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.

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Reticular erythematous mucinosis is an uncommon type of cutaneous mucinosis. Typically, reticular erythematous mucinosis affects middle-aged women and usually appears as papules and plaques on the mid-upper trunk. Histologically, biopsies of reticular erythematous mucinosis reveal increased deposition of dermal mucin and perivascular lymphocytic inflammation. Infrequently, reticular erythematous mucinosis has been reported in males and in atypical locations other than the trunk. In these instances, reticular erythematous mucinosis can present a diagnostic challenge clinically and histologically. This case describes the clinical and histologic findings of a localized variant of reticular erythematous mucinosis in a 65-year-old male patient.