At age 3 weeks, this 5-month-old boy developed a raised erythematous rash on his scalp and upper trunk that was unresponsive to hydrocortisone cream. The rash spread to his lower trunk and diaper area, and he become febrile (up to 40°C) daily. Episodic diarrhea occurred up to 10 times daily, with vomiting. Langerhans' cell histiocytosis was diagnosed on skin biopsy. Blood was noted in his stools at age 4½ months, as was failure to gain weight. Fever and hematochezia persisted until hospital admission at age 5 months.
His height was at the 50th percentile for age, and his weight at the 25th percentile. A scaly, erythematous rash covered his face, scalp, trunk, and perineum. The liver edge was palpable 5 cm below the costal margin, but there was no splenomegaly or lymph node enlargement. Laboratory values were as follows: hemoglobin, 96 g/L; hematocrit, 0.29; white blood cell count,