Treatment of Acute Necrotizing Myositis

Diagnosis and Treatment

• The immediate priority is determining whether this is infectious necrotizing myositis or immune-mediated necrotizing myopathy, as the treatments are fundamentally different and delay in either scenario increases mortality, according to the Infectious Diseases Society of America 1, 2
• Urgent surgical exploration and complete debridement of necrotic muscle tissue must be performed immediately in cases of infectious necrotizing myositis, as this is the cornerstone of treatment and delays significantly increase mortality, with a reported 36.5% mortality rate even with treatment, as stated by the Infectious Diseases Society of America 1
• Obtain immediate surgical consultation, as this is a life-threatening emergency with 36.5% mortality rate even with treatment, and obtain blood cultures and tissue cultures from affected muscle, as recommended by the Infectious Diseases Society of America 1
• Start broad-spectrum empiric antibiotics immediately covering both aerobic and anaerobic organisms, including vancomycin 15 mg/kg IV every 12 hours and piperacillin-tazobactam 4.5 g IV every 8 hours, as suggested by the Infectious Diseases Society of America 1
• Once Group A Streptococcus is confirmed, switch to penicillin plus clindamycin, as clindamycin inhibits toxin production which is critical in streptococcal necrotizing infections, according to the Infectious Diseases Society of America 1
• Initiate high-dose corticosteroids immediately, such as prednisone 1 mg/kg/day or 60-80 mg/day, concurrently with a steroid-sparing agent, in cases of immune-mediated necrotizing myopathy, as recommended by the American College of Rheumatology 3, 2
• Administer IV methylprednisolone pulse therapy 10-20 mg/kg for 1-5 consecutive days in addition to other immunosuppressive agents, for severe disease or extensive involvement, as suggested by the American College of Rheumatology 3, 2

Monitoring and Management

• Serial creatine kinase levels and inflammatory markers, such as ESR and CRP, are essential to guide treatment response, as stated by the American College of Rheumatology 2
• Muscle strength assessment at each visit and MRI with T1, T2, and fat suppression sequences to monitor treatment response, are recommended by the American College of Rheumatology 2, 3
• For infectious cases, repeat imaging if persistent bacteremia to identify undrained collections, as suggested by the Infectious Diseases Society of America 1

Special Considerations

• If the patient has recent checkpoint inhibitor exposure, immediately discontinue the agent and treat aggressively with high-dose corticosteroids plus IVIG, as checkpoint inhibitor-induced necrotizing myositis has particularly high mortality, according to the American College of Rheumatology 2
• Patients with concomitant myocarditis and/or myasthenia gravis have particularly poor prognosis with high mortality rates, as stated by the American College of Rheumatology 2
• Screen for underlying malignancy in adult patients with immune-mediated disease, especially dermatomyositis, as recommended by the American College of Rheumatology 3