What is the initial treatment for myositis?

Initial Treatment for Myositis

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

Diagnostic Workup Before Treatment

• Complete rheumatologic and neurologic examination including muscle strength testing is essential before initiating treatment 2
• Laboratory evaluation should include:
  • Muscle enzymes: CK, aldolase, transaminases (AST, ALT), LDH 2
  • Inflammatory markers: ESR and CRP 2
  • Troponin to evaluate myocardial involvement 2
• Consider EMG, MRI, and/or muscle biopsy when diagnosis is uncertain 2
• Autoantibody testing to evaluate possible concomitant myasthenia gravis or other myositis-specific antibodies 2

Treatment Algorithm Based on Disease Severity

Mild Disease (Grade 1)

• If CK and/or aldolase are elevated and patient has muscle weakness, initiate oral prednisone at 0.5 mg/kg/day 2
• Offer analgesia with acetaminophen or NSAIDs for myalgia if no contraindications 2
• Consider holding statins if patient is taking them 2

Moderate Disease (Grade 2)

• Initiate prednisone 0.5-1 mg/kg/day 2
• If CK is elevated (3× ULN or more), use higher end of dosing range 2
• Refer to rheumatologist or neurologist 2
• Consider holding immune checkpoint inhibitors if that is the cause 2

Severe Disease (Grade 3-4)

• Initiate prednisone 1 mg/kg/day or equivalent 2
• For patients with severe compromise, start 1-2 mg/kg of methylprednisolone IV or higher dose bolus 2
• Consider hospitalization for patients with severe weakness limiting mobility, respiratory involvement, dysphagia, or rhabdomyolysis 2
• Urgent referral to rheumatologist and/or neurologist 2

Steroid-Sparing Agents

• Begin a steroid-sparing agent concurrently with corticosteroids to improve outcomes and reduce steroid-related side effects 1
• Options include:
  • Methotrexate 1, 3
  • Azathioprine 1, 4
  • Mycophenolate mofetil 1, 4

Corticosteroid Tapering Schedule

• Begin tapering corticosteroids after 2-4 weeks depending on patient response 1
• Taper by 10 mg every 2 weeks until reaching 30 mg/day, then by 5 mg every 2 weeks until reaching 20 mg/day, and finally by 2.5 mg every 2 weeks 1

Additional Therapies for Refractory Cases

• For patients who fail to respond to initial therapy, consider:
  • Intravenous immunoglobulin (IVIG) 3, 4
  • Rituximab (particularly effective in patients with certain myositis-specific autoantibodies) 5
  • Plasmapheresis in patients with acute or severe disease 2
  • Other immunosuppressants such as cyclophosphamide or cyclosporine for severe disease 1

Exercise Therapy

• Combining pharmacological treatment with individualized and supervised exercise is recommended based on evidence 5
• Exercise helps improve muscle performance and reduce disease activity 5

Monitoring and Follow-up

• Regular monitoring of muscle enzyme levels (CK) and inflammatory markers (ESR, CRP) 6
• MRI with T1-weighted, T2-weighted, and fat suppression techniques can help monitor treatment response 6

Common Pitfalls to Avoid

• 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
• Using TNF-α antagonists, which may exacerbate interstitial lung disease and myositis 3
• Failure to recognize cardiac involvement, which may require more aggressive therapy 2

Special Considerations

• For immune checkpoint inhibitor-related myositis, hold the immune checkpoint inhibitor therapy and follow grading system for management 2
• Permanently discontinue immune checkpoint inhibitors if there is evidence of myocardial involvement 2