What is the recommended workup and treatment for myositis?

Myositis Workup and Treatment

The recommended workup for myositis includes comprehensive rheumatologic and neurologic evaluation, muscle enzyme testing, inflammatory markers, and appropriate imaging, followed by first-line treatment with corticosteroids (prednisone 0.5-1 mg/kg/day) with early addition of steroid-sparing agents. 1

Diagnostic Workup

Laboratory Testing

• Muscle enzymes:
  • Creatine kinase (CK) - primary marker
  • Aldolase
  • Lactate dehydrogenase (LDH)
  • Aspartate aminotransferase (AST)
  • Alanine aminotransferase (ALT)
• Inflammatory markers:
  • Erythrocyte sedimentation rate (ESR)
  • C-reactive protein (CRP)
• Myositis-specific autoantibodies
• Complete blood count
• Comprehensive metabolic panel

Imaging

• MRI of affected muscles - most sensitive imaging modality
• Electromyography (EMG) to assess muscle electrical activity

Tissue Diagnosis

• Muscle biopsy - gold standard for definitive diagnosis
• Skin biopsy (for dermatomyositis)

Treatment Algorithm

Initial Treatment

1. Corticosteroids - First-line therapy 1

   • Prednisone 0.5-1 mg/kg/day orally
   • For severe disease: Consider IV methylprednisolone pulse therapy (may lead to quicker recovery and reduced long-term steroid exposure) 2
   • Continue initial dose until CK normalizes 3

2. Early addition of steroid-sparing agents 1, 4

   • First-line steroid-sparing options:
     • Methotrexate
     • Azathioprine

Corticosteroid Management

• Maintain initial dose until CK normalizes 3
• Slow taper only after clinical improvement and normalization of CK 3
• Monitor CK levels closely during taper - rising CK, even within normal range, may signal impending relapse 3

Treatment for Refractory Disease

For patients with inadequate response to initial therapy:

1. Intravenous immunoglobulin (IVIg) 4, 5

   • Recent evidence suggests early add-on IVIg may lead to faster improvement and better outcomes 5

2. Additional options (in order of preference) 4, 6:

   • Rituximab
   • Mycophenolate mofetil
   • Tacrolimus

Special Considerations

Subtype-Specific Approaches

• Dermatomyositis/Polymyositis: Most patients require combination of prednisone with azathioprine or methotrexate 4
• Inclusion Body Myositis: Trial of oral prednisone with methotrexate may be considered 4
• Immune-mediated Necrotizing Myopathy: Often requires aggressive immunosuppression 6

Monitoring and Follow-up

• Regular assessment of muscle strength
• Serial CK measurements
• Achieving CK in low-normal range predicts prolonged remission 3
• Monitor for steroid-related complications, particularly myopathy and osteoporosis 2

Treatment Pitfalls to Avoid

• Tapering corticosteroids too quickly
• Reducing corticosteroid dose while CK remains elevated 3
• Failing to monitor for steroid-related complications
• Delaying initiation of steroid-sparing agents
• Not recognizing rising CK within normal range as a potential sign of relapse 3