Treatment of Inflammatory Necrotizing Myositis

Initial Management

High-dose corticosteroids, typically prednisone 1 mg/kg/day orally or methylprednisolone IV for severe cases, should be started immediately upon diagnosis, as recommended by the American College of Rheumatology, with a steroid-sparing agent initiated concurrently to allow for eventual steroid tapering 1, 2
Options for steroid-sparing agents include methotrexate (15-25 mg weekly), azathioprine (2-3 mg/kg/day), and mycophenolate mofetil (2-3 g/day), as suggested by the Mayo Clinic Proceedings 2

For patients with severe disease, extensive extramuscular involvement, or inadequate response to initial therapy, intravenous immunoglobulin (IVIG) at 2 g/kg divided over 2-5 days may be considered, as recommended by the Journal of Clinical Oncology 1
Plasmapheresis should be considered in cases with poor response to corticosteroids or in life-threatening situations, according to the Journal of Clinical Oncology 1
Cyclophosphamide or cyclosporine may be considered for severe or refractory cases, as suggested by the Mayo Clinic Proceedings 2

If myositis is immune checkpoint inhibitor (ICPi)-induced, discontinuation of the offending agent is essential, and high-dose corticosteroids with IVIG may be required, as recommended by the Journal of Clinical Oncology 1, 3
For necrotizing myositis with infectious etiology, appropriate broad-spectrum antibiotics covering both aerobic and anaerobic organisms should be administered, and surgical debridement may be necessary for infectious necrotizing fasciitis, as suggested by the Clinical Infectious Diseases journal 4

Serial measurements of muscle enzymes (especially creatine kinase) and inflammatory markers should be performed, as recommended by the Journal of Clinical Oncology and the Mayo Clinic Proceedings 1, 2
Regular assessment of muscle strength and function is necessary, according to the Mayo Clinic Proceedings 2
MRI can be useful to monitor treatment response, as suggested by the Mayo Clinic Proceedings 2
Patients with concomitant myocarditis and/or myasthenia gravis have a particularly poor prognosis with high mortality rates, as reported by the Journal of Clinical Oncology 1