Juvenile xanthogranuloma.

Juvenile xanthogranuloma (JXG) is a benign, self-healing disorder characterized by solitary or multiple yellow-red nodules on the skin and, occasionally, in other organs. It is predominantly a disease of infancy or early childhood, although adults may also be affected. Histologically, JXG represents an accumulation of histiocytes lacking Birbeck granules (non-Langerhans cells), which can be differentiated from Langerhans cells by specific staining techniques. Affected persons have normal lipid metabolism. JXG is therefore classified as a normolipemic non-Langerhans cell histiocytosis. The patient's general health is not impaired and, in the absence of associated conditions, the prognosis is excellent. Diagnosis is readily made in typical cases, but may be more difficult in unusual variants.