Generalized Inflammatory Muscle Diseases in Dogs

Polymositis and Dermatomyositis in Dogs

Polymositis and dermatomyositis are both generalized disorders which involve the inflammation of the dog'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.

Various breeds of dog, including Newfoundland and boxer, may be affected by polymositis, while dermatomyositis is typically reported in rough-coated collies, Shetland sheepdogs, and Australian cattle 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 dog’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 dogs 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 an 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 dogs 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. Dogs with an enlarged esophagus (megaesophagus) will require special feeding techniques. You will briefed about elevating feeding and adding various foods to the dog's diet, especially foods of different consistencies. In cases of severe regurgitation, your veterinarian will place a feeding tube into the dog'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, dogs 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.