What is the initial treatment for myositis?

Initial Treatment for Myositis

The initial treatment for myositis should begin with high-dose corticosteroids (prednisone 0.5-1 mg/kg/day, typically 60-80 mg daily) concurrently with a steroid-sparing immunosuppressive agent such as methotrexate, azathioprine, or mycophenolate mofetil. 1, 2

First-Line Treatment Algorithm

• Begin prednisone at 0.5-1 mg/kg per day (typically 60-80 mg daily as a single dose) for all patients with inflammatory myositis 1, 2
• Concurrently initiate a steroid-sparing immunosuppressive agent to improve outcomes and reduce steroid-related side effects 1, 2
• Options for steroid-sparing agents include:
  • Methotrexate (preferred first choice by many experts) 1, 2
  • Azathioprine (alternative option) 1, 2
  • Mycophenolate mofetil (suitable alternative) 1, 2

Corticosteroid Tapering Schedule

• Begin tapering corticosteroids after 2-4 weeks depending on patient response 2
• Follow a structured tapering schedule:
  • Taper by 10 mg every 2 weeks until reaching 30 mg/day 2
  • Then taper by 5 mg every 2 weeks until reaching 20 mg/day 2
  • Finally taper by 2.5 mg every 2 weeks 2
• Do not taper corticosteroids until serum creatine kinase (CK) has normalized, as tapering while CK remains elevated often results in disease flare 3

Treatment for Severe Disease

• For patients with severe myositis or extensive extramuscular involvement:
  • Consider high-dose methylprednisolone pulse therapy (10-20 mg/kg or 250-1000 mg given on 1-5 consecutive days) 2
  • Consider additional therapies such as cyclophosphamide, cyclosporine, or intravenous immunoglobulin (IVIG) 1, 2
• IVIG therapy is indicated for patients with Grade 3-4 myositis who have inadequate response to corticosteroids 4
• Standard IVIG dosing is 1-2 g/kg of ideal body weight, usually given over 2 consecutive days once monthly for 1-6 months 4

Monitoring and Follow-up

• Regularly monitor muscle enzyme levels (CK, transaminases, LDH, aldolase) and inflammatory markers (ESR, CRP) 1, 2
• Use MRI with T1-weighted, T2-weighted, and fat suppression techniques to monitor treatment response 1, 2
• Aim to achieve CK within the low normal range, as this predicts prolonged biochemical remission 3
• A rise in CK, even within the normal range, may signal an impending clinical relapse 3

Special Considerations

• For juvenile dermatomyositis, begin corticosteroids at 2 mg/kg up to a maximum of 60 mg/day and add subcutaneous methotrexate at treatment onset at 15 mg/m² once weekly 2
• For immune checkpoint inhibitor-related myositis:
  • Hold immune checkpoint inhibitor therapy 1
  • Resume upon symptom control for grade 2 toxicity 1
  • For grade 3-4 toxicity, hold and potentially resume in consultation with rheumatology 1
  • Approximately 10% of patients may require intravenous methylprednisolone pulses 1, 2

Common Pitfalls to Avoid

• Failure to screen for malignancy in adult patients, especially with dermatomyositis 1, 2
• Inadequate initial dosing of corticosteroids (underdosing) 1, 2
• Delaying initiation of steroid-sparing agents 1, 2
• Tapering corticosteroids too quickly or before CK has normalized 3
• Failure to check IgA levels before administering IVIG (can lead to severe anaphylactic reactions in IgA-deficient patients) 4

Evidence for Early Combination Therapy

• Early immunosuppression or immunomodulation by intensive treatment may induce faster reduction of disease activity and prevent chronic disability 5
• Adding immunosuppressive agents early rather than later in the disease course is associated with better outcomes 6
• Prolonged administration of high doses of corticosteroids alone should be avoided 6
• Recent evidence suggests that early add-on IVIG may lead to greater clinical response after 12 weeks compared to prednisone monotherapy 5