for Lyme or equine protozoal myeloencephalitis. Running serologic tests for Lyme and EPM does not help you decide if the horse is neurologic or lame. Just because a lab test is positive or negative should not affect your clinical evaluation.”
Her message to horse owners was to allow your veterinarian to conduct specific physical tests and take a good history from you, your barn manager and/or your trainer in order to determine onset of clinical signs and gait abnormalities, when they occur, if they are affected by the administration of NSAIDs, and if they happen all the time or are irregular in their appearance.
“If an abnormal gait is recognized, but its origin is not clear, the next step is often diagnostic local or regional analgesia to see if the abnormal gait will ‘block out’, in which case musculoskeletal disease is assumed,” said Johnson. “If the abnormal gait is not considered ‘blockable,’ involves multiple limbs, or there are other reasons not to perform diagnostic analgesia, a systemic analgesia trial with phenylbutazone or similar non-steroidal anti-inflammatory drug might yield useful information. Repeated neurologic and lameness examinations are important, particularly after analgesia trials. In most cases, the appropriate diagnostic path will be identified at this point.”
Johnson reminded veterinarians and horse owners that a horse might have lameness and mild neurologic disease. “Sometimes it is easier to get rid of lameness to see how much that is contributing to problem,” she said.
“I realize there are horses with mild neurologic disease that are doing their current jobs well,” she added. “Hunters, jumpers and dressage horses can do their jobs up to a certain point with lowlevel neurologic deficits. Then if they develop lameness, it might be because of a new physical problem rather than the long-standing, low-level neurologic problem. That horse might have been that way neurologically for years.”
For EPM, Johnson said there are varying opinions among experts as to the best way to diagnose, treat and potentially prevent disease. “The diagnosis is based on three principles: compatible clinical signs with the disease; exclusion of other diseases; and proof of exposure,” she said. She also reminded horse owners that if the horse gets better on phenylbutazone, then it’s not EPM.
She said that current best practice for diagnostic testing for active EPM is for your veterinarian to submit serum and CSF for quantitative testing and calculation of a serum: CSF titer ratio.