Congenital solitary histiocytoma: a variant of Hashimoto-Pritzker histiocytosis. A retrospective study of 8 cases.

BACKGROUND: Self-healing solitary-lesion Hashimoto-Pritzker histiocytosis (HPH), a rare, congenital, purely cutaneous Langerhans histiocytosis (only 30 cases reported), carries a good prognosis.

OBJECTIVE: To describe the clinical and histopathological characteristics of solitary HPH.

METHODS: To conduct a retrospective, observational study on 8 affected newborns.

RESULTS: For these infants, with otherwise normal physical examinations, the unique nodule or papule (5-15-mm diameter) was congenital. Systematic routine histological examination of the lesions found dermal infiltrates constituted predominantly of histiocytes with lymphocytes and eosinophils. Protein S100 and CD1a immunolabelings, done for 7 patients, were positive. Electron microscopy (n = 4) observed Birbeck granules. No visceral involvement or recurrence has ever been observed after 2-12 years of follow-up.

CONCLUSIONS: Because of its self-healing nature, congenital solitary HPH frequency has probably been underestimated. In the absence of systemic involvement, regular physical examination for at least 2 years seems a valid approach.