What is the initial treatment for a patient diagnosed with myositis?

Initial Treatment for Myositis

The initial treatment for patients diagnosed with myositis should be high-dose corticosteroids (prednisone 0.5-1 mg/kg/day) with concurrent initiation of a steroid-sparing agent such as methotrexate, azathioprine, or mycophenolate mofetil. 1

Treatment Algorithm Based on Disease Severity

Mild Myositis (Grade 1)

• Muscle weakness with or without pain
• Treatment:
  • Prednisone 0.5 mg/kg/day if CK/aldolase elevated and muscle weakness present 2
  • Acetaminophen or NSAIDs for myalgia if no contraindications 2
  • Consider holding statins if patient is taking them 2
  • Monitor CK, ESR, and CRP levels regularly 2

Moderate Myositis (Grade 2)

• Moderate weakness with or without pain limiting instrumental activities of daily living
• Treatment:
  • Prednisone 0.5-1 mg/kg/day 2
  • Initiate steroid-sparing agent concurrently (methotrexate, azathioprine, or mycophenolate mofetil) 1
  • NSAIDs as needed for pain management 2
  • Referral to rheumatologist or neurologist 2
  • Complete autoimmune myositis blood panel, EMG, MRI of affected joints 2

Severe Myositis (Grade 3-4)

• Severe weakness limiting self-care activities of daily living
• Treatment:
  • Consider hospitalization, especially with respiratory compromise, dysphagia, or rhabdomyolysis 2
  • Initiate prednisone 1 mg/kg/day orally or methylprednisolone 1-2 mg/kg IV (or higher dose bolus for severe cases) 2
  • Urgent referral to rheumatologist and/or neurologist 2
  • Consider additional therapies for severe or refractory disease:
    • Plasmapheresis for acute or severe disease 2
    • IVIG therapy (note: slower onset of action) 2, 1
    • Other immunosuppressants including biologics (rituximab), TNFα or IL-6 antagonists 2

Key Diagnostic Considerations

• Complete rheumatologic and neurologic examination including muscle strength testing 2
• Blood tests: CK, aldolase, transaminases (AST, ALT), LDH, inflammatory markers (ESR, CRP) 2
• Cardiac evaluation: troponin, ECG, echocardiogram or cardiac MRI if myocardial involvement suspected 2
• Consider EMG, MRI, and/or muscle biopsy when diagnosis is uncertain 2
• Autoantibody testing to evaluate for myositis-specific antibodies and rule out overlap syndromes 2

Important Considerations and Pitfalls

• Myositis with myocardial involvement has high mortality and requires aggressive treatment 1
• Plasmapheresis should not be performed immediately after IVIG as it will remove immunoglobulin 2
• Early recognition and treatment is critical to prevent permanent muscle damage 1
• Steroid-sparing agents should be initiated early to minimize corticosteroid-related complications 1
• Distinguish true inflammatory myositis from other causes of muscle weakness:
  • Polymyalgia rheumatica (normal CK, pain without true weakness) 2
  • Drug-induced myopathies (especially statins) 2
  • Neuromuscular junction disorders 2
  • Metabolic myopathies 2

Monitoring Response to Treatment

• Regular assessment of muscle strength and function
• Monitor CK levels to assess treatment response
• Taper corticosteroids gradually based on clinical improvement and normalization of CK levels
• Continue steroid-sparing agents to maintain remission and minimize steroid exposure

The treatment approach should be adjusted based on clinical response, with escalation of therapy for refractory cases and careful tapering of corticosteroids to minimize side effects while maintaining disease control.