What is the initial treatment for myositis?

Initial Treatment for Myositis

The initial treatment for inflammatory myositis should begin with high-dose corticosteroids (0.5-1 mg/kg/day, typically 60-80 mg/day of prednisone) concurrent with a steroid-sparing agent such as methotrexate, azathioprine, or mycophenolate mofetil. 1

Diagnostic Evaluation

• Complete rheumatologic and neurologic examination, including muscle strength testing, is essential before initiating treatment 2
• Laboratory evaluation should include:
  • Muscle enzymes: CK, transaminases (AST, ALT), LDH, and aldolase 2
  • Inflammatory markers: ESR and CRP 2
  • Cardiac evaluation with troponin and echocardiogram if myocardial involvement is suspected 2
• Consider EMG, MRI, and/or muscle biopsy when diagnosis is uncertain or overlap with other conditions is suspected 2

Treatment Algorithm

Initial Therapy

• Begin prednisone at 0.5-1 mg/kg per day (typically 60-80 mg daily as a single dose) 1
• Concurrently initiate a steroid-sparing immunosuppressive agent to improve outcomes and reduce steroid-related side effects 1
• Options include:
  • Methotrexate
  • Azathioprine
  • Mycophenolate mofetil 1

Corticosteroid Tapering

• Begin tapering corticosteroids after 2-4 weeks depending on patient response 1
• Follow a structured tapering schedule:
  • Reduce by 10 mg every 2 weeks until reaching 30 mg/day
  • Then by 5 mg every 2 weeks until reaching 20 mg/day
  • Finally by 2.5 mg every 2 weeks 1
• Important: Continue the initial corticosteroid dose until the serum CK has normalized before beginning the taper 3
• A rising CK, even within the normal range, may signal an impending clinical relapse 3

Severity-Based Treatment Modifications

For Mild Disease (Grade 1)

• NSAIDs and acetaminophen may be sufficient for analgesia 2
• If CK is elevated with muscle weakness, initiate oral corticosteroids 2

For Moderate Disease (Grade 2)

• Prednisone 10-20 mg/day for 4-6 weeks 2
• If no improvement after initial 4-6 weeks, treat as severe disease 2
• Consider referral to rheumatology 2

For Severe Disease (Grade 3-4)

• Prednisone 0.5-1 mg/kg/day 2
• Consider high-dose methylprednisolone pulse therapy (10-20 mg/kg or 250-1000 mg for 1-5 consecutive days) 1
• Additional therapies to consider:
  • Cyclophosphamide
  • Cyclosporine
  • Intravenous immunoglobulin (IVIG) 1
• Urgent referral to rheumatology or neurology 2

Special Considerations

Juvenile Dermatomyositis

• Begin corticosteroids at 2 mg/kg up to a maximum of 60 mg/day 1
• Add subcutaneous methotrexate at treatment onset (15 mg/m² once weekly) 1

Immune-Mediated Necrotizing Myopathy

• May require more aggressive therapy due to potentially severe weakness 1
• Treatment approach similar to dermatomyositis/polymyositis with corticosteroids and immunosuppressants 1

Immune Checkpoint Inhibitor-Related Myositis

• For grade 2 toxicity: Hold immune checkpoint inhibitor therapy and resume upon symptom control 2
• For grade 3-4 toxicity: Hold immune checkpoint inhibitor and may resume in consultation with rheumatology if recovery to grade 1 or less 2
• Approximately 10% of patients may require intravenous methylprednisolone pulses 1

Monitoring and Follow-up

• Regular monitoring of muscle enzyme levels (CK) and inflammatory markers (ESR, CRP) 1
• MRI with T1-weighted, T2-weighted, and fat suppression techniques can help monitor treatment response 1
• Achievement of a CK within the low normal range predicts a prolonged biochemical remission 3

Common Pitfalls

• Failure to screen for malignancy in adult patients, especially with dermatomyositis 1
• Inadequate initial dosing of corticosteroids 1
• Tapering corticosteroids too quickly or before CK normalizes 3
• Delaying initiation of steroid-sparing agents 1
• Failure to combine pharmacological treatment with individualized and supervised exercise 4

Exercise Therapy

• Combining immunosuppressive treatment with individualized and supervised exercise is recommended to improve muscle performance and reduce disease activity 4