My dog has been diagnosed with shaker dog syndrome. The veterinarian put her on steroids and a muscle relaxant. What is this disorder and what causes it?

An acquired tremor in young adult dogs.

Shaker dog syndrome is an acquired tremor that may occur in young adult dogs. Any breed and color of dog may develop this disorder. However, small breeds with white coats are at greater risk of developing it. West Highland white terriers, Maltese terriers and beagles are the breeds most commonly affected. The age of onset typically occurs between one and two years of age.

A tremor is a characteristic, abnormal set of repetitive movements that occurs when opposing muscle groups alternatingly contract and relax. The type of tremor in shaker dogs is an intention tremor, one that becomes worse with movement or attempted movement. Shaker dogs' entire bodies shake continually. The tremor gets worse when the affected dog experiences excitement or is handled.

The cause of shaker dog syndrome is unknown. It affects the cerebellum and the cerebellar nerve tracts. There are various theories concerning the cause of shaker dog syndrome. One proposes a disruption in the production of the neurotransmitter substances epinephrine and dopamine. These substances are made from tyrosine, an amino acid, in nerve cells. Theoretically an autoimmune-mediated process, in which the affected animal's body makes antibodies against these nerve cells, could destroy the cells that make these neurotransmitters. A genetic role in the underlying cause has also been proposed. To date, these and other theories concerning the cause have not been proven.

The tremor is often the only sign of shaker dog syndrome. Some affected dogs may be ataxic (have uncoordinated muscle movements) and have hypermetria (a form of ataxia characterized by intended movements that exceed the objective). Occasionally head tilt may be seen. Bloodwork is usually normal unless unrelated diseases are also present.

Shaker dog syndrome is treated with corticosteroid drugs (prednisone) and benzodiazepine tranquilizers (diazepam), either separately or in combination therapy. Corticosteroids suppress the underlying disease process, whatever its origin. Diazepam and other benzodiazepine drugs act as muscle relaxants and help calm the tremor. Treatment is not universally effective and relapses occasionally occur, which respond to repeated treatment.

10/13/03