What is ataxia?
Ataxia is incoordination within the nervous system. The abnormal movement can occur in the legs, the head, the body, or all three. There are several forms of ataxia, depending on where in the nervous system the abnormality occurs.
The first type involves a failure of awareness of where the limbs are in space. This unconscious body awareness is called proprioception, and when there is a proprioceptive abnormality, movement is difficult and looks quite abnormal. A proprioceptive defect most commonly occurs when pressure is placed on the spinal cord from a bulging intervertebral disk or tumor, from a tumor within the spinal cord itself. It can also occur from a bleeding blood vessel within the spinal cord or a failure of the nerve conduction capacity of the spinal cord.
The second type of ataxia occurs because of abnormal function of the inner ear or brainstem, which causes a disruption in balance. This type of ataxia is called a vestibular abnormality, or vestibular syndrome.
Finally, the third source of ataxia is localized to the cerebellum, the part of the brain where fine motor movement is coordinated. These dogs often look normal at rest, but when they start to move, their limb movements are quite exaggerated. They also typically also have head tremors.
What are some characteristics of the various types of ataxia?
The most common sign of ataxia, regardless of cause, is an abnormal gait in which the dog is very unsteady on his feet. With a spinal cord lesion, the toes may drag on the ground as the dog walks, wearing off the ends of the toenails.
With a vestibular disorder, it is also common to see abnormal movement of the eyes, typically drifting to the side. Dogs will often stand with their feet wide apart, in an effort to stay upright. They may have a head tilt toward the side of the lesion in vestibular syndrome. Also, with vestibular syndrome, the dog may be unable to stand and may roll toward the side of the lesion, sometimes rolling over completely, time and time again.
If the ataxia is caused by a lesion in the cerebellum, the dog will walk with an exaggerated “goose-stepping” gait called hypermetria.
What causes ataxia?
There are many different causes of ataxia, depending on where the problem is located.
Spinal cord causes of ataxia:
- Loss of spinal cord tissue (called degenerative myelopathy)
- A “stroke” to the spinal cord (called fibrocartilaginous embolus or FCE)
- Structural/developmental abnormality of the spine or spinal cord
- Tumors in the spine or spinal cord
- Infection in the vertebrae or intervertebral discs
- Inflammation of the spinal cord
- Trauma to the spinal cord
- Instability in the spine causing pressure on the spinal cord
- Narrowing of the spinal canal that protects the spinal cord
Vestibular causes of ataxia (inner ear):
- Middle or inner ear infection
- Geriatric vestibular disease in which the precise cause may never be identified (also called “idiopathic”)
- Hypothyroidism
- Tumors in the ear or skull
- Trauma to the head/ear
Vestibular causes of ataxia (brainstem):
- Infection (e.g., canine distemper virus)
- Inflammation (the cause of which may or may not be uncovered)
- Thiamine deficiency (uncommon with current nutritional products)
- Metronidazole (an antibiotic) toxicity
Cerebellar causes of ataxia:
- Degenerative changes in the cerebellum
- Structural abnormalities (e.g., underdevelopment or malformation of the cerebellum or the surrounding skull)
- Brain tumor
- Infection or inflammation in the brain
- Metronidazole (an antibiotic) toxicity
Miscellaneous causes of ataxia:
- A red blood cell count that is too low or too high
- Low levels of potassium, calcium, or glucose (blood sugar)
- Heart/circulation and/or respiratory diseases
What kinds of treatments are used for dogs experiencing ataxia?
Treatment of ataxia will be influenced by the root cause. Pain management, supportive care (such as anti-nausea medications), and making the environment safe (e.g., preventing access to stairs) are cornerstones of ataxia treatment. Regular reassessments will be scheduled to monitor the progress of recovery. Some causes of ataxia cannot be cured, and these dogs typically experience clinical signs that progress and may eventually result in the need for euthanasia.
