Solitary Langerhans cell histiocytoma: an unusual form of Hashimoto-Pritzker histiocytosis?

A 2-month-old girl acutely developed a brownish, firm nodule on the left thigh. The lesion was surgically removed when the patient was age 3 months, and histology showed a massive dermal infiltration by large histiocytic cells with abundant ground glass cytoplasm. Most cells were S100 protein positive. Electron microscopic examination revealed the presence of Birbeck granules in about 30% of the histiocytes, as well as laminated dense bodies and wormlike bodies. No recurrence was observed during follow-up for three years. We believe that this case, like the one previously reported, represents a clinical variant of Hashimoto-Pritzker disease.