Spontaneous regression of congenital cutaneous histiocytosis X: report of a case with discussion of nosology and pathogenesis.

Spontaneous regression of histiocytosis X is a rare biologic event as judged by the extensive recorded experience in the literature. We present a case of congenital cutaneous histiocytosis X that resolved without specific therapy in the first week of life. Histologic and ultrastructural studies confirmed the interpretation. This child is an example of so-called pure cutaneous histiocytosis, which, like the other unisystem forms of the disorders, has an excellent prognosis.