What is the treatment for polymyositis?

Treatment of Polymyositis

The cornerstone of initial treatment for polymyositis is high-dose corticosteroids (prednisone 1 mg/kg/day up to 60 mg/day) administered concurrently with a steroid-sparing agent such as methotrexate, azathioprine, or mycophenolate mofetil, followed by a tapering course of corticosteroids. 1, 2

Diagnostic Criteria

Before initiating treatment, confirm the diagnosis with:

• Symmetric proximal muscle weakness (primarily in upper and lower extremities)
• Elevated muscle enzymes (CK, LDH, AST, ALT)
• Abnormal EMG showing myopathic changes
• Muscle biopsy showing inflammatory infiltrates with CD8+ T cells invading non-necrotic muscle fibers
• Absence of skin rash (to differentiate from dermatomyositis)

Treatment Algorithm

First-Line Therapy

1. High-dose corticosteroids:

   • Prednisone 1 mg/kg/day orally (maximum 60 mg/day) 1, 2
   • For severe cases: IV methylprednisolone pulse therapy (1g/day for 3-5 days) 1

2. Concurrent steroid-sparing agent (start at the same time as corticosteroids):

   • Methotrexate: 15-25 mg weekly (preferred first choice) 1, 2, 3
   • Azathioprine: 2-3 mg/kg/day (alternative) 1, 4
   • Mycophenolate mofetil: 2-3 g/day (especially if lung involvement) 1, 2

3. Corticosteroid taper:

   • Begin taper after 2-4 weeks if clinical improvement and CK levels decrease
   • Slow taper over months (typically 10% reduction every 2-4 weeks)

For Severe or Refractory Disease

1. Intravenous immunoglobulin (IVIG):

   • 2 g/kg divided over 2-5 days 1, 2, 3
   • Particularly effective for patients with dysphagia or respiratory muscle involvement

2. Other options:

   • Rituximab (for refractory cases) 2, 4
   • Cyclophosphamide (for severe cases with organ involvement) 1, 2
   • Cyclosporine (particularly useful with lung involvement) 1, 2
   • Plasmapheresis (for life-threatening cases with poor response to corticosteroids) 1

Monitoring Treatment Response

• Assess muscle strength regularly using manual muscle testing
• Monitor CK levels every 4-6 weeks initially, then every 3 months
• Evaluate for extramuscular manifestations (cardiac, pulmonary, gastrointestinal)
• Follow inflammatory markers (ESR, CRP)

Special Considerations

Extramuscular Manifestations

• Pulmonary involvement: More aggressive immunosuppression may be needed; consider mycophenolate mofetil or cyclophosphamide 1
• Cardiac involvement: Requires cardiac monitoring and possibly specific cardiac treatment 1
• Dysphagia: May require IVIG and more aggressive therapy 3

Potential Pitfalls

1. Delayed diagnosis and treatment: Can lead to irreversible muscle damage and disability
2. Inadequate initial therapy: Starting with insufficient doses of corticosteroids or delaying steroid-sparing agents
3. Too rapid steroid taper: Can lead to disease flare
4. Overlooking malignancy: Always screen for underlying malignancy, particularly in older patients
5. Missing medication-induced myositis: Review all medications, particularly statins

Duration of Treatment

• Most patients require treatment for several years 5
• The 5-year survival rate for treated patients is approximately 95% 5
• Up to one-third of patients may be left with residual muscle weakness 5

Supportive Care

• Physical therapy is essential during the recovery phase to improve muscle strength and prevent contractures 3
• Prompt treatment of infections is critical as they can exacerbate disease and are a common cause of mortality 3
• Calcium and vitamin D supplementation to prevent corticosteroid-induced osteoporosis

Remember that early aggressive treatment is key to preventing irreversible muscle damage and improving long-term outcomes in patients with polymyositis.