Causes of Inflammatory Myositis in Elderly
The main causes of inflammatory myositis in the elderly include immune-mediated necrotizing myopathy triggered by medications (particularly statins), viral infections, malignancies, and immune checkpoint inhibitor therapy. 1
Primary Types of Inflammatory Myopathies in the Elderly
Dermatomyositis (DM): Characterized by symmetric proximal muscle weakness, elevated muscle enzymes, and distinctive skin manifestations (heliotrope rash, Gottron papules, periungual telangiectasias) 1
Polymyositis (PM): Features symmetric proximal muscle weakness with CD8+ cytotoxic T cells invading non-necrotic muscle fibers 1
Immune-Mediated Necrotizing Myopathy (IMNM): Presents with severe proximal muscle weakness, markedly elevated creatine kinase (CK) levels (>10 times normal), and minimal inflammatory infiltrate on muscle biopsy 1
Sporadic Inclusion Body Myositis (sIBM): Shows degenerative features with muscle fiber vacuolization and abnormal accumulation of amyloid-β and phosphorylated tau proteins 1
Specific Causes and Triggers
Medication-Induced Myositis
Statins: Major trigger for immune-mediated necrotizing myopathy, associated with antibodies against 3-hydroxy-3-methylglutaryl-coenzyme A (HMGCR) protein 1
Immune Checkpoint Inhibitors (ICPIs): Can cause severe and potentially fatal myositis, more common with anti-PD-1/PD-L1 than with anti-CTLA-4 agents 1
- May present as reactivation of pre-existing paraneoplastic polymyositis/dermatomyositis or as de novo myositis
- Can have a fulminant necrotizing course with rhabdomyolysis and myocardial involvement
Infectious Causes
Viral infections: Including influenza, HIV, and SARS-CoV2 can trigger inflammatory myopathies 2
Bacterial infections: May serve as environmental triggers for myositis development 3
Malignancy-Associated Myositis
- Paraneoplastic syndrome: Particularly associated with dermatomyositis in elderly patients 2
- Requires thorough cancer screening, especially in newly diagnosed cases
Autoimmune Conditions
Overlap syndromes: Inflammatory myositis can occur in conjunction with other autoimmune disorders such as rheumatoid arthritis 4, 5
Antisynthetase syndrome: Characterized by myositis, interstitial lung disease, arthritis, Raynaud's phenomenon, and mechanic's hands 5
Diagnostic Considerations
Laboratory evaluation: Check muscle enzymes (CK, aldolase), inflammatory markers (ESR, CRP), and myositis-specific autoantibodies 1
Imaging: MRI with T1-weighted, T2-weighted, and fat suppression techniques can identify muscle inflammation and guide biopsy site selection 1
Electromyography (EMG): May show polyphasic motor unit action potentials of short duration and low amplitude with increased insertional and spontaneous activity 1
Muscle biopsy: Essential for definitive diagnosis and classification of myositis subtype 1
Clinical Pearls and Pitfalls
Age-specific considerations: Elderly patients with inflammatory myositis have higher risk of malignancy and statin exposure 1
Differential diagnosis: Important to distinguish inflammatory myositis from polymyalgia rheumatica, which presents with pain but not true weakness and normal CK levels 1
Comorbidity impact: Elderly patients often have comorbidities that can complicate diagnosis and treatment (cardiovascular disease, osteoporosis, diabetes) 1
Treatment challenges: Elderly patients may have increased risk of immunosuppressive therapy complications and require careful monitoring 1
Prognosis factors: Advanced age, presence of dysphagia, cardiac involvement, and associated malignancy are associated with poorer outcomes 1