Epidemiology
Etiology
Erythema multiforme is a type IV hypersensitivity reaction which can be triggered by the following.
- Infections (most common): herpes simplex virus (HSV) (50% of cases), Mycoplasma pneumoniae, and fungal infections
- Drugs: e.g., barbiturates, phenytoin, NSAIDs, beta-lactam antibiotics (e.g., penicillins), and sulfonamides
Pathophysiology
Clinical features
- Rash
- Acute onset, with progression from erythematous macules to papules and vesicles to target lesions
- Target lesions
- Characteristic of EM, appear a few days after the onset of rash, may be absent in some patients
- Target lesions have 3 zones: an inner dark red/brown zone, surrounded by a pale zone, and an outer erythematous ring
- Epithelial necrosis is present in the inner zone
Diagnostics
Treatment
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