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Non-inflammatory Hereditary Myotonia in Cats

Non-inflammatory hereditary myotonia is a muscle disease characterized by persistent contraction or delayed relaxation of muscles, especially during movement. Although it can be acquired later in life -- often experimentally induced with ingestion of herbicides -- this article pertains to congenital myotonia.

Symptoms and Types

The symptoms below are commonly associated with non-inflammatory hereditary myotonia; they may improve after exercise and/or worsen due to the cold:

• Voice change
• Muscle stiffness
• Difficulty breathing
• Difficulty rising or moving
• Difficulty swallowing (dysphagia)
• Regurgitation, especially after eating
• Tongue may protrude from mouth

Causes

This type of non-inflammatory myopathy is hereditary; i.e., it is inherited by a mother and/or father with the same sarcolemmal defect, which affects the cell membrane of a muscle cell.

Diagnosis

You will need to give a thorough history of your cat’s health, including the onset and nature of the symptoms, to your veterinarian. He or she will then conduct a complete physical examination, as well as a biochemistry profile, urinalysis, and complete blood count (CBC). Creatine kinase enzyme levels may be elevated due to the dystrophin deficiency. Liver enzymes are also elevated in cats with this disorder.

During the examination, your veterinarian will tap on the surface of the cat's tongue, both while conscious and while anesthetized. Such tapping produce sustained dimpling on the surface of tongue, which will provide a clue for diagnosis.

Treatment

Although there is no specific course of treatment for non-inflammatory hereditary myotonia, there are certain medications (procainamide, quinidine, phenytoin, mexiletine) that help in decreasing the muscular stiffness and regurgitation. This, however, does not improve the abnormal gait associated with the disorder.

Living and Management

Discourage your cat from strenuous activities or exercise that may increase its respiration, and avoid cold, which may exacerbate the symptoms. Unfortunately, even with treatment, the overall prognosis of a cat with non-inflammatory hereditary myotonia is very poor. Your veterinarian will also recommend against breeding the cat to prevent further progression of the disease to the next generation.