Acrosyringeal concentration of necrotic keratinocytes in erythema multiforme: a clue to drug etiology. Clinicopathologic review of 29 cases.

Erythema multiforme (EM) is caused by various insults, frequently an infectious agent or a drug. It is current practice that histologic identification of the precipitating factor is not possible. We have observed a pattern of acrosyringeal concentration of keratinocyte necrosis in certain cases of EM and retrospectively studied 29 consecutive cases of EM to establish clinicopathologic correlation for this finding. Acrosyringeal concentration was observed in 10 of 29 specimens, all 10 clinically drug related (Group 1). Nineteen specimens lacked this pattern (Group 2) of which 3 cases were clinically drug related (sensitivity = 0.8, specificity = 1.0). Eosinophils were present in the dermal infiltrate of 6 specimens from Group 1 and 2 specimens from Group 2 (p = 0.025). Acrosyringeal concentration of keratinocyte necrosis in EM occurs in drug-related cases and is more likely to be accompanied by a dermal inflammatory infiltrate containing eosinophils. Drug concentration in sweat may explain this pattern with subsequent toxic and immunologic mechanisms leading to the fully evolved lesion.