Polymyositis / Dermatomyositis

Snapshot

• A 53-year-old woman with a past medical history of thyroid disease presents to her physician’s office for weakness. She reports that she has been feeling weak, has difficulty climbing the stairs, and combing her hair every morning. Today, she also has difficulty arising out of her chair. Physical exam reveals decreased strength, especially in the shoulders. She also has an impressive lilac periorbital rash and a sunburn on her cheeks. She is sent for further laboratory workup and counseled on the likely initiation of high-dose steroids.

Introduction

• Clinical definition
  • dermatomyositis is an autoimmune myopathy characterized by
    • symmetric proximal muscle weakness and rash
      • the clinical variants include amyopathic dermatomyositis (dermatomyositis without myositis)
  • polymyositis an autoimmune myopathy characterized by
    • symmetric proximal muscle weakness and no rash
• Epidemiology
  • incidence
    • rare
  • demographics
    • female > male
    • typically in adults 30-50 years of age
    • if in children, considered juvenile dermatomyositis
  • risk factors
    • drugs
    • physical exertion
• Pathogenesis
  • dermatomyositis
    • an antibody-driven autoimmune disease characterized by perimysial inflammation and atrophy, resulting in muscle tissue damage
      • perimysium is closer to the skin and therefore has cutaneous manifestations – “dermato”
    • associated with CD4 and complement activation
  • polymyositis
    • T-cell driven autoimmune disease characterized by endomysial inflammation
      • endomysium is farther from the skin and therefore has no cutaneous manifestations
    • associated with CD8
• Associated conditions
  • interstitial lung disease
  • malignancy which includes
    • breast or ovarian cancer
    • prostate cancer
    • lung cancer
  • other connective tissue diseases
• Prognosis
  • dermatomyositis
• ↑ risk of malignancy (typically develop within 5 years of diagnosis)

Presentation

• Symptoms
  • progressive weakness in hips and shoulders
  • dysphagia
  • dysphonia
    • laryngeal muscle weakness
• Physical exam
  • dermatomyositis
    • characteristic cutaneous findings
      • a photosensitive pink rash of the neck and trunk (shawl or V-sign, as it often appears as sunburn with V-neck t-shirt)
      • purple/lilac or red rash around eyes and on eyelids (heliotrope rash, can resemble malar rash) 
      • raised violaceous, slightly scaly plaques, on bony prominences of the hands and elbows (Gottron papules)   
      • Mechanic hands: thickening of the skin on the palms and radial aspects of the digits
  • polymyositis and dermatomyositis
    • proximal muscle weakness in the shoulders and hips
      • difficulty combing hair
      • difficulty raising arms
• difficulty rising from a chair

Studies

• Labs
  • ↑ creatinine phosphokinase (CPK or CK)
  • ↑ creatine kinase-MB (CK-MB)
  • ↑ aldolase
  • ↑ lactate dehydrogenase (LDH)
  • autoantibodies
    • + antinuclear antibody (ANA)
    • + anti-histidyl tRNA synthetase antibodies (anti-Jo-1) (~20% of patients)  
    • + anti-signal recognition particle (SRP) (~5% of patients)
      • usually associated with polymyositis
    • + anti-Mi-2 (<10% of adults)
      • usually associated with dermatomyositis
• Muscle biopsy 
  • indication
    • diagnostic gold standard to differentiate between inflammatory and non-inflammatory myopathies
  • findings
    • degenerating muscle fibers and inflammatory infiltrates
    • dermatomyositis 
      • perimysial inflammation
    • polymyositis
      • endomysial inflammation 
• Making the diagnosis
• based on clinical presentation and laboratory studies

Differential

• Systemic lupus erythematosus 
• Localized scleroderma 
• Infectious myopathy
• Myasthenia gravis 

Treatment

• Management approach
  • both diseases are often treated initially with a course of steroids followed by long-term immunosuppression
• Conservative
  • sun protection
    • indication
      • for all patients with dermatomyositis
• Medical
  • systemic steroids (high-dose)
    • indications
      • for all patients with myositis as first-line therapy
      • 2-4 weeks with subsequent taper
  • antimalarial
    • indications
      • for patients with primarily skin manifestations of dermatomyositis
      • drugs
        • hydroxychloroquine
  • non-steroidal immunosuppression
    • indications
      • for refractory disease
      • for prevention of recurrence after steroid taper
      • drugs
        • methotrexate
• azathioprine

Complications

• Cardiomyopathy
• Macrophage activation syndrome