What is the initial treatment for myositis?

Initial Treatment for Myositis

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

Diagnosis and Assessment

Before initiating treatment, a thorough evaluation should include:

• Complete rheumatologic and neurologic examination with focus on muscle strength and skin examination for findings suggestive of dermatomyositis 2
• Blood testing to evaluate muscle inflammation:
  • Creatine kinase (CK) and aldolase 2
  • Transaminases (AST and ALT) and LDH which can also be elevated 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 or other myositis-specific antibodies 2

Treatment Algorithm Based on Severity

Mild Disease (Grade 1)

• Mild weakness with or without pain
• Treatment:
  • If CK and/or aldolase are elevated and muscle weakness is present, initiate oral prednisone at 0.5 mg/kg/day 2, 1
  • 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)

• Moderate weakness with or without pain limiting age-appropriate instrumental ADL
• Treatment:
  • Initiate prednisone 0.5-1 mg/kg/day 2, 1
  • Concurrently start a steroid-sparing agent (methotrexate, azathioprine, or mycophenolate mofetil) 1, 3
  • Refer to rheumatology or neurology 2
  • If CK is significantly elevated (≥3x ULN), use higher dose of prednisone (closer to 1 mg/kg/day) 2

Severe Disease (Grade 3-4)

• Severe weakness limiting self-care ADL
• Treatment:
  • Consider hospitalization for patients with severe weakness, respiratory involvement, dysphagia, or rhabdomyolysis 2
  • Initiate prednisone 1 mg/kg/day or equivalent 2
  • For severe cases, consider IV methylprednisolone 1-2 mg/kg or higher dose bolus 2, 1
  • Urgent referral to rheumatology and/or neurology 2
  • Consider additional therapies for refractory cases:
    • IVIG (particularly effective in dermatomyositis) 2, 3, 4
    • Rituximab (especially in patients with certain myositis-specific antibodies) 5
    • Consider plasmapheresis in acute or severe disease as guided by specialists 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 1
• Then taper by 5 mg every 2 weeks until reaching 20 mg/day 1
• Finally, taper by 2.5 mg every 2 weeks 1

Monitoring Response

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

Important Considerations and Pitfalls

• Early recognition and treatment is critical to prevent irreversible muscle damage 2
• Corticosteroids alone are often insufficient; early introduction of steroid-sparing agents is recommended to reduce steroid-related side effects 1, 6
• TNF-α antagonists should generally be avoided in myositis patients as they may exacerbate interstitial lung disease and increase infection risk 3
• Failure to screen for underlying malignancy, particularly in dermatomyositis patients, is a common pitfall 1
• Exercise therapy should be combined with pharmacological treatment for optimal outcomes 5
• If there is no response to initial therapy, consider re-evaluation of the diagnosis with possible repeat muscle biopsy 3

By following this treatment algorithm with early aggressive immunosuppression and appropriate monitoring, most patients with inflammatory myositis can achieve improvement in muscle strength and function, reducing long-term morbidity and mortality.