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Polymositis and Dermatomyositis in Cats

Polymositis and dermatomyositis are both generalized disorders which involve the inflammation of the cat's muscles. More specifically, polymyositis involves skeletal muscle damage due to inflammation, but with no pus formation, whereas dermatomyositis is a form of polymyositis in which characteristic skin lesions are also seen.

These disorders are rarely seen in cats and are more common in dogs.

Symptoms and Types

• Stiff-stilted gait
• Muscle swelling
• Muscle weakness
• Muscle pain (especially when muscles are touched)
• Exercise intolerance
• Enlarged esophagus (megaesophagus)
• Regurgitation
• Skin lesions (in dermatomyositis)

Causes

• Immune-mediated infections
• Drugs
• Cancer

Diagnosis

You will need to give a thorough history of your cat’s health, including the onset and nature of the symptoms. The veterinarian will then conduct a complete physical examination as well as a biochemistry profile, urinalysis, complete blood count, and tests to evaluate levels of creatine kinase enzyme -- normally found in the brain, muscles, and other tissues -- to assess muscular damage.

He or she will also collect a sample of the muscle to send to a veterinary pathologist for further evaluation. This is the single most important test for diagnosing polymyositis.

In cats with regurgitation, thoracic X-rays will help evaluate the esophagus for dilatation or identify tumor(s) within the esophagus. Surgery may be required if tumor(s) are found.

Treatment

Corticosteroids are typically used to suppress overactive active immune system, which may be an underlying factor. In addition, antibiotics are prescribed to fight off infection. Long-term corticosteroids treatment may be required in cats with severe immune-mediate diseases.

Living and Management

As muscle inflammation decreases, you will need to increase your pet's activity level to improve muscle strength. Cats with an enlarged esophagus (megaesophagus) will require special feeding techniques. You will briefed about elevating feeding and adding various foods to the cat's diet, especially foods of different consistencies. In cases of severe regurgitation, your veterinarian will place a feeding tube into the cat's stomach to ensure proper nutrition. He or she will also show you how to use the feeding tube correctly, and will assist in setting up a feeding schedule. In addition, good supportive care is required to prevent skin wounds and ulcers in non-emergency patients.

Fortunately, cats with polymositis and dermatomyositis due to immune-mediated causes have a good prognosis. If cancer is the underlying cause of the diseases, however, prognosis is poor.