Dermatomyositis

Background

• Inflammatory myopathy
• Affects proximal muscles > distal
• Female:Male; 2:1
• Peak incidence 40-50s

Clinical Features

Heliotrope rash

Muscular

• Proximal greater than distal weakness
  • Deltoid and hip flexors
  • difficulty standing from a chair
• Onset over months
• Mild myalgias

Dermatologic

• Heliotrope rash on face scalp
• Gottron's papules (rash on MCP, PIP, and DIP joints)
• Shawl sign (rash above shoulders)

Other

• Cardiac (cardiomyopathy)
• High association with malignancy
• Interstial lung disease

Differential Diagnosis

• Drug Induced Myopathies (Statins)

Weakness

• Neuromuscular weakness
  • UMN:
    • CVA
    • Hemorrhagic stroke
    • Multiple sclerosis
    • Amyotrophic Lateral Sclerosis (ALS) (UMN & LMN)
  • Spinal cord disease:
    • Infection (Epidural abscess)
    • Infarction/ischemia
    • Trauma (Spinal Cord Syndromes)
    • Inflammation (Transverse Myelitis)
    • Degenerative (Spinal muscular atrophy)
    • Tumor
  • Peripheral nerve disease:
    • Guillain-Barre syndrome
    • Toxins (Ciguatera)
    • Tick paralysis
    • DM neuropathy (non-emergent)
  • NMJ disease:
    • Myasthenia gravis crisis
    • Botulism
    • Organophosphate toxicity
    • Lambert-Eaton myasthenic syndrome
  • Muscle disease:
    • Rhabdomyolysis
    • Dermatomyositis
    • Polymyositis
    • Alcoholic myopathy
• Non-neuromuscular weakness
  • Can't miss diagnoses:
    • ACS
    • Arrhythmia/Syncope
    • severe infection/Sepsis
    • Hypoglycemia
    • Periodic paralysis (electrolyte disturbance, K, Mg, Ca)
      • Hypokalemic periodic paralysis
      • Thyrotoxic periodic paralysis
    • Respiratory failure
  • Emergent Diagnoses:
    • Symptomatic Anemia
    • Severe dehydration
    • Hypothyroidism
    • Polypharmacy
    • Malignancy
  • Other causes of weakness and paralysis
    • Acute intermittent porphyria (ascending weakness)

Evaluation

• CK
• ANA
• Anti-Jo-1
• Chem for creatinine
• Troponin, can involve myocardium
• ECG
• Bedside PFTs (FEV1 and FVC)
• Urinalysis for myoglobin
• Consider malignancies
• Signs of systemic inflammation
  • Fever
  • ESR elevated in 50% of patients, does not correlate with disease activity
  • Elevated CRP

Management

Mild disease

• Prednisone 1mg/kg/day (up to 80mg/day)
  • Taper after 6-8 weeks

Severe disease

• Respiratory muscle symptoms of CHF
  • Methylprednisolone 1000mg/day x 3 days

Disposition

• Admit to monitored bed for CHF symptoms, respiratory muscle weakness
• Admit for dysphagia/aspiration risk
• Out patient follow up with muscle biopsy for others
• Very strongly associated with malignancy (~30%), especially:
  • Ovarian
  • Lung
  • Pancreatic
  • Stomach
  • Colorectal
  • Lymphoma
  • Bladder

See Also

• Weakness

References

Authors

Alex Linker, Kevin Lu, Ross Donaldson, Claire, Daniel Ostermayer, Neil Young