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Case 1: Vacuolar degeneration of basal keratinocytes and necrotic keratinocytes are key features of EM.

A closer look reveals scattered necrotic keratinoctyes and perivacular lymphoctyes. Exocytosis of lymphocytes is also common.


It is a common condition, mostly affecting children and young adults. Clinically, "multiforme" (many forms) lesions are seen which include papules, plaques, blisters and target lesions. They most often affect the palms and trunk. If one finds the classic "target lesions", it is most likely due to a herpes simplex infection (Rapini).

Histologically, there is a lichenoid infiltrate with basal layer liquefaction. Small subepidermal blisters may be present. Necrotic keratinocytes are scattered throughout the epidermis.

Stevens-Johnson syndrome involves the mucous membranes with epidermal necrosis and toxic epidermal necrolysis, the most severe form on the erythema multiforme spectrum, is usually due to drugs (e.g. sulfonamides, phenytoin). In TEN, there is sloughing of skin, extensive skin necrosis and can lead to death (Rapini, Sternberg).


Many cases are a reaction to HSV infection. Eruptions typically arise in crops that persist for about 1-4 weeks. Outbreaks may occur only once, but may also be recurrent. They may be accompanied by low-grade fever and myalgia.


Usually resolves on its own. Patients with severe outbreaks may use acyclovir at first sign of an episode.


→Erythema multiforme is commonly associated with HSV infection.

→Histologic features include basal layer liquefaction, necrotic keratinocytes, spongiosis and exocytosis of lymphocytes. There may be subepidermal blistering as well.

→More severe forms (Stevens-Johnson syndrome) and toxic epidermal necrolysis (TEN) may be life threatening. TEN is associated with use of drugs (e.g. sulfonamides, phenytoin).


Rapini RP. Practical Dermatopathology. Philadelphia, PA: Elsevier; 2005: 62-3.

Mills SE, ed. Sternberg's Diagnostic Surgical Pathology.4th Ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2004: 15.

Last updated: 2012-02-10
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