What is the term for inflammatory muscle disease?

Myositis: The Term for Inflammatory Muscle Disease

Myositis is the medical term for inflammatory muscle disease, with the broader classification being idiopathic inflammatory myopathies (IIM). 1

Understanding Myositis (IIM)

Idiopathic inflammatory myopathies (IIM), collectively known as myositis, represent a group of rare, systemic autoimmune diseases that primarily affect skeletal muscles, resulting in:

• Proximal muscle weakness
• Elevated muscle enzyme levels
• Various extramuscular manifestations (fever, weight loss, rash)

Major Subgroups of Myositis

The IIM classification includes several distinct subgroups:

1. Dermatomyositis (DM):

   • Characterized by muscle inflammation plus distinctive skin manifestations
   • Features include heliotrope rash, Gottron papules, periorbital edema, and periungual telangiectasias
   • Occurs in both children (juvenile DM) and adults 1

2. Polymyositis (PM):

   • Characterized by symmetric proximal muscle weakness
   • Distinct immunopathology with CD8+ cytotoxic T cells invading non-necrotic muscle fibers 1

3. Inclusion Body Myositis (IBM):

   • Features degenerative neuromuscular characteristics
   • Muscle fiber vacuolization with abnormal accumulation of amyloid-β and phosphorylated tau proteins
   • Generally resistant to immunosuppressive therapy 1

4. Immune-Mediated Necrotizing Myopathy (IMNM):

   • Severe myopathy with minimal inflammatory infiltrate on muscle biopsy
   • May be triggered by viral infections, medications (particularly statins), or malignancies 1

5. Juvenile Dermatomyositis (JDM):

   • Affects children under 18 years
   • Characterized by proximal muscle weakness, calcinosis cutis, cutaneous vasculitis, and ulcerations 1

Clinical Significance and Management

Myositis requires careful diagnostic evaluation including:

• Muscle enzyme assessment
• Myositis-specific autoantibody testing
• Magnetic resonance imaging
• Muscle biopsy
• Electromyography

Important Clinical Considerations

1. Cancer Screening:

   • Up to 25% of adult IIM patients develop cancer within 3 years of diagnosis
   • Cancer is the leading cause of death in adults with IIM
   • Early detection is critical as most IIM-associated cancers are diagnosed at advanced stages 1

2. Treatment Approach:

   • Most forms (except IBM) respond to immunosuppressive therapy
   • First-line treatment typically includes high-dose corticosteroids with a steroid-sparing agent
   • For refractory cases, additional therapies like IVIG, rituximab, or cyclophosphamide may be considered 1

Recent Advances

Recent research has identified:

• Myositis-specific autoantibodies that define patient subgroups and offer prognostic implications
• Novel biomarkers of disease activity (IL-6, type 1 interferon-regulated genes)
• Improved imaging techniques for assessment and monitoring 1

The classification and understanding of myositis continue to evolve as new research emerges, with implications for both diagnosis and treatment approaches.