Erythema Multiforme

Question 1

Definition

Answer 1

• Acute, self-limiting but often relapsing, mucocutaneous inflammatory condition. It is a hypersensitivity reaction characterised by target lesions.

Question 2

Aetiology

Answer 2

• Infection (most common cause)
  
  • HSV
  • Mycoplasma
  • Hepatitis B
  • EBV
  • CMV
• Vaccination
  
  • Smallpox
• Medicine
  
  • Antibiotics (i.e. aminopenicillins, quinolones)
  • Anticonvulsants (i.e. carbamazepine, phenytoin)
  • Oral contraceptives

Question 3

Signs and symptoms

Answer 3

• Signs/symptoms include target lesions (at least 3 zones), recurrent disease and mucosal erosions.
• Risk factors include prior occurrence, HSV and mycoplasma pneumoniae.

Question 4

Pathophysiology

Answer 4

• Monocytic inflammatory cell infiltrate can be found suggesting a type IV cytotoxic hypersensitivity response caused by T lymphocytes reacting to specific antigens, producing cytotoxic immune complexes.
• These complexes cause keratinocyte oedema, necrosis and blistering – there is no epidermal necrosis and the inflammatory infiltrate is within the dermis.

Question 5

Investigation

Answer 5

• FBC
  
  • Abnormal WBC
• U&Es
  
  • Volume depletion
• HSV serology
  
  • Positive
• Rapid PCR
  
  • Positive for varicella DNA
• Cold-haemagglutination serology
  
  • Positive for M pneumoniae infection
• M pneumoniae titres
  
  • Positive

Question 6

Treatment

Answer 6

• Treat underlying cause
• Topical emollient
• Topical or oral corticosteroids (i.e. triamcinolone acetonide)
• Sterile dressings
• Oral analgesia
• Oral antiviral therapy (for HSV)
• Macrolide of doxycycline (for M pneumoniae)

Question 7

Complications

Answer 7

• Bacterial infections

Question 8

Prevention and prognosis

Answer 8

• Secondary prevention
  
  • Avoid radiation and UV light where possible
• Prognosis
  
  • Self-limiting in 2-3 weeks with no scarring