The Spectrum of Histopathologic and Immunohistochemical Findings in Folliculotropic Mycosis Fungoides

Abstract

Since the original designation of folliculotropic mycosis fungoides (FMF) as a distinct entity, there has been an increasing appreciation of the broad clinical and histopathologic spectrum with which this disease can present. However, there have been few large histologic studies characterizing the various histopathologic patterns. In this study, we attempt to describe the histopathologic and immunohistochemical features of 47 biopsy specimens from 34 patients with FMF. We searched our lymphoma database for patients with FMF in which detailed histopathologic information and slides as well as clinical information was available for review. Additionally, immunohistochemical studies for CD4, CD8, and CD1a were performed in all cases in which the block was available. In addition to the prototypical pattern of a folliculotropic lypmphoid infiltrate with or without mucinosis, the histologic features of follicular mycosis fungoides may include a granulomatous reaction, cystic and comedonal changes, an eosinophilic folliculitis pattern and basaloid folliculolymphoid hyperplasia as well as pustular changes, interface dermatitis and an interstitial dermatitislike pattern. Unlike conventional mycosis fungoides, eosinophils and plasma cells are conspicuous within the accompanying reactive infiltrate. We have also noted an exceedingly high number of Langerhans cells within the follicular epithelium. The CD4:CD8 ratio frequently is 10:1 or greater and the follicles show abundant CD1a positive cells. FMF may present with a broad spectrum of histopathologic changes including interstitial, granulomatous, fibrotic and acneiform reactions that may lack the typical histologic attributes of a cutaneous T-cell lymphoma. Recognition of these myriad of histologic presentations can be of great diagnostic utility.