Rheumatoid arthritis and erythema multiforme: a possible pathogenetic link for T-cell-mediated autoimmune and reactive skin diseases?

We present a case of a woman with a 14-year history of rheumatoid arthritis, who showed simultaneously and gradually appearing, annular, erythematous, itchy patches and exacerbation of the joint symptoms, of one month duration, after pregnancy. Clinical and histologic features led us to the diagnosis of erythema multiforme. While it is not possible to exclude that the co-occurrence of the two conditions is coincidental, our case suggests the possibility that erythema multiforme is a sign of an ample alteration of the immune system that may occur in patients with systemic immune diseases as a consequence of the action of various triggering factors, such as molecular mimicry between endogenous and exogenous antigens or pregnancy, which is notoriously a period of complex and still largely unexplored alterations in the immune system reactivity.