Hello there! Welcome back to my corner. When it comes to neurological disease in the horse, there are two syndromes you should be familiar with. They are both diseases caused by spinal cord compression in the neck, and can exhibit symptoms very similar to EPM, West Nile Virus, and other infectious causes of neurologic disease. Cervical stenotic myelopathy (CSM), formerly known as “Wobbler’s syndrome,” exhibits two forms – type I and type II. This week we will discuss Type I CSM, which is the “classic Wobbler’s,” and next week we will discuss type II – seen in older horses as a result of neck (cervical) arthritis.
Type I CSM, also called Cervical Vertebral Malformation, is most commonly seen in horses less than five years of age. In every species, there is a canal that present in each vertebra, called the spinal canal, that houses the spinal cord. These holes must line up and be of sufficient width to allow the spinal cord to run straight through the spinal column without compression from the bony tunnel. This is exactly what goes wrong in horse with Type I CSM. Sometimes the canal in the vertebra narrows, sometimes it is shaped like a cone, or it can be elongated. These changes are a result of a developmental orthopedic disease in the vertebra, in the same group as OCD, contracted tendons, and bone cysts. As a result, the horse has compression of the nerves that run along the outside of the spinal cord to their legs. In general, the nerve compression that occurs is worse in a flexed neck position, and so we call the narrowing “dynamic,” or changing. Rapid growth and large size are risk factors for this type of CSM, as are high protein and caloric intakes. There may be a genetic predisposition for this disorder as well. Thoroughbreds, Warmbloods, and Tennessee Walking horses are significantly more likely to be affected than Quarter horses, Standardbreds, and Arabians.
Clinical signs often manifest first as evidence of weakness in the hind end. This is because the nerves running to the hind legs are to the outside of the nerves running to the front legs in the spinal cord. Ataxia, spasticity of the limbs, and weakness may start insidiously or suddenly. Sometimes a history of a fall confuses the diagnosis (was the fall the cause or result?), and clumsiness and tripping is commonly reported. Changes may first be noticed by your farrier when he is trying to trim the back feet. A pacing gait may also be present. Diagnosis is based on a complete neurologic exam where the neurologic deficit is localized to the neck, followed by neck radiographs. Sometimes it is necessary to inject contrast dye into the space outside the spinal cord (contrast myelogram), and then radiographs show a narrowed or “pinched off” area where the dye can’t pass through the compressed area. Often the CSF analysis is normal.
Prevention of Type I CSM is aimed at limiting protein and caloric intake to regulate growth. Suspected horses less than a year should be weaned and placed on a “Paced Diet,” including free choice grass hay and limited amounts of growth diet and/or ration balancer to provide necessary vitamins and minerals. Foals should be confined to a stall or small paddock to restrict exercise, certainly not free-choice pasture. Intra-articular (joint) injections with steroids can be performed on the affected neck joints under ultrasound guidance, providing symptomatic relief (will be discussed in more detail next week). Finally, surgical correction can be performed for affected horses. A metallic (steel or titanium) cylinder or basket is placed between the vertebrae – the goal is to induce arthritis, fusing the joint between the neck vertebrae (as we fuse hock joints in cases of advanced arthritis). This makes the joint more stable and minimizes dynamic compression. It has been found to improve the neurologic status in 44-90% of horses with dynamic compression.
Please contact us if you would like more information on diagnosis, prevention, and treatment of CSM Type I. As always, may your litter box be clean, and your food bowl be full. Thanks for stopping by!