Benign cephalic histiocytosis progressing into juvenile xanthogranuloma - A non-Langerhans cell histiocytosis transforming under the influence of a virus?

Benign cephalic histiocytosis (BCH) is best understood as a form of non-lan gerhans cell histiocytosis, specifically as an early mononuclear variant of juvenile xanthogranuloma (JXG). However, the progression of BCH into JXG i n the same patient has only been reported once before. We describe the case of a 2-year-old girl with asymptomatic, large, ill-defined infiltrated fla t plaques over both cheeks, in addition to isolated papules. A punch biopsy of a plaque revealed dermal infiltration by vacuolated and scalloped histi ocytes positive for CD68 KP-1, and that lacked expression of CD1a and S-100 protein, favoring macrophages over Langerhans cells. Electron microscopy s tudy showed comma-shaped intracytoplasmic bodies in the histiocytic cells l eading to the diagnosis of BCH. One year later, after an episode of varicel la-zoster infection, the flat plaques over the cheeks became large reddish- yellow nodules, and in a second biopsy appeared to progress to JXG. Virus-r elated mechanisms of progression are discussed.