Dermatomyositis

1. See Also
   1. Polymyositis
2. Epidemiology
   1. Twice as common in women
   2. Mean age at diagnosis
      1. Adults: 40 years
      2. Children: 5 to 14 years
3. Pathophysiology
   1. Group 2 of Polymyositis disorders (accounts for 25%)
   2. Classification
      1. Without Muscle Weakness (amyopathic Dermatomyositis)
      2. With Muscle Weakness
         1. Pediatric Dermatomyositis
         2. Adult Dermatomyositis (with or without cancer)
4. Signs: Pathognomonic for Dermatomyositis
   1. Gottron's Papules (33% to 70% of patients)
      1. Violaceous flat topped Papules
      2. Distribution
         1. Dorsal interphalangeal joints of hand
         2. Dorsal metacarpophalangeal joints
         3. Knees
         4. Elbows
         5. Medial malleoli
   2. Gottron's Sign
      1. Symmetric erythematous or violaceous Plaques
         1. Smooth and usually non-Scaling
         2. Edema is variably present
      2. Distribution
         1. Same as Gottron's Papules
         2. Extends over extensor tendons on hands and Forearms
         3. Spares interphalangeal spaces (unlike SLE)
5. Signs: Characteristic Findings
   1. Facial photosensitivity and dusky erythema on face
      1. Classic lilac-colored (heliotrope) rash
      2. Occurs in 30 to 60% of patients early in disease
      3. Distribution
         1. Eyelids and periorbital area
         2. Bridge of nose
         3. Malar area
   2. Erythematous, poikilodermatous Macules
      1. V-area of neck (V-sign)
      2. Shoulders and upper back (Shawl sign)
   3. Periungual telangiectases
   4. Mechanic's hand
      1. Fissured, scaly, hyperkeratotic, hyperpigmented hands
6. Signs: Other Findings
   1. Poikiloderma atrophicans vasculare
      1. Circumscribed violaceous erythema
      2. Occurs late in Dermatomyositis
      3. Associated findings
         1. Central atrophy
         2. Telangiectasia
         3. Hypopigmentation
      4. Distribution
         1. Posterior Shoulders, back and buttocks
         2. V-shaped area of anterior neck and chest
   2. Calcinosis cutis
      1. Calcium deposits
      2. Occurs in 30-70% of children and 10% of adults
      3. Distribution
         1. Buttocks
         2. Elbows
         3. Knees
         4. Areas of local trauma
7. Associated Systemic Signs and Conditions
   1. See Polymyositis
   2. Common Systemic Associations
      1. Proximal Muscle Weakness
      2. Dysphonia
      3. Dysphagia
   3. Less common systemic associations
      1. Respiratory Muscle Weakness
      2. Visual changes
      3. Abdominal Pain
   4. Malignancy (only seen in adult Dermatomyositis)
      1. Highest risk over age 45 years
      2. Most commonly associated cancers
         1. Ovarian Cancer
         2. Gastric Cancer
         3. Lymphoma
      3. Less commonly associated cancers
         1. Lung Cancer
         2. Cancer of male genitalia
         3. Skin cancer (Melanoma and non-Melanoma)
         4. Kaposi's Sarcoma
         5. Mycosis Fungoides
8. Subtypes
   1. Juvenile Dermatomyositis findings
      1. Low-grade fever
      2. Gastrointestinal symptoms
      3. Symmetric arthritis of large and small joints
      4. Cardiac conduction delay
      5. Truncal Muscle Weakness (may use Gower's Sign)
      6. No malignancy association
   2. Overlap Syndrome (comorbid connective tissue disease)
      1. Rheumatoid Arthritis
      2. Scleroderma
      3. Systemic Lupus Erythematosus
      4. Sjogren's Syndrome
      5. Polyarteritis Nodosa
      6. Mixed connective tissue disease
   3. Amyopathic Dermatomyositis (2-11%)
      1. Pathognomonic skin changes without Myositis
      2. Presenting symptoms
         1. Lethargy or Fatigue
         2. Pruritus
         3. Photosensitivity
         4. Arthralgias
9. Differential Diagnosis
   1. See Dermatomyositis Differential Diagnosis
10. Radiology
    1. Chest XRay
11. Labs: Initial Evaluation
    1. Myositis Labs
       1. Alanine Aminotransferase (ALT)
       2. Aspartate Aminotransferase (AST)
       3. Lactate Dehydrogenase (LDH)
       4. Creatine Phosphokinase (CPK)
    2. Urinalysis for creatinuria or Myoglobinuria
    3. Sedimentation rate (ESR) elevated
    4. Complete Blood Count (CBC) identifies Anemia
    5. Antinuclear Antibody (ANA)
    6. Serum chemistry panel
    7. Stool Guaiac
12. Labs: Secondary Evaluation
    1. See Dermatomyositis Evaluation
    2. Electromyogram (EMG) shows myopathic pattern
    3. Consider biopsy
       1. Muscle biopsy
       2. Skin biopsy (to rule-out other causes)
13. Management
    1. See Dermatomyositis Management
14. References
    1. Callen (2000) Lancet 355(9197):53-7
    2. Caro (2001) Semin Cutan Med Surg 20(1):38-45
    3. Koler (2001) Am Fam Physician 64(9):1565-72
    4. Kovacs (1998) J Am Acad Dermatol 39(6):899-920
    5. Pachman (1995) Pediatr Clin North Am 42:1071-98