Primary cutaneous Langerhans cell histiocytosis in an adult.

An unusual adult case of Langerhans cell histiocytosis is presented. The case initially mimicked granuloma annulare, both clinically and histologically. The patient subsequently had development of extensive cutaneous involvement that pathologically revealed a diffuse infiltrate of CD1-positive histiocytic cells containing Langerhans granules. Extensive investigations failed to detect systemic involvement. The patient's cutaneous eruption did not respond to various therapeutic interventions, including phototherapy with oral psoralen with long-wave UV radiation in the A range (PUVA) and systemic vinblastine sulfate. Marked but temporary clinical and histologic improvement was achieved with total body electron beam radiotherapy. The nosology of this case is discussed in the context of the various histiocytic proliferative disorders.