Proximal Myositis: Definition and Treatment
Proximal myositis should be treated with corticosteroids as first-line therapy (prednisone 0.5-1 mg/kg/day), often combined with steroid-sparing agents, and severity-based management according to established grading systems. 1, 2
Definition and Clinical Presentation
Proximal myositis is an inflammatory muscle disorder characterized by:
- Inflammation of proximal muscles (shoulders, upper arms, hips, thighs)
- Muscle weakness, pain, and stiffness
- Elevated muscle enzymes (creatine kinase/CK)
- Abnormal electromyography (EMG) findings
- Possible abnormalities on muscle MRI or biopsy
It differs from non-inflammatory proximal myalgia, which presents with pain and stiffness but without true muscle inflammation, weakness, or elevated CK 1.
Diagnostic Evaluation
Laboratory Tests
- Muscle enzymes: CK, LDH, AST
- Inflammatory markers: ESR, CRP
- Autoimmune markers: ANA, RF, anti-CCP
- Myositis-specific antibodies
- Complete blood count and metabolic panel
- Thyroid function tests
- 25-OH vitamin D levels 2
Additional Testing
- EMG to assess for myopathic changes
- Muscle MRI to evaluate for inflammation
- Muscle biopsy (gold standard) to confirm diagnosis and determine subtype 2
Treatment Algorithm Based on Severity
Grade 1 (Mild)
- Mild weakness with or without pain
- Management:
- Continue immunotherapy if applicable
- Analgesics: acetaminophen or NSAIDs if no contraindications
- Monitor CK levels 1
Grade 2 (Moderate)
- Moderate weakness limiting instrumental activities of daily living
- Management:
- Hold immunotherapy temporarily if applicable
- Prednisone 0.5-1 mg/kg/day if CK is elevated
- Referral to rheumatologist or neurologist
- Consider permanent discontinuation of immunotherapy if objective findings present 1
Grade 3-4 (Severe)
- Severe weakness limiting self-care activities
- Management:
- Permanently discontinue immunotherapy if applicable
- Consider hospitalization for severe weakness
- Prednisone 1 mg/kg/day or IV methylprednisolone 1-2 mg/kg
- For severe cases (affecting mobility, cardiac, respiratory function, or causing dysphagia), consider higher-dose bolus steroids
- Consider plasmapheresis or IVIG therapy
- Referral to specialist (rheumatologist or neurologist) 1, 2
Steroid-Sparing Agents
For patients with inadequate response to steroids after 4-6 weeks or to minimize steroid exposure, add one of the following:
- Methotrexate: Start at 15 mg/week orally with 1 mg/day folic acid, targeting 25 mg/week within 3-6 months
- Azathioprine: 2 mg/kg of ideal body weight (after checking thiopurine methyltransferase level)
- Mycophenolate mofetil: Start at 500 mg twice daily, increase by 500 mg/week until reaching 1000 mg twice daily
- Rituximab: For refractory cases, especially with specific myositis antibodies 1, 2
Corticosteroid Tapering
After 2-4 weeks of initial therapy with clinical improvement:
- Reduce by 10 mg every 2 weeks until reaching 30 mg/day
- Then reduce by 5 mg every 2 weeks until reaching 20 mg/day
- Then reduce by 2.5 mg every 2 weeks until reaching 10 mg/day
- Below 10 mg/day, slow the taper to 1 mg every 2-4 weeks until completed 2
Monitoring and Follow-up
- Regular assessment of muscle strength
- Serial CK measurements (target low-normal range)
- Functional status improvement
- Ability to taper corticosteroids
- Annual assessment of disease damage using validated indices 2
Potential Complications
- Steroid myopathy: Presents with insidious onset, minimal pain, normal or minimally elevated muscle enzymes, and worsens with continued high-dose therapy
- Cardiac complications: Including conduction defects and arrhythmias
- Respiratory complications: Can be life-threatening
- Dysphagia: May lead to aspiration pneumonia 2, 3
Exercise and Rehabilitation
- Combining pharmacological treatment with individualized and supervised exercise is recommended to improve muscle performance
- A structured rehabilitation program should be implemented, particularly for patients with steroid myopathy 2, 4
Important Considerations
- Early initiation of steroid-sparing agents can reduce steroid-related side effects
- Subgrouping patients into clinical and serological subtypes may help identify biomarkers for treatment response
- For refractory cases, consider combination therapy with tacrolimus, high-dose glucocorticoids, and IVIG 2, 4, 5