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-Langerhans cell histiocytosis, specifically as an early mononuclear variant of juvenile xanthogranuloma (JXG). However, the progression of BCH into JXG in 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 flat plaques over both cheeks, in addition to isolated papules. A punch biopsy of a plaque revealed dermal infiltration by vacuolated and scalloped histiocytes positive for CD68 KP-1, and that lacked expression of CD1a and S-100 protein, favoring macrophages over Langerhans cells. Electron microscopy study showed comma-shaped intracytoplasmic bodies in the histiocytic cells leading to the diagnosis of BCH. One year later, after an episode of varicella-zoster infection, the flat plaques over the cheeks became large reddish-yellow nodules, and in a second biopsy appeared to progress to JXG. Virus-related mechanisms of progression are discussed.