Understanding the pathogenesis of HSV-associated erythema multiforme.

Erythema multiforme (EM) is a polymorphic, often recurring eruption caused by exposure to medication or various infections, notably herpes simplex virus (HSV). Understanding the pathogenesis of HSV-associated EM (HAEM) is essential for patient management. We suggest that HAEM results from the combination of viropathic effects mediated by HSV proteins, notably DNA polymerase (Pol), and an immunological reaction to viral antigens. Presumably, viral DNA and proteins ingested by macrophages at HSV lesion sites undergo fragmentation and processing for presentation to T cells with HSV memory. HSV DNA is deposited on the skin, where it is expressed. Activated T cells are recruited to the skin site of Pol expression, directly or indirectly resulting in the generation of an inflammatory cascade. Factors potentially involved in the incidence of recurrences, lesion severity and anatomical localization include the identity of the deposited HSV genes, cutaneous capillary size, degree of vasoconstriction and ambient temperature. Evidence in support of this interpretation is reviewed.