Is MRI with or without contrast recommended for diagnosing myositis?

MRI for Myositis: Contrast Recommendation

For suspected myositis, MRI without contrast is sufficient for initial diagnosis, with contrast reserved for specific clinical scenarios including suspected abscess, necrosis, vascular complications, or when initial non-contrast findings are equivocal. 1

Initial Imaging Approach

Both contrast-enhanced and non-contrast MRI are considered equivalent alternatives for diagnosing musculoskeletal inflammatory conditions, including myositis. 1 The American College of Radiology explicitly states these modalities have equal appropriateness ratings for initial evaluation. 1

Optimal MRI Protocol

• T2-weighted and STIR (Short Tau Inversion Recovery) sequences are the preferred protocols for detecting muscle inflammation, as they enhance visualization of edema and inflammatory changes characteristic of myositis. 1
• Non-contrast MRI effectively identifies muscle edema patterns that distinguish active inflammation from chronic damage (atrophy/fat replacement). 2
• MRI can detect muscle inflammation even when clinical signs are absent, making it highly sensitive for early disease. 1

When to Add Contrast

Reserve contrast administration for the following specific scenarios: 1

• Suspected abscess or necrosis - Contrast helps delineate areas of tissue destruction and fluid collections requiring drainage 1
• Vascular complications - When assessing muscle perfusion patterns or vascular involvement 1
• Equivocal non-contrast findings - When initial imaging does not provide diagnostic clarity 1
• Guiding biopsy site selection - Particularly in atypical presentations where tissue diagnosis is needed 1

Integration with Other Diagnostic Tools

MRI should never serve as the sole diagnostic tool for myositis. 1 A comprehensive diagnostic approach includes:

• Clinical examination findings (muscle weakness is more typical than pain) 3
• Laboratory values: creatine kinase (CK), aldolase, inflammatory markers (ESR, CRP), troponin for cardiac involvement 3
• Electromyography (EMG) when diagnosis is uncertain or neurologic overlap suspected 3
• Muscle biopsy for definitive diagnosis, especially in atypical presentations 1
• Autoantibody testing for myositis-specific antibodies 3

Monitoring Disease Activity

MRI is highly effective for serial monitoring of treatment response and disease activity over time. 1 Non-contrast sequences remain adequate for follow-up imaging, as they can:

• Distinguish active inflammation (edema on T2/STIR) from chronic damage (fat replacement) 2
• Guide therapy adjustments by determining whether weakness relates to active inflammation or irreversible damage 2
• Assess response to immunosuppressive treatment 1

Common Pitfalls to Avoid

• Do not delay treatment for MRI - In acute presentations with high clinical suspicion, empiric treatment should not be postponed for imaging 3
• Avoid misinterpreting myositis mimics - Many conditions (muscular dystrophies, denervation, diabetic myonecrosis, deep venous thrombosis, muscle injury) can produce similar MRI findings 4
• Ensure expert interpretation - MRI should be interpreted by a radiologist experienced in musculoskeletal imaging to accurately assess inflammatory changes 1
• Consider corticosteroid effects - Prior corticosteroid treatment may abolish inflammatory infiltrations on biopsy despite persistent MRI abnormalities 5

Practical Implementation Algorithm

1. Start with non-contrast MRI using T2-weighted/STIR sequences for all suspected myositis cases 1
2. Add contrast only if:
   • Infectious myositis suspected (abscess/necrosis concern) 1
   • Vascular assessment needed 1
   • Initial findings inconclusive 1
3. Integrate MRI findings with CK, aldolase, EMG, and clinical examination 3, 1
4. Use MRI to target biopsy sites when tissue diagnosis required 1
5. Employ non-contrast MRI for treatment monitoring 1, 2