Polymyositis

Polymyositis (PM) is a rare idiopathic inflammatory myopathy characterized by chronic, symmetric, proximal muscle weakness and inflammation. It belongs to a group of acquired muscle diseases collectively known as inflammatory myopathies, which also includes dermatomyositis and inclusion body myositis. Polymyositis primarily affects skeletal muscles, leading to progressive weakness of the proximal muscles, particularly those of the hips, thighs, shoulders, upper arms, and neck. Patients typically experience difficulty with activities such as climbing stairs, rising from a seated position, lifting objects overhead, and in some cases swallowing (dysphagia) or breathing due to involvement of pharyngeal and respiratory muscles. The disease results from immune-mediated damage to muscle fibers, with cytotoxic T lymphocytes (CD8+ T cells) invading and destroying muscle tissue. Muscle biopsy characteristically shows endomysial inflammatory infiltrates surrounding and invading non-necrotic muscle fibers. Elevated serum creatine kinase (CK) levels, electromyographic abnormalities, and the presence of myositis-specific autoantibodies (such as anti-Jo-1, anti-SRP, and anti-Mi-2) support the diagnosis. Polymyositis can occur in isolation or in association with other autoimmune conditions, connective tissue diseases, or rarely with malignancy. Extramuscular manifestations may include interstitial lung disease, cardiac involvement (arrhythmias, myocarditis), arthralgia, and Raynaud phenomenon. Treatment of polymyositis is primarily immunosuppressive. First-line therapy consists of high-dose systemic corticosteroids (such as prednisone), which are effective in many patients. Steroid-sparing immunosuppressive agents, including methotrexate, azathioprine, mycophenolate mofetil, and tacrolimus, are commonly used as second-line therapies or in combination with corticosteroids. For refractory cases, intravenous immunoglobulin (IVIg) or rituximab may be considered. Physical therapy and rehabilitation play an important supportive role in maintaining muscle strength and function. While many patients respond to treatment, some experience chronic progressive disease or treatment-resistant weakness, and long-term outcomes vary.

Common questions about Polymyositis