together. The signs occur early on and will stabilize (not continue to get worse) when the horse is 4 or so, but signs won’t improve either. Another disease that is recognized in young horses is Wobblers, or cervical vertebral malformation, CVM.  The neuromuscular disease and an uncoordinated gait in CVM is due to physical restriction of the spinal cord in the spinal canal. CVM is recognized when young horses are started under saddle, although the condition was  present before that. As the horse grows and matures CVM gets worse. The important point is that these conditions are recognized in young horses.

Equine motor neuron disease is also a degenerative disease of the spinal cord.  EMD affects multiple areas of the nervous system.  Most signs in the horse are based on muscle weakness and loss of innervation to the muscles used in locomotion. Perhaps the stiff gait and low head carriage help differentiate EMD from EPM, EDM, CVM, and PNE. Remember Lyme disease (Borreliosis) also produces a stiff-gaited horse. The vector for Lyme disease is a tick and the disease is found more commonly in the Eastern US. EMD is induced experimentally by feeding a diet deficient in Vitamin E for a little over 3 years. Treating EMD with natural Vitamin E in the early stages can improve the outcome of the disease.  Grazing on good quality pasture is the best natural source of vitamin E for horses.

Based on what is known, Vitamin E supplementation can help with early onset EMD, but don’t expect vitamin E to help with EDM. Perhaps you can remember which one is treatable…EMD is “E to Medicate” and EDM is “E doesn’t Medicate”.  These are mnemonics that work for me. Sadly, some horses can develop more than one of these conditions at the same time. When horses have multiple diseases it will take a planned approach to rule in or rule out the cause of the signs. The first step is listing the clinical signs. Testing is an important part of ferreting out a diagnosis. Testing can include serum analysis for Vitamin E, muscle biopsy, and additional serum tests for infectious disease like protozoa or Borrelia.  Medicating and watching for a change in signs often leads to an expensive misdiagnosis.  Here is a comparative list of signs that can be observed in horses with EPM, EMD, and EDM. Your veterinarian can help you determine the proper approach to obtain a diagnosis and select an appropriate therapy.

Shifts weight on rear legs X
Difficulty standing X X X
Lays down a lot X
Muscle fasciculations/trembling X X X
Stiff gait X X X
Low head carriage X
Muscle atrophy X X X X
Weight loss X X X
Ataxia-symmetric X X X
Wide based stance X X X
Proprioceptive deficits X X X X
Diagnosed by post-mortem exam X X X
Weakness X X X X
Abnormal behavior X X X
Lameness X
Difficulty swallowing X X
Seizures X