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Anti-Jo-1 (most common, associated with lung involvement)
Anti-SRP, Anti-Mi-2, Anti-PL-7, Anti-PL-12 (less common)
Skeletal muscles (especially proximal muscles)
Sometimes lungs (in association with interstitial lung disease)
Esophagus (in cases with swallowing difficulty)
Polymyositis is a rare autoimmune muscle disease that causes chronic inflammation and weakness in the skeletal muscles, particularly those closest to the center of the body (like the thighs, hips, shoulders, and upper arms). It typically develops gradually and can make everyday tasks—like climbing stairs or lifting objects—more difficult over time.
It is one of a group of diseases called inflammatory myopathies and usually affects adults, especially those between 30 and 60 years old.
Muscle weakness (especially in hips, thighs, shoulders, upper arms, and neck)
Difficulty rising from a chair or climbing stairs
Fatigue after walking or standing
Trouble swallowing (dysphagia)
Muscle aches or tenderness (less common than weakness)
Low-grade fever or weight loss (in some cases)
Breathing problems if respiratory muscles are affected
Polymyositis is autoimmune, meaning the immune system attacks the body’s own muscle tissue.
While the exact cause is unknown, possible contributing factors include:
Genetic predisposition
Viral infections (e.g., HIV, HTLV-1, Coxsackievirus)
Other autoimmune diseases (e.g., lupus, scleroderma, rheumatoid arthritis)
Certain medications or toxins (rarely)
Blood tests: Elevated muscle enzymes (CK, aldolase), positive autoantibodies
EMG (electromyography): To detect muscle abnormalities
Muscle biopsy: Confirms inflammation and damage
MRI: Identifies areas of muscle inflammation
Autoantibody testing: May include anti-Jo-1 and other myositis-specific antibodies
Corticosteroids (e.g., prednisone) – first-line therapy
Immunosuppressants (e.g., methotrexate, azathioprine)
Physical and occupational therapy to maintain strength and function
IVIG or biologics (like rituximab) for resistant cases
Regular monitoring of lung and heart function if involved
Many patients respond well to treatment, especially when diagnosed early
May require long-term medication to control inflammation and prevent relapse
In some cases, permanent muscle weakness or disability can occur
Complications can include lung involvement (interstitial lung disease)
Roughly 1 to 8 people per 100,000
More common in women
Onset typically between 30–60 years of age
National Institute of Neurological Disorders and Stroke (NINDS). Polymyositis Information Page.
https://www.ninds.nih.gov/health-information/disorders/polymyositis
Dalakas MC. (2003). Polymyositis, dermatomyositis, and inclusion-body myositis. N Engl J Med.
https://doi.org/10.1056/NEJMra022450
Tiniakou E, Mammen AL. (2013). Idiopathic inflammatory myopathies and autoantibodies. Curr Opin Rheumatol.
https://doi.org/10.1097/BOR.0b013e32835aa7b7
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