What is the treatment for inflammatory necrotizing myositis?

Treatment of Inflammatory Necrotizing Myositis

The cornerstone of treatment for inflammatory necrotizing myositis is high-dose corticosteroids, which should be administered as a bolus in severe cases, combined with a steroid-sparing agent such as methotrexate, azathioprine, or mycophenolate mofetil. 1

Initial Management

• Prompt initiation of aggressive immunosuppression is critical as necrotizing myositis can progress rapidly and cause irreversible muscle damage 2
• High-dose corticosteroids (typically prednisone 1 mg/kg/day orally or methylprednisolone IV for severe cases) should be started immediately upon diagnosis 1
• A steroid-sparing agent should be initiated concurrently with corticosteroids to allow for eventual steroid tapering 1
• Options include:
  • Methotrexate (15-25 mg weekly) 1
  • Azathioprine (2-3 mg/kg/day) 1
  • Mycophenolate mofetil (2-3 g/day) 1

Severe or Refractory Disease Management

• For patients with severe disease, extensive extramuscular involvement, or inadequate response to initial therapy: 1
• Intravenous immunoglobulin (IVIG) at 2 g/kg divided over 2-5 days 1, 2
• Plasmapheresis should be considered in cases with poor response to corticosteroids or in life-threatening situations 1
• Rituximab may be particularly effective for certain subtypes of necrotizing myositis, especially anti-SRP positive cases 2
• Cyclophosphamide or cyclosporine may be considered for severe or refractory cases 1

Treatment Based on Autoantibody Status

• Anti-HMGCR positive necrotizing myositis:
  • IVIG is particularly effective and may be sufficient as monotherapy in some cases 2
  • Statin discontinuation is essential if statin-associated 1, 3
• Anti-SRP positive necrotizing myositis:
  • Early rituximab is often recommended 2
  • More aggressive combination therapy may be required 2
• Antibody-negative necrotizing myositis:
  • Standard approach with corticosteroids and immunosuppressants 2

Special Considerations

• If myositis is immune checkpoint inhibitor (ICPi)-induced:
  • Discontinue the offending agent 1
  • High-dose corticosteroids with IVIG may be required 4
  • Monitor for potential cardiac involvement, which requires urgent treatment 1
• For necrotizing myositis with infectious etiology:
  • Appropriate broad-spectrum antibiotics covering both aerobic and anaerobic organisms 1
  • Surgical debridement may be necessary for infectious necrotizing fasciitis 1

Monitoring and Follow-up

• Serial measurements of muscle enzymes (especially creatine kinase) and inflammatory markers 1
• Regular assessment of muscle strength and function 1
• MRI can be useful to monitor treatment response 1
• Patients often require prolonged immunosuppression with careful tapering to prevent relapse 2

Common Pitfalls and Caveats

• Delay in diagnosis and treatment can lead to irreversible muscle damage and poor outcomes 2
• Young age of onset is associated with poorer prognosis 2
• Relapse is common when tapering immunosuppression, requiring close monitoring 2
• Patients with concomitant myocarditis and/or myasthenia gravis have a particularly poor prognosis with high mortality rates 1
• Conventional immunosuppression may be insufficient in some cases, necessitating novel approaches targeting B-cell depletion or antibody clearance 5