What is the most common inflammatory myopathy in adults?

From the Guidelines

Dermatomyositis is the most common inflammatory myopathy in adults, characterized by skin rash and muscle weakness. This autoimmune condition causes progressive muscle weakness, primarily affecting the proximal muscles of the limbs, particularly the shoulders and hips. Patients typically present with difficulty climbing stairs, rising from chairs, or lifting objects above their heads. Diagnosis involves a combination of clinical evaluation, elevated muscle enzymes (particularly creatine kinase), electromyography, and muscle biopsy showing inflammatory infiltrates and muscle fiber degeneration.

Key Features of Dermatomyositis

• Characterized by a distinctive skin rash
• Muscle weakness, particularly in the proximal muscles
• Elevated muscle enzymes, such as creatine kinase
• Electromyography and muscle biopsy to confirm diagnosis Treatment usually begins with high-dose corticosteroids (prednisone 1 mg/kg/day) for several weeks, followed by a gradual taper, as recommended by 1. Steroid-sparing agents such as methotrexate (15-25 mg weekly), azathioprine (2-3 mg/kg/day), or mycophenolate mofetil (1-1.5 g twice daily) are often added for long-term management, as suggested by 1. Physical therapy is essential to maintain muscle strength and prevent contractures. The disease affects women more frequently than men and typically develops between ages 40-60. Early diagnosis and treatment are crucial to prevent irreversible muscle damage and improve long-term outcomes.

Treatment Approach

• High-dose corticosteroids as initial treatment
• Steroid-sparing agents for long-term management
• Physical therapy to maintain muscle strength and prevent contractures
• Early diagnosis and treatment to prevent irreversible muscle damage and improve long-term outcomes.

From the Research

Inflammatory Myopathies in Adults

• The most common inflammatory myopathies in adults include dermatomyositis, polymyositis, and inclusion body myositis 2, 3, 4, 5.
• Inclusion body myositis is recognized as the most common myopathy presenting in patients over the age of 50 years 4.
• The diagnosis of inflammatory myopathies is based on the finding of weakness on exam, elevated muscle enzymes, characteristic histopathology of muscle biopsies, electromyography abnormalities, and rash in dermatomyositis 5.

Characteristics of Inflammatory Myopathies

• Dermatomyositis and polymyositis are clearly inflammatory, both clinically and histologically, and generally respond to therapy directed towards inflammation 4.
• Inclusion body myositis responds only modestly and sometimes not at all to immunosuppressive therapy 4.
• Myositis-specific antibodies have been helpful in defining subsets of patients with different responses to treatment and prognosis 5.

Treatment of Inflammatory Myopathies

• The cornerstone of therapy is corticosteroids with the addition of other immunosuppressives in severe or refractory disease or patients with intolerable side effects 2, 3, 5.
• Intravenous immunoglobulin, rituximab, and tacrolimus may offer additional benefit in the treatment of inflammatory myopathies 2, 3.