Hereditary Progressive Mucinous Histiocytosis: New Insights Into a Rare Disease.

Hereditary progressive mucinous histiocytosis is a rare, benign, skin-limited form of non-Langerhans cell histiocytosis. We report on a 5-year-old boy who presented in infancy with self-resolving dermal nodules but later developed persistent and progressive erythematous papules on the face and scalp. Histologic evaluation revealed dermal aggregates of S-100/CD1a-negative histiocytes with abundant mucin. We present this case to highlight the evolution of the lesional morphology in infancy and early childhood and to stress the importance of histology in confirming this rare disorder.