Idiopathic inflammatory myopathies: a review

Area of Science:

• Neurology
• Rheumatology
• Immunology

Background:

• Idiopathic inflammatory myopathy (IIM) encompasses several subtypes, including dermatomyositis (DM), overlap myositis (OM), and necrotising autoimmune myopathy (NAM).
• Polymyositis (PM) is debated as a distinct entity, potentially overlapping with OM and NAM.
• Immune-mediated necrotising myopathy (IMNAM) is a recognized subtype of IIM.

Purpose of the Study:

• To provide a diagnostic algorithm for distinguishing between IIM subtypes.
• To emphasize the roles of clinical assessment, serology, and imaging in IIM diagnosis.
• To discuss current and evolving therapeutic options for IIM, including immunotherapy.

Main Methods:

• Review of clinical presentations, serological markers, and imaging techniques for IIM diagnosis.
• Development of a diagnostic algorithm to differentiate IIM subtypes.
• Analysis of therapeutic strategies, including intravenous immunoglobulin and rituximab for refractory cases.

Main Results:

• DM, OM, and NAM typically present with proximal muscle weakness and elevated creatine kinase (CK) levels.
• Sporadic inclusion body myositis (IBM) characteristically affects finger flexors and quadriceps, often with normal or mildly elevated CK.
• Advancements in serology and imaging are reducing reliance on muscle biopsy for diagnosis.

Conclusions:

• A diagnostic approach integrating clinical evaluation, serology, and imaging is crucial for accurate IIM subtyping.
• Intravenous immunoglobulin and rituximab show promise in managing refractory IIM.
• The diagnostic and therapeutic landscape for IIM is continuously evolving.