Progressive nodular histiocytosis: a case report with literature review, and discussion of differential diagnosis and classification.

Histiocytoses are a heterogeneous group of disorders which are difficult to categorize because of overlapping clinical and microscopic features, and incompletely understood mechanisms of cellular origin and triggers of proliferation. Progressive nodular histiocytosis (PNH) is a rare non-Langerhans cell histiocytic (NLH) disorder. We present the case of a 34-year-old woman with PNH, who has involvement of the back, head and neck, face, and uniquely, extensive involvement of the posterior pharynx and larynx, which has shown progressive worsening and deformity over a 7-year course. Clinically it is best classified as PNH, although it microscopically closely resembles juvenile and adult xanthogranulomatosis. This study reinforces the concept that the NLH is a closely related group of disorders, possibly representing a spectrum of a single underlying process.