What is the initial treatment for myositis management?

Initial Treatment for Myositis

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

Diagnostic Evaluation Before Treatment

• A comprehensive rheumatologic and neurologic examination, including muscle strength testing, is essential before initiating treatment 1
• Laboratory evaluation should include:
  • Muscle enzymes: CK, transaminases, LDH, and aldolase 1
  • Inflammatory markers: ESR and CRP 1
  • Autoimmune tests as required for differential diagnosis 2
• Cardiac evaluation with troponin and echocardiogram should be considered if myocardial involvement is suspected 1
• Consider EMG (electromyography) and/or MRI to show muscle fibrillations or increased intensity and edema in affected muscles 2

Treatment Algorithm

First-Line Therapy

• Initiate prednisone at 0.5-1 mg/kg per day (typically 60-80 mg daily) 1
• Simultaneously start a steroid-sparing agent to improve outcomes and reduce steroid-related side effects 1:
  • Methotrexate (15-20 mg/m²/week, preferably subcutaneous) 1, 3
  • Azathioprine 1, 3
  • Mycophenolate mofetil 1, 3

Treatment Based on Disease Severity

Mild to Moderate Disease

• Continue prednisone with gradual tapering as symptoms improve 2, 1
• Monitor response through clinical assessment and laboratory markers 1

Severe Disease

• Consider methylprednisolone pulse therapy (high-dose IV) 1, 3
• Additional therapies to consider:
  • Intravenous immunoglobulin (IVIG) 2, 3
  • Cyclophosphamide (500-1000 mg/m² IV monthly) 3
  • Cyclosporine 3
  • Rituximab for refractory cases 3

For Immune Checkpoint Inhibitor-Related Myositis

• Grade 2 toxicity: Hold immune checkpoint inhibitor therapy and resume upon symptom control 1
• Grade 3-4 toxicity: Hold therapy and potentially resume in consultation with rheumatology 2
• If any evidence of myocardial involvement, permanently discontinue immune checkpoint inhibitor therapy 2

Monitoring and Follow-up

• Regular assessment of muscle strength using validated measures 3
• Monitor 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
• Begin tapering prednisone dose as clinical improvement is observed 3
• Continue steroid-sparing agent for at least one year after achieving remission 3

Common Pitfalls and Considerations

• Failure to screen for malignancy in adult patients, especially with dermatomyositis 1
• Inadequate initial dosing of corticosteroids 1
• Delaying initiation of steroid-sparing agents 1
• Not considering cardiac involvement, which can be life-threatening 2
• TNF-α antagonists should be avoided as they may exacerbate interstitial lung disease and myositis 4
• Caution is advised when rechallenging patients with immune checkpoint inhibitors after myositis 2

Special Populations

• For patients with refractory disease, consider:
  • Switching to alternative DMARDs if intolerant to methotrexate 3
  • IVIG, which is particularly effective for skin manifestations 3
  • Rituximab, though effects may take up to 26 weeks to appear 3, 5