A rare, acute hypersensitivity reaction most commonly triggered by herpes simplex virus (HSV) infections.

Etiology:- Infections (most common): herpes simplex virus (HSV), Mycoplasma pneumoniae, and fungal infections - Drugs: e.g., barbiturates, phenytoin, NSAIDs, penicillins, and sulfonamides- Immunizations (rare): e.g., after diphtheria, tetanus, influenza, hepatitis B vaccination

Clinical features:- Acute onset, with progression from erythematous macules to papules to target lesions (“bull’s-eye lesions”)- Symmetrical distribution- Affects backs of hands and feet first → spreads proximally and can affect the entire body, including palms and soles- EM minor: no/minimal involvement of mucus membranes- EM major: painful ulcers of the oral (most common), ocular, genital mucosa It is a distinct entity from SJS, and there is no risk of progression to TEN.- Further symptoms: fever, myalgia, and arthralgia in cases of EM major

Diagnosis: Clinical- Should be suspected (especially) if there is a history of recurrent labial herpes, recent drug intake, or immunizations.- Serology (PCR testing): in patients with suspected HSV/M. pneumoniae infections - Skin biopsy: indicated only in doubtful cases (e.g., no target lesions, recurrent EM)- As opposed to SJS or TEN, in EM the Nikolsky sign is negative.

Treatment: - Symptomatic; systemic corticosteroids are of no benefit.- Severe cases (EM major): hospitalize and treat as thermal burns- Recurrent EM: oral acyclovir for 4 months