Q. About a year and a half ago, my horse was diagnosed with EPM (equine protozoal myeloencephalitis), which he was treated for, and I haven't seen any signs since. Now he's having hock issues. My veterinarian injected him with pure acid (he didn't use steroids in fear of an EPM relapse). There was excess discolored fluid in all of the joints, and one was very bloody. Because they were so bad, my veterinarian came back six weeks later and injected them again. I'm desperate for a healthy, rideable horse.

Ann, via e-mail

A. Because there is no definitive pre-mortem diagnosis for EPM, you might find significantly differing opinions from veterinarians. For gait problems, the ability to distinguish between neurological problems due to EPM and lameness can be very difficult. The likelihood of identifying the problem accurately is subjective and at least in part dependent on the experience of the examiner's experience with neurological problems and lameness issues. I recommend you seek more than one qualified opinion. A consensus might be more likely to be accurate. In my part of the world, I believe that EPM is overdiagnosed, primarily because of the number of normal horses that test positive in both the blood and the spinal fluid.

Having said that, it is still possible that your horse has neurological impairment from other problems, such as neck arthritis instability. If you are still interested in pursuing this, I would recommend you have a specialist examine your horse and determine 1) if your horse is neurologic or if it is lame, 2) where the neurologic problem or the lameness is specifically coming from, and only then 3) what might be causing it.

If you do wind up treating for EPM again, I would recommend considering some of the newer medications available (e.g., Marquis or Navigator) if you have not already used them.

If your horse fails to respond to one of these 30-day therapies, it is important to consider that a different neurological disease or a lameness might explain why the therapy failed. The interpretation of the color and character of joint fluid that you have seen with the joint injections is, in my hands, an unreliable way to determine if a joint problem exists. Most, if not all, sport/performance horses develop hock problems as they age. The need to inject the hocks is not surprising to me at all. I personally have no problem putting steroids in the hocks, even in EPM suspects. I do not believe that steroids really affect the likelihood of relapse of EPM, nor do I believe that the drug levels that would be obtained after injecting the hocks would be anywhere near high enough or long enough to affect the EPM that the horse might or might not have.

In my experience, lameness affecting the pelvis, sacroiliac, and lumbosacral regions might look very much like a neurological problem. The evaluator for these conditions needs to be experienced in dealing with these problems.

About the Author

Bradford G. Bentz, VMD, MS, Dipl. ACVIM, ABVP (equine)

Brad Bentz, VMD, Dipl. ACVIM, ABVP, ACVECC, owns Bluegrass Equine Performance and Internal Medicine in Lexington, Ky., where he specializes in advanced internal medicine and critical care focused on helping equine patients recuperate at home. He’s authored numerous books, articles, and papers about horse health and currently serves as commission veterinarian for the Kentucky State Racing Commission.

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