Your veterinarian can perform a detailed examination to differentiate between gait asymmetry caused by musculoskeletal pain and neurologic disease. | Shelley PaulsonWhile trotting around the arena, you feel your horse stumble behind. Hes done it before, but is it just weakness? A patch of deep footing? Or could it be something more serious such as a neurologic condition? Musculoskeletal and neurologic lameness can be difficult to differentiate, but with a thorough exam and appropriate diagnostics, veterinarians can often determine where the problem lies and how to treat it.Signs of Neurologic Disease in HorsesOne key concept helps guide that process: A neurologic horses gait is irregularly irregular, while a lame horses gait is regularly irregular, says Stephen Reed, DVM, Dipl. ACVIM, of Rood & Riddle Equine Hospital in Lexington, Kentucky. A neurologic horse often shows proprioceptive ataxia, meaning poor coordination and reduced awareness of where his limbs are in space. Ataxia is an abnormal sway of the limb in the air, abnormal posture or positioning when it lands, circumduction when turning in small circles with a wide outward turn with one of the limbs, and pacing.These horses might also show signs of weakness, such as tripping, dragging a foot, or stumbling. Damage to the spinal cord can manifest as spastic or weak limb movements that result in tripping or an abnormal gait that might be mistaken for orthopedic lameness, says Amy L. Johnson, DVM, Dipl. ACVIM-LAIM, of the University of Pennsylvanias New Bolton Center, in Kennett Square. These steps that can look in some ways like a lameness, but its not in one leg, its in all four legs, so it can be really hard to pinpoint. The horses can feel very off, but the rider or the observer cant pick a leg because each leg is doing something different, and its a very irregular gait. There also is often some weakness or buckling thats common with neurologic disease.Typically, a horse experiences musculoskeletal lameness due to pain from an injury site. In contrast, a neurologic horse might not appear painful and, for that reason, a veterinarian might recommend a short phenylbutazone (Bute, a non-steroidal anti-inflammatory drug) trial. Improvement suggests a musculoskeletal cause.Diagnosing Neurologic Disease in HorsesA standard lameness examincluding hoof testing and nerve blocking progressing up the limbcan help your veterinarian localize pain. Diagnostic imaging such as radiographs, nuclear scintigraphy (bone scans), and ultrasound can help pinpoint the source of pain. If you get all the way up to the shoulder and you havent been able to make the horse normal, you have what I would call an unblockable lameness, says Reed, pointing toward a possible neurologic cause.In those cases a veterinarian might proceed with a neurologic exam, which includes walking the horse in a tight circle and in a zigzag pattern, pulling on the tail to assess strength and response, and carefully observing limb placement. If a horse appears incoordinated, has delayed reactions, or leans excessively, those findings raise concern for neurologic disease.Common Equine Neurologic DiseasesEquine protozoal myeloencephalitis (EPM) affects the spinal cord and causes asymmetric gait abnormalities that can mimic musculoskeletal lameness. The protozoa responsible for EPM can affect multiple areas of the nervous system. It is not unusual when you have those kinds of infections to also get muscle wasting, says Reed. When you have muscle atrophy, the hallmark clinical sign is weakness.Johnson also sees horses with an abnormal hind-end gait referred for suspected pelvic fractures after a presumed fall. During sedation, technicians might notice the horse appears wobbly and, after a clean bone scan, a cerebrospinal fluid tap ultimately confirms EPM.Johnson says some of the most challenging neurologic cases affect only one limb. Those are ones where you have either peripheral nerve involvement or a specific area of the spinal cord that houses the cell bodies that contribute to the peripheral nerve, she explains. When those nerves are affected, the horse develops a gait abnormality localized to one limb; EPM is the most notorious neurologic disease to do that.Cervical stenosis, commonly referred to as Wobbler syndrome, can also cause signs of neurologic disease. This developmental condition compresses the spinal cord in the neck, leading to incoordination and ataxia.Johnson also notes that neck arthritis or a condition called foraminal stenosis can cause nerve compression, pain, or lameness. Foraminal stenosis refers to narrowing of the opening, or foramen, where nerve roots exit the spinal cord and form the spinal nerves that innervate the front limbs. Traumatic nerve injury or even a tumor putting pressure on a nerve can create similar clinical signs.Diagnosing Equine Neurologic Conditions With TechnologyJohnson says veterinarians have growing interest in objective ways to identify mild ataxia because diagnosis currently relies heavily on subjective assessment. Scientists are examining electrodiagnostic techniques that measure signal delays between the brain and limbsparticularly through the neck regionthough they are not yet widely available. There is a potential means to put a number on things and document that it truly is a spinal cord problem, she says. That type of electrodiagnostic technology is being actively investigated to assist in both the differentiation and quantitation of neurologic disease to determine whether the spinal cord is transmitting information correctly and, if not, how slowly its functioning.Artificial-intelligence-powered equine gait analysis apps already detect asymmetry and provide stride-by-stride data, and Johnson says they could eventually support neurologic assessment as well. Its just because of the irregularity and the unpredictability of the neurologic gait that it hasnt been as easy to use this type of AI compared to its routine use for a lameness thats more consistent, she explains.Electrodiagnostic testing to evaluate muscle and nerve function, such as transcranial electrical and transcranial magnetic stimulation, represents another sophisticated diagnostic tool, Reed adds. But thats going to be something thats done to each individual horse, as opposed to something that you would look at and utilize when trying to assess a gait, say during an exam, he notes. This would be an ancillary test you do after the exam.Take-Home MessagePain-related and neurologic gait abnormalities often look similar, but a veterinarian can usually sort them out with a careful exam. As emerging tools such as AI-based gait analysis advance, they might further support diagnostic decision-making. Reed says owners should remember an irregularly irregular gait often reflects neurologic disease, while a regularly irregular pattern typically indicates a musculoskeletal cause.