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Generalized Inflammatory Muscle Diseases in Dogs

Polymositis and Dermatomyositis in Dogs

Polymositis and dermatomyositis are both generalized disorders characterized by inflammation of a dog’s muscles. Polymyositis specifically entails skeletal muscle damage due to inflammation, without pus formation, while dermatomyositis presents as a form of polymyositis accompanied by distinctive skin lesions.

Several dog breeds, such as Newfoundlands and Boxers, can be susceptible to polymositis, whereas dermatomyositis is commonly observed in rough-coated Collies, Shetland Sheepdogs, and Australian Cattle Dogs.

Symptoms and Types

  • Stiff-stilted gait
  • Muscle swelling
  • Muscle weakness
  • Muscle pain, especially upon touch
  • Exercise intolerance
  • Enlarged esophagus (megaesophagus)
  • Regurgitation
  • Skin lesions (specifically in dermatomyositis)


  • Immune-mediated infections
  • Drugs
  • Cancer


To diagnose polymositis and dermatomyositis, you’ll need to provide a comprehensive history of your dog’s health, detailing the onset and characteristics of the symptoms. The veterinarian will then perform a thorough physical examination, along with a biochemistry profile, urinalysis, complete blood count, and tests to measure levels of creatine kinase enzyme, which is typically present in the brain, muscles, and other tissues, to assess muscular damage.

Additionally, a sample of muscle will be collected for further evaluation by a veterinary pathologist, which is a crucial test for diagnosing polymyositis.

In cases where dogs experience regurgitation, thoracic X-rays will be conducted to examine the esophagus for dilation or to identify any tumors present. Surgery may be necessary if tumors are detected.


Treatment for polymositis and dermatomyositis typically involves the use of corticosteroids to suppress an overactive immune system, which could be an underlying factor. Antibiotics may also be prescribed to combat any concurrent infections. In cases of severe immune-mediated diseases, long-term corticosteroid therapy may be necessary for management.

Living and Management

For effective living and management of polymositis and dermatomyositis, it’s important to gradually increase your pet’s activity level as muscle inflammation subsides, aiming to improve muscle strength. Dogs with an enlarged esophagus (megaesophagus) will need special feeding techniques, which your veterinarian will guide you through. This may involve elevating feeding and incorporating various foods into the dog’s diet, particularly those with different consistencies.

In cases of severe regurgitation, your veterinarian may opt to insert a feeding tube into the dog’s stomach to ensure proper nutrition. They will provide instructions on how to use the feeding tube correctly and assist you in establishing a feeding schedule. Moreover, providing good supportive care is essential to prevent skin wounds and ulcers in non-emergency patients.

Fortunately, dogs with polymositis and dermatomyositis stemming from immune-mediated causes generally have a favorable prognosis. However, if cancer is identified as the underlying cause, the prognosis is typically poor.

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