Equine Motor Neuron Disease. An astute owner was aware that something was wrong..
I received a call from a worried horse owner one evening. Her 13 year old Paso Fino gelding, Bennie, had not been acting right the last few days and had recently lost weight. He was eating, drinking, passing normal manure and walking comfortably but when he got up after lying down his whole body would tremble. When he stood his legs were positioned camped under him, in the shape of a "V." She had already separated him from the other horses, none of whom were showing similar signs. I went out to see Bennie. In my head I was thinking, is this horse neurologic? in pain? virus? The weight loss and unusual stance triggered something in my mind from way back. Certain vitamin deficiency or excess, whether from lack of intake or the body's inability to process them, can effect muscle mass and tone. One vitamin deficiency, vitamin E can lead to horses standing in a "V" stance. Hmmm - thank you memory.
Physical exam was unremarkable and he walked better than he stood. His stance was exactly as she had described. He had lost between 50-75 pounds and his topline was less developed. He remained bright and alert the entire time I examined him. He was able to swallow and had good tail tone (not botulism), his cranial nerves were normal and he was very weak but not ataxic (less likely EPM but still on the ruleouts), never rule out Rabies, lead toxicosis, or storage myopathy? I needed more information to help with the diagnosis so I drew blood for CBC, Chemistry, vitamin E and selenium levels. Since I was most suspicious of Vitamin E deficiency I gave her some Vitamin E capsules and prescribed natural vitamin E, 7,000IU orally, daily.
Two days later I went to see how he was doing. The CBC and chemistry had returned, all normal. I had done some reading of papers about Equine Motor Neuron Disease and found the clinical signs of neuromuscular weakness result from the generalized denervation muscle atrophy. The pathogenesis of EMND is not fully understood but is thought to result from free radical damage. A chronic lack of antioxidants is implicated in the pathogenesis. Equine motor neuron disease occurs sporatically and affects horses of all ages and breeds. (Diver, TJ, Equine Vet J 26:409). A chronic vitamin E deficiency is thought to be the most important factor in the cause of the disease based on the fact that affected horses consistently have low plasma Vitamin E concentrations.
I administered DMSO, a potent free radical scavanger, in a liter of saline IV, and left instructionts to give him an antiinflammatory dose of steriods orally, daily for one week, as well as natural vitamin E.
At the end of the week the vitamin E and selenium results returned from the Michigan State lab, both were abnormally low. I researched a good selenium supplement and the owner started Bennie on that. Although vitamin E is not toxic in high doses since it is water soluble, selenium given in too high doses can cause toxicity. A deficiency of selenium can lead to muscle myopathy and weakness.
After one week of medications the owner reports that Bennie seems much improved. It will take weeks for his vitamin E and selenium levels to rise to normal range. I will recheck him in a couple months to examine and repeat the blood work!