My dog suddenly became unsteady on his feet, almost as though he was drunk. He was diagnosed him ataxia. What is that?
The word ataxia means incoordination within the nervous system. The abnormal movement can occur in the legs, the head, the torso, or all three.
There are several different forms of ataxia, depending on where in the nervous system the abnormality occurs. The first type is a failure of the unconscious awareness of where the limbs are located in space. This unconscious body awareness is called proprioception, and when there is a proprioceptive abnormality, movement is difficult and 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, from a bleeding blood vessel within the spinal cord, or a failure of the nerve conduction capacity of the spinal cord.
"There are several different forms of ataxia, depending on where in the nervous system the abnormality occurs."
The second type of ataxia occurs as a result of abnormal function of the inner ear or brainstem that 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 can be quite exaggerated and they typically also have head tremors.
What are some distinguishing characteristics of the various types of ataxia?
The most common sign of ataxia, regardless of the 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 from side to side. Dogs will often stand with their feet wide apart in an effort to stay upright. They may generally have a head tilt toward the side of the lesion in vestibular syndrome. Also, with vestibular syndrome, the dog may actually be unable to stand and may roll toward the side of the lesion, sometimes rolling completely over 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 potentially many different causes of ataxia, depending on where the problem is located. Spinal cord problems causing 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 which 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
- 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:
- Too low or too high red blood cell count
- 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, and making the environment safe (e.g., preventing access to stairs) are cornerstones of ataxia treatment. Regular reassessments will be scheduled in order 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.