Meddleton Equine Hospital

This may seem to be an odd question, but neurological diseases caused by spinal cord damage, especially when mild, can be very difficult to differentiate from certain lameness problems.  Both can cause many of the same signs or performance problems.  This can be complicated by the fact that horses with neurologic disease often move and carry themselves abnormally; this can result in painful orthopedic conditions as the horse attempts to compensate. Additionally, these horses are often more accident-prone, sometimes leading to further musculo-skeletal injuries. 

Neurological Diseases such as “Wobbler” Syndrome and EPM (Equine Protozoal Myeloencephalitis), trauma to the neck or back, tumors or abscesses compressing the spinal cord, Equine Herpes Virus infection, West Nile Virus infection, and other less common conditions can cause severe neurological deficits, or in their more mild forms, can cause performance problems.  Horses that have recovered from WNV, EPM, or trauma can have residual deficits that show up as performance problems.

Wobbler Syndrome

The term “Wobbler” is used to describe a syndrome of weakness and ataxia (incoordination) that is caused by compression of the cervical (neck) spinal cord. The most common causes are either cervical instability due to malformation of the cervical vertebrae in young horses, or static compression due to arthritis in older horses.

EPM

Equine Protozoal Myeloencephalitis (EPM) is caused by protozoa that are carried by Opossum, ingested by horses, and then migrate to the spinal cord.  The signs of EPM depend on where in the spinal cord the protozoa establish themselves and start to damage the cord.  The hallmarks of EPM are that the signs are highly variable, usually asymmetrical, the horse is ataxic (incoordinated), and there is usually muscle atrophy.

Signs of lameness and neurologic problems

Some of the signs you might see with bilateral hindlimb lameness and spinal cord disease, such as “Wobbler” syndrome and EPM, include the following:  A change in performance, stiff or bouncy (poor quality) canter, difficulty taking and holding the correct lead, difficulty balancing in the counter canter, stumbling, dropping out behind, resistance in the bit / bridle, resistance to collection, lack of impulsion, feeling a lack of connection between the front and rear end of the horse, hesitance in a portion of the stride, poor cadence or rhythm, difficulty in tracking straight, inconsistent foot landing, toe dragging, abnormal hoof wear, and difficulty sticking the halt.

Proprioception is the ability to know where their body parts are without having to see them. This relies on information relayed from the body to the brain via the spinal cord. Proprioception is what is altered in diseases affecting the spinal cord. Spinal cord disease also results in muscle weakness. It can be difficult to determine whether a horse’s change in gait or posture is due to pain, weakness, or proprioceptive deficits.  This is the challenge that your Veterinarian faces in sorting out the cause of your horses performance problem.

Trial Treatment

If a horse gets significantly better after a course of a non-steroidal anti inflammatory drug (i.e. Bute), or if it is consistently worse with joint flexion tests, then the problem is likely pain and a thorough lameness exam is warranted.  However, negative flexion tests or failure to improve on pain medication may be an indication of neurological disease. This is especially true for young horses beginning training or older athletes. That being said, it is important to remember that hindlimb lameness and musculoskeletal issues of the lower back are much more common than spinal cord disease.

Your veterinarian will be able to determine whether a lameness exam, neurological exam, or both are needed. As is the case with musculoskeletal injuries, the prognosis for successful treatment of spinal cord disease is best when treated early. Do not hesitate to contact your veterinarian if you notice a change in your horse’s gait or posture.