A 12-Month-Old Healthy Girl with a New Oral Ulcer and Chronic Diaper Rash.

A 12-month-old healthy girl presented with a chronic diaper rash. Physical examination demonstrated crusting of the scalp, erythematous papules with surrounding petechiae on the lower abdomen, and an intraoral palatal ulcer. Further imaging demonstrated bone involvement. Histopathologic examination of involved skin and the intraoral ulcer demonstrated epithelioid histiocytes with "coffee bean-shaped" nuclei, staining positive for CD1a and langerin by immunohistochemistry, consistent with Langerhans cell histiocytosis (LCH). LCH is a disease entity of unknown etiology characterized by histiocytic proliferation that most commonly presents in young children. The cutaneous findings of LCH include a seborrheic dermatitis-like and/or red-brown papular eruption. Intraoral examination is crucial as oral mucosal and maxillofacial skeletal disease can also be seen in LCH. When a child presents with a recalcitrant seborrheic dermatitis-like eruption or chronic diaper rash, the clinician should be alerted to the possibility of LCH. Timely recognition and diagnosis of LCH is important for oncologic referral, evaluation, and treatment.