What is the treatment for polymyositis?

Treatment of Polymyositis

The first-line treatment for polymyositis is high-dose corticosteroids (prednisone) initiated concurrently with a steroid-sparing agent such as methotrexate, azathioprine, or mycophenolate mofetil, followed by a gradual tapering course of corticosteroids. 1

Initial Treatment Approach

Corticosteroid Therapy

• Begin with high-dose prednisone:
  • Adults: 1 mg/kg/day (up to 60-80 mg daily) 1
  • Continue high-dose daily treatment for the first month
  • After the first month, transition to alternate-day dosing 2
  • Taper gradually and slowly over months based on clinical response and muscle enzyme levels

Steroid-Sparing Agents (start concurrently with steroids)

• First-line options:
  • Methotrexate: 15-25 mg weekly
  • Azathioprine: 2-3 mg/kg/day
  • Mycophenolate mofetil: 2-3 g/day 1

Treatment for Severe or Refractory Disease

For patients with severe myositis, extensive extramuscular involvement, or disease refractory to initial therapy:

• High-dose intravenous methylprednisolone (1000 mg daily for 3-5 days) 1
• Additional therapies to consider:
  • Intravenous immunoglobulin (IVIG): Particularly effective in steroid-resistant cases 3
  • Cyclophosphamide: For severe disease with interstitial lung disease
  • Rituximab: For refractory cases
  • Cyclosporine: Alternative for refractory disease 1

Monitoring Treatment Response

• Assess muscle strength regularly using standardized measures
• Monitor creatine kinase (CK) levels and other muscle enzymes
• Evaluate functional improvement in activities of daily living
• Magnetic resonance imaging (MRI) can help monitor muscle inflammation and treatment response 1

Duration of Treatment

• Long-term therapy is typically required
• Average treatment duration is approximately 27 months 2
• Maintenance therapy may be needed for several years in many patients 4
• Approximately one-third of patients may have residual muscle weakness despite treatment 4

Managing Corticosteroid Side Effects

• Implement bone health monitoring with dual-energy x-ray absorptiometry
• Prescribe calcium and vitamin D supplements
• Consider bisphosphonate therapy if osteoporosis develops
• Use Pneumocystis prophylaxis (e.g., trimethoprim-sulfamethoxazole) when prednisone dose is ≥20 mg daily for ≥4 weeks 1
• Monitor for weight gain, hypertension, hyperglycemia, and other steroid-related complications

Prognosis

• 5-year survival rate for treated patients is approximately 95% 4
• Treatment response is better in patients who:
  • Are younger
  • Do not have associated malignancy or cardiac disease
  • Begin treatment within 24 months of symptom onset 2
  • Receive adequate initial corticosteroid dosing

Important Considerations

• Distinguish polymyositis from other inflammatory myopathies (dermatomyositis, inclusion body myositis, immune-mediated necrotizing myopathy) as treatment response varies 5
• Screen for malignancy, especially in older patients or those with treatment resistance
• Evaluate for interstitial lung disease, cardiac involvement, and dysphagia which may require additional targeted therapies
• Consider myositis-specific autoantibodies to help guide prognosis and treatment approach 1