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First Posted: July 17, 2007

Wobbles, Cervical Vertebral Malformation, Cervical Stenotic Myelopathy, Wobbler Syndrome

Video of Wobbler Syndrome Watch the hind legs carefully.

Cervical Vertebral Malformation, Cervical Stenotic Myelopathy
by Debora Johnson

Update: New treatment available for wobbles Wobbles Surgical Treatment

Wobbler Syndrome is a neurological condition. It usually presents itself in horses between the ages of 6 months and 4 years. Ataxia of the limbs is the most noticeable symptom of Wobbles Syndrome. non coordination of the limbs, changes in behavior, seizures, some depression, and youngsters off their feed are symptoms that are often seen. Signs of brain disease such as changes in behavior, seizures, or severe depression, are not evident.

Hind end ataxia is seen more than non coordination in the front limbs. However, weakness and non coordination are also seen in the front limbs. Weakness is seen on both sides of the body. It may be more pronounced on one side, but it is usually present on both sides. EPM presents with much the same symptoms, however, with EPM one side may be affected and not the other. To perform a small test on your horse, grasp his tail and his halter. Turn his head to his tail--his body is curled- and turn him in a tight circle. If your horse has trouble crossing his hid legs or front legs, and cannot make this tight turn, you probable have trouble. Do this in both directions as one side may affected and not the other. Asymmetry of ataxia is seen in Equine Protozoal Myelitis (EPM). Compression of the spinal cord down the horse's neck and back are usually the problem in Wobbles Syndrome. Often the vertebrae are unstable or not aligned properly. These problems usually occur in the horse's development stage. Sometimes you will hear Wobbles referred to as Cervical Vertebral Malformation or Cervical Semiotics Myelopathy.

Symptoms

The horse does not have the proper sense of his legs. This is called proprioception. The horse may fall. He may just be standing or walking and stumble or fall. Certainly, this often happens during training and exercise. The compression on the cervical spine causes the Lack of coordination. The condition is usually pre-existing from neurological dysfunction. The horse's neck is often inflexible. It may be visually crooked. As the horse impels forward the legs do not work in proper sequence. They appear to be off.

Causes

Abnormal bone development in the neck, in young horses, is a major cause of Wobbles. There are many reasons that this abnormal bone development may occur. Wobbles is not completely understood. Genetics is thought to be a factor.

Genetics An Inherited Risk
  • Rate of growth is affected by diet and genetics
  • Dietary factors affect the rate of growth and are important for maturation of bone
  • Hormones Male horses are at higher risk than female horses
  • Work or excessive exercise on immature bones
  • Young male thoroughbred horses are at particular risk for this condition, especially those that have gained weight rapidly during their first two years of life.

The spinal cord is not protected properly by the cervical vertebrae in the neck and along the horse's top line. The horse's movement can cause damage because of the abnormal bone formation or lack of bone formation. In Wobbler Syndrome, compression of the spinal cord, degeneration of the cord, and neurological implications all may be the cause of ataxia in the limbs.

For more information on ataxia: Ataxia in a Young Horse: A Matter of Time and Luck

Update:

"When faced with a horse exhibiting neuralgic disease, the importance of a thorough physical exam and diagnostic testing cannot be emphasized enough. Stephen Reed, DVM, Dipl. ACVIM, of Rood & Riddle Equine Hospital in Lexington, Ky., described selected equine neuralgic diseases during his presentation of the prestigious Milne Lecture at the 2008 American Association of Equine Practitioners Convention, held Dec. 6-10 in San Diego, Calif.

A review of selected neurological diseases affecting horses. Some elements of the exam include evaluating proprioception (the horse's awareness of where his feet are in space), gait changes, the presence of unusual gaits, and identifying the neuroanatomical location of an abnormality. He explained that proprioceptive deficits are the first signs of compressive lesions in the spinal cord, while deep pain sensation is the last function lost. While a horse's history is important, Reed's relies on a full exam. He begins with evaluating the horse's behavior and mental status, and examining the head and cranial nerves. Then he moves systematically along the body and limbs toward the tail, and finally assesses gait. The type of response is important--whether it be a deficiency, a "discharge," such as a stereotypic (continuous, repetitive, and serving no purpose) behavior, seizure, or spasm; or a "release," such as an exaggerated, weak, or ataxic (incoordinated) response. Gait evaluation is a critical part of the exam. All findings should be recorded, signs characterized, and attempts made to localize the lesion to help determine the cause.

The first condition Reed discussed is cervical vertebral stenotic myopathy (CVM), also known as wobbler syndrome. (Stenosis implies a narrowing of the vertebral canal.) This can be a developmental problem in young light-breed horses, or it can be an acquired problem in older horses (over 10 years) from osteoarthritis of the neck vertebral articular process joints (facets). Elongation of the dorsal laminae (the bony plates that form the roof of the vertebral canal) into the intervertebral space (between the vertebrae) can cause stenosis, requiring surgical correction. Compression in a wobbler most commonly occurs between cervical vertebrae 6 and 7 (C6-C7).

Osteochondrosis dissecans (OCD) of the facets is a common developmental cause of wobbler syndrome, and growth plate abnormalities (vertebral epiphysitis) can also narrow the canal. The vertebral column is sensitive to dietary imbalances, particularly of copper, which influences vertebral development, or excess energy, which causes rapid skeletal growth. This rapid growth influences vertebral development and the propensity for OCD. Often, wobbler syndrome changes in the axial skeleton occur in conjunction with developmental orthopedic disease in the limbs. Reed noted that conservative treatment of diet (protein and energy) and exercise restrictions might prove successful for young wobbler horses.

Malalignment of vertebrae can also cause CVM, especially at C2-C3. Such malalignment is unusual, but it tends to be associated with the fixed, high arch of head and neck seen in Saddlebreds or some Warmbloods.

Reed described the tenets of the approach used by Barrie Grant, DVM, MS, Dipl. ACVS, a veterinarian in Bonsall, Calif., known for his CVM treatment methods:

  • Keep the horse alive and treat the underlying cause when possible, as this might result in an amazing recovery.
  • Take an aggressive approach to achieving an accurate diagnosis, using spinal taps and myelograms (which involve injecting a contrast agent, which is a solution that shows up on X rays, into the spinal canal to reveal any compressive lesions of the spinal cord) as necessary.
  • Standing cervical (neck) radiographs can be performed; pay careful attention to vertebral anatomy and measurements.
  • A mildly ataxic horse might perform okay, and a horse that is lame might perform okay, but a horse that is both ataxic and lame neither can perform, nor is he safe to ride.
  • Sheared heels can be a general sign of ataxia, but typically a horse with wobbler syndrome has symmetric ataxia, weakness, or spasticity, most notably in the rear limbs. Toe dragging, stumbling, and outward excursion of the rear limbs are also typical signs. It is important to recognize that other musculoskeletal diseases can make a horse look ataxic, such as bilateral suspensory ligament desmitis or bilateral stifle OCD. It is possible for a horse to have several coexisting conditions.

A mildly ataxic horse might perform okay, and a horse that is lame might perform okay, but a horse that is both ataxic and lame neither can perform, nor is he safe to ride. Reed stressed the importance of addressing the situation early, as residual damage to neuromuscular tissue might not be resolved. He noted that patience is essential, and you should allow at least 18-24 months to realize the outcome with treatment. Physical therapy during rehabilitation improves the outcome. The intended use of the horse is important to consider when attempting treatment, and all measures should be taken to conduct follow-up exams to help ensure rider and horse safety. Genetic influences of wobbler syndrome are still under investigation. Research has shown breeding wobbler horses to other wobbler horses resulted in an increase in limb OCD occurrence, but this effort never reproduced a wobbler. This disease can affect horses of all ages, but if the horse is older than 10 years, he likely has an acquired ostearthritic problem. Breed distribution of wobbler-affected horses is as follows: 37% Thoroughbred, 25% Warmblood, 16% Quarter Horse, 21% other (including a fair number of Tennessee Walkers), and 1% pony."

For More Information:

Wobbler Syndrome in Horses - University of Kentucky
AAEP 2008 Milne Lecture: Neurology is Not a Euphemism for Necropsy
Wobbler Syndrome in Older Horses

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