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) concurrent with a steroid-sparing agent such as methotrexate, azathioprine, or mycophenolate mofetil. 1

Diagnostic Workup

• Complete rheumatologic and neurologic history and examination, including muscle strength assessment and skin examination for findings suggestive of dermatomyositis 2
• Blood tests to evaluate muscle inflammation: CK, aldolase, transaminases (AST, ALT), and LDH 2
• Troponin to evaluate myocardial involvement 2
• Inflammatory markers (ESR and CRP) 2
• Consider EMG, MRI, and/or muscle biopsy when diagnosis is uncertain 2
• Autoantibody testing to evaluate possible concomitant myasthenia gravis and other myositis-specific antibodies 2

Treatment Algorithm Based on Severity

Grade 1 (Mild weakness with or without pain)

• Continue immunotherapy if applicable 2
• If CK and/or aldolase are elevated and patient has muscle weakness, offer oral corticosteroids starting at 0.5 mg/kg/day 2
• Provide analgesia with acetaminophen or NSAIDs for myalgia if no contraindications exist 2
• Consider holding statins if patient is taking them 2

Grade 2 (Moderate weakness limiting instrumental ADLs)

• Hold immunotherapy temporarily if applicable 2
• Initiate prednisone 0.5-1 mg/kg/day if CK is elevated (≥3× ULN) 2
• Provide NSAIDs as needed for pain 2
• Refer to rheumatologist or neurologist 2
• Consider early initiation of steroid-sparing agents 1, 3

Grade 3-4 (Severe weakness limiting self-care ADLs)

• Hold immunotherapy and consider permanent discontinuation if myocardial involvement 2
• Consider hospitalization for patients with severe weakness 2
• Urgent referral to rheumatologist and/or neurologist 2
• Initiate prednisone 1 mg/kg/day or equivalent 2
• For severe cases, consider IV methylprednisolone 1-2 mg/kg or higher-dose bolus (250-1000 mg) for 1-5 consecutive days 2, 1
• Consider plasmapheresis in patients with acute or severe disease 2
• Consider IVIG therapy, particularly for refractory dermatomyositis 2, 4
• Consider other immunosuppressant therapy if symptoms worsen or don't improve after 2 weeks 2

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

Steroid-Sparing Agents

• Initiate steroid-sparing agents early in treatment to reduce corticosteroid-related side effects 1, 3
• Options include:
  • Methotrexate 2, 1, 3
  • Azathioprine 2, 1, 3
  • Mycophenolate mofetil 2, 1, 3
  • For refractory cases: rituximab, especially in patients with certain myositis-specific autoantibodies 5, 3

Monitoring and Follow-up

• Monitor muscle enzyme levels (CK, aldolase) and inflammatory markers (ESR, CRP) 2, 1
• Use MRI with T1-weighted, T2-weighted, and fat suppression techniques to monitor treatment response in selected cases 1
• Regular assessment of muscle strength and function 2

Common Pitfalls and Considerations

• Failure to screen for malignancy in adult patients, especially with dermatomyositis 1
• Inadequate initial dosing of corticosteroids 1, 6
• Delaying initiation of steroid-sparing agents 1, 3
• TNF-α antagonists should be avoided as they may exacerbate interstitial lung disease and myositis 6
• Caution with rechallenging immunotherapy in immune checkpoint inhibitor-induced myositis 2
• Exercise should be combined with pharmacological treatment based on evidence 5

Special Considerations

• For immune checkpoint inhibitor-induced myositis, high-dose systemic glucocorticoids are first-line treatment 1
• Management of immune-mediated necrotizing myopathy is similar to dermatomyositis/polymyositis but may require more aggressive therapy 1
• For juvenile dermatomyositis, begin corticosteroids at 2 mg/kg up to 60 mg/day with concurrent methotrexate 1