[Disseminated juvenile xanthogranuloma expressing protein S100].

BACKGROUND: Juvenile xanthogranuloma (JXG) is a form of self-healing non-Langerhans histiocytosis. We report a new case of disseminated JXG without visceral involvement but with positive immunostaining of the majority of histiocytes for protein S100. PATIENTS AND METHODS: A 6-month-old male infant was admitted to our department in January 2010 for congenital nodular lesions of varying size, shape and appearance. The remainder of the dermatological and physical examination was unremarkable. The diagnosis of disseminated JXG, strongly suggested clinically, was confirmed by a skin biopsy. However, immunohistochemistry was confusing, with positivity for protein S100. The lesions regressed spontaneously. DISCUSSION: The aim of this case report is to highlight the lack of any forced association between alarming skin lesions of eruptive JXG and systemic involvement. The distinguishing feature of our case is the positive immunostaining for protein S100 in the histological section, which although rare in XJG, does not cast doubt on the diagnosis of non-Langerhans histiocytosis providing the clinical presentation is typical. Therapeutic abstention is the rule.