Wobblers syndrome, or "Wobblers", is a neurological disease of horses that causes compression of the spinal cord, resulting in ataxia involving all four legs. There are over 14 different names used to describe the disease, mainly caused by confusion as to the underlying mechanisms involved with its onset. Some of the most commonly used names include CVM - cervical vertebral malformation, CVCM - cervical vertebral compressive myelopathy, CVI - cervical vertebral instability, and CSM - cervical stenotic myelopathy.
Clinical signs of wobblers can be identified in horses at an early age, in some instances before 3 months of age. Wobblers can also occur in older horses, caused by arthritic changes involving the articular process joints and intervertebral bodies. In many affected horses, the onset of clinical signs are acute, despite the slow progressive nature of arthritis. Horses with wobblers are often described by their owners as acting 'increasingly clumsy' or "drunk". The most common signs observed in affected horses include symmetric ataxia, paresis, and spasticity involving all four legs, but most pronounced in the pelvic limbs. These horses often routinely loose coordination and have an uneven stride length and height.
When neurological disease is suspected by your veterinarian, they will usually conduct a neurological examination on the horse. A neurological examination consists of a serious of mini tests used by veterinarians to better assess the type of neurological involvement. These tests include:
- Observation of the horse walking in a straight line: A test used to assess for signs of weakness, such as stumbling, dropping of the hip during the stride, dragging the toe, knuckling, varying stride length, swaying of the limbs or body (truncal sway), or floating of the limbs in the air.
- Observation of the horse walking in a tight circle: A test used to assess for the presence of outward swaying of the pelvic limb on the outside of the circle. The horse's head is usually kept elevated while walking, in order to exacerbate the signs and may cause the horse to start pacing.
- Tail-pull test: A test used to assess pelvic limb strength in the horse. Your veterinarian will pull the horse's tail a special way, while the it is standing at rest as well as while walking.
- Observation during walking backwards: A test used to observe whether the horse is having a difficult time backing up, as horses with spinal cord damage often can only drag the limbs backward slowly, and are usually unable to back up without difficulty.
Wobblers is thought to be a multifactorial disease, consisting of genetic predisposition and environmental influences (such as nutritional balance, rapid growth, abnormal biomechanical forces, and physical trauma.
The type of spinal cord compression that occurs in horses with wobblers can be dynamic or static:
Wobblers Vs. Equine Protozoal Myeloencephalitis (EPM)
- Dynamic compression: Tends to affect young horses between six months and two years of age. It is caused by abnormal bone development of the first four vertebrae and occurs only when the horse flexes or extends its neck. This form usually affects the hindlimbs more severely but is noted to occur in all four limbs.
- Static compression: It is caused by bone and soft tissue abnormalities and usually involves the fifth and seventh cervical vertebrae. This form of compression generally affects the horse's forelimbs more severely.
Clinical signs of horses with Equine Protozoal Myeloencephalitis (EPM)
may appear similar to Wobblers. Both diseases cause spinal ataxia, however many horses with EPM have asymmetric ataxia as well as additional lower motor neuron signs (muscle atrophy), and signs of brain and brainstem involvement (head tilt, facial paralysis, cranial nerve signs, blindness).
Wobblers Vs. Equine Herpes Myeloencephalopathy (EHM)
Equine Herpes Myeloencephalopathy (EHM) is a neurologic manifestation of Equine Herpesvirus-1 infection. Clinical signs of EHM can sometimes appear very similar to Wobblers. However, when horses are affected by EHM they will often usually also have a history of fever, along with weakness, symmetric ataxia (which frequently ascends up the pelvic limbs), poor tail tone, bladder dysfunction with urinary incontinence and sometimes will progress to recumbency and death. Usually with EHM, multiple horses are affected at or near the same time. With wobblers, usually only one horse is affected.
The treatment goal of medical management of horses with wobblers is to minimize swelling and inflammation in the spinal cord.