What is Ataxia?
The term ataxia comes from the Greek meaning “without order”. Ataxia refers to a lack of normal coordination of movement. There are different types of ataxia, but here we are referring to cerebellar ataxia. The cerebellum (the “little brain”) is the portion of the brain that fine-tunes movement.
Affected dogs might have a “drunken”, “staggering” gait, and frequently have a “goose stepping” movement of the front limbs. They may move well in a straight line, but stumble or fall when making fast turns, climbing stairs, or attempting to catch a ball. A quick movement such as shaking the head may precipitate a brief dizzy spell where the dog stiffens, falls, and develops a rapid twitching of the eyes called nystagmus.
What does Cerebellar Ataxia look like?
Cerebellar ataxia can encompass a variety of different problems with coordination and balance. These will include a staggering gait often with a prominent goose stepping of the front limbs, crossing over of the limbs, and balance problems.
The goose-stepping movements of the front limbs are referred to as dysmetria (from the Greek meaning poorly measured) or more specifically hypermetria referring to the exaggeration of the movement. A normal dog barely picks the foot up of the ground to move it forward as efficiently as possible. An ataxic dog, on the other hand, may pick the foot past their elbow which means they then have to bring to foot down quickly to get it on the ground before they pick up the opposite foot.
The poorly measured limb movements combine with a similar difficulty keeping the spine stable (truncal ataxia) to produce the typical drunken, staggering gait of a dog with cerebellar ataxia. The dog may do OK when walking a straight line, but will cross the feet, stumble, and weave when making a sudden turn. Click on the picture to see a short video clip showing ataxic movements.
A tendency to lose their balance is also apparent when a dog with ataxia makes a sudden turn. Sudden head movements, such as shaking the head, may precipitate a dizzy spell that will cause the dog to lose their balance, stretch out their legs, and fall to the ground. Such dizzy spells may be accompanied by a twitching of the eyes called nystagmus. This twitching can be side-to-side or circular, but is most commonly up-and-down. Such episodes may be misinterpreted as a seizure or a stroke. Click on the top picture to see the response to head-shaking and the bottom picture to see the eye movements.
Another sign sometimes seen with cerebellar disease is tremors. These differ from the typical shaking that a dog might do if cold or nervous. A dog with cerebellar problems will not shake when resting, If, however, they are trying very hard to make a movement or focus on something, they will develop a wobbling back and forth. This is often most dramatic when they are hungry and trying to focus on their food. Often the tremor results in the dog banging their nose into the food and making it difficult for them to get enough food.
In some breeds, the cerebellar ataxia is the only symptom. These dogs can often live with their disability. In some breeds, such as the Kerry Blue Terriers and Chinese Crested Dogs, the disease progresses to involve other motor systems. These dogs become incapacitated by their disease. Still other breeds, such as the Coton de Tulear dogs, the pups are severely affected from birth.
What causes Cerebellar Ataxia?
Cerebellar ataxia is cause by problem in the part of the brain called the cerebellum. Any disease that damages the cerebellum can produce the signs of ataxia. The first step in helping any dog with ataxia is to perform diagnostic tests to rule out other causes besides hereditary disease, such as brain tumors, infections, or congenital malformations. This is a critical step since some of these other conditions may be readily treatable. An MRI scan of the brain can show the shrinkage of the cerebellum that occurs with hereditary ataxia.
In hereditary ataxias, a genetic defect leads to degeneration of the cerebellum. There are many variations on this disease. In some, only a limited portion of the cerebellum degenerates and the dogs can still walk. In the most common type of hereditary ataxia, only one cell type in the cerebellum, the Purkinje cells, degenerate. In other breeds, additional portions of the movement systems in the brain degenerate. In dogs with these more extensive degenerations, the signs will be more severe. The more severely affected dogs are incapacitated by their disease, while more mildly affected dogs can live with their disabilities.
How is it inherited?
Most of the hereditary ataxias in dogs appear to be autosomal recessive traits. In recessive traits, a dog can carry the gene responsible, but not be affected. If two carriers of the gene are bred, however, affected pups can result. Identifying carriers can be difficult, especially when the disease does not show up until later in life.
What breeds are affected?
Many different breeds have been affected with this condition. As with any genetic disease, it can be difficult for even the most conscientious breeder to completely eliminate the condition from the breed until a DNA test is developed. Several breed clubs, with the help of the Canine Health Foundation of the American Kennel Club, have funded research to develop such DNA tests.
How to help
If you own a dog that you suspect has hereditary ataxia, please contact us. You will still need to see your veterinarian and if necessary consult with a veterinary neurologist to be sure of the diagnosis. If they confirm that this could be hereditary ataxia, you can help with search for the genes responsible for the disease so that future dog lovers will not have to face the prospect of seeing their companion afflicted with these diseases.