Polymyositis in dogs

Area of Science:

• Veterinary Medicine
• Canine Pathology
• Neuromuscular Diseases

Background:

• Polymyositis is an inflammatory muscle disease affecting dogs.
• Diagnosis can be challenging due to variable clinical signs and laboratory findings.

Purpose of the Study:

• To describe the diagnostic factors, clinical signs, and treatment outcomes in nine dogs diagnosed with polymyositis.
• To evaluate the utility of serum muscle enzyme concentrations and electromyography in diagnosing canine polymyositis.

Main Methods:

• Diagnosis based on clinical signs (muscle pain/weakness), serum muscle enzymes, electromyography, and histopathology.
• Clinical signs, diagnostic test results, and treatment responses were recorded.
• Prednisone was administered at 2.2 mg/kg once daily.

Main Results:

• Nine dogs diagnosed with polymyositis.
• Clinical signs included pain, weakness, stilted gait, and pyrexia.
• Elevated serum muscle enzymes were present in only three dogs, with no clear correlation to disease severity.
• Electromyography showed characteristic changes.
• Histopathology revealed muscle degeneration, inflammation, and regeneration.
• Prednisone was effective in four dogs.
• Complications included aspiration pneumonia secondary to megaesophagus in three dogs.

Conclusions:

• Canine polymyositis diagnosis requires a combination of clinical, electrodiagnostic, and histopathologic findings.
• Serum muscle enzyme levels may not reliably reflect disease severity.
• Prednisone can be an effective treatment, but potential complications should be monitored.