- Epidemiology
- Etiology involves both autoimmune (CD8+ T-cells) and degenerative processes (protein accumulation).
- Clinical Presentation
- Insidious onset; Asymmetric weakness.
- Distal: Finger flexors (weak grip), foot dorsiflexors.
- Proximal: Quadriceps (knee buckling/falls).
- Dysphagia.
- Diagnostics
- Labs: Normal or Mild ↑ CK; Anti-cN1A positive.
- Pathology (Muscle Biopsy)
- Definitive diagnosis requires biopsy.
- Endomysial inflammation with CD8+ T-cell infiltration (similar to Polymyositis).
- Rimmed Vacuoles: Basophilic inclusions with granular rims in muscle fibers (Hallmark).
- Intracellular inclusions containing β-amyloid and tau protein (seen on EM).
- Management
- Refractory to steroids and immunosuppression (Suspect IBM if “Polymyositis” fails Tx).
- Supportive care only.