Erythema Multiforme (EM)

Erythema multiforme is an acute, immune-mediated condition characterized by distinctive target-like lesions on the skin and sometimes mucous membranes.

Key Points

• Typically self-limiting condition lasting 2-4 weeks
• Most common in children and young adults
• Can be recurrent in some cases
• Two main forms: EM minor and EM major
• Not the same as Stevens-Johnson Syndrome (SJS)

Epidemiology

• Peak incidence: 20-40 years
• Male:Female ratio = 3:2
• Can occur at any age
• Higher incidence in pediatric population
• Recurrence rate: 20-25%

Pathophysiology

Triggers

• Infectious Causes (70%):
  • Herpes Simplex Virus (HSV) - most common
  • Mycoplasma pneumoniae
  • Epstein-Barr virus
  • Streptococcal infections
  • Adenovirus
• Medication-Related (10%):
  • Sulfonamides
  • NSAIDs
  • Anticonvulsants
  • Antibiotics
• Idiopathic (20%)

Immunologic Mechanism

• Type IV hypersensitivity reaction
• Cell-mediated immune response
• Cytotoxic T-cell attack on keratinocytes
• Release of inflammatory mediators
• Immune complex deposition

Molecular Basis

• Cytokine cascade activation
• TNF-α and IFN-γ production
• Fas-FasL interaction
• Keratinocyte apoptosis

Clinical Features

Classic Target Lesions

• Morphology:
  • Three distinct zones
  • Central dusky or dark area
  • Pale middle ring
  • Erythematous outer ring
  • Symmetric, round lesions
• Distribution:
  • Acral distribution (hands, feet)
  • Extensor surfaces
  • Symmetrical pattern
  • Palm and sole involvement common

Clinical Variants

• EM Minor:
  • Cutaneous lesions only
  • Less than 10% BSA involvement
  • No or minimal mucosal involvement
  • Better prognosis
• EM Major:
  • Extensive cutaneous involvement
  • Significant mucosal involvement
  • More severe systemic symptoms
  • Can affect multiple mucosal sites

Associated Symptoms

• Prodromal Symptoms:
  • Fever
  • Malaise
  • Arthralgia
  • Upper respiratory symptoms
• Mucosal Symptoms:
  • Pain
  • Burning sensation
  • Difficulty eating/drinking
  • Photophobia (if ocular involvement)

Diagnosis

Clinical Assessment

• Detailed History:
  • Recent infections
  • Medication changes
  • Previous episodes
  • Timeline of symptoms
  • Associated symptoms
• Physical Examination:
  • Characterization of lesions
  • Distribution pattern
  • Mucosal involvement
  • Systemic signs

Laboratory Studies

• Essential Tests:
  • HSV PCR/culture
  • Complete blood count
  • Basic metabolic panel
  • Liver function tests
• Additional Studies:
  • Mycoplasma testing
  • Skin biopsy (if diagnosis unclear)
  • Direct immunofluorescence
  • Viral studies

Differential Diagnosis

• Major Considerations:
  • Stevens-Johnson Syndrome
  • Toxic Epidermal Necrolysis
  • Fixed drug eruption
  • Urticaria
  • Bullous pemphigoid

Management

General Measures

• Supportive Care:
  • Discontinue triggering medications
  • Pain management
  • Wound care
  • Fluid/electrolyte balance
• Specific Interventions:
  • Antiviral therapy if HSV-related
  • Topical steroids
  • Oral antihistamines
  • Wound dressings

Pharmacologic Treatment

• First-Line:
  • Acyclovir (if HSV-associated)
  • Topical corticosteroids
  • Oral antihistamines
• Second-Line:
  • Systemic corticosteroids
  • Immunosuppressants
  • Immunomodulators

Preventive Measures

• Long-term Management:
  • Prophylactic antivirals
  • Trigger avoidance
  • Regular monitoring
  • Patient education

Complications

Potential Complications

• Mucosal Complications:
  • Scarring
  • Strictures
  • Synechiae
  • Vision problems
• Systemic Complications:
  • Dehydration
  • Secondary infection
  • Nutritional deficiencies
  • Psychological impact

Special Considerations

Pediatric Considerations

• Age-specific management
• Growth and development monitoring
• School/activity adjustments
• Family support and education

Monitoring and Follow-up

• Regular assessment of:
  • Disease progression
  • Treatment response
  • Complications
  • Recurrence prevention

Prognosis

• Generally good for EM minor
• Variable for EM major
• Risk factors for poor outcomes
• Long-term implications