The clinical features and histopathologic patterns of folliculotropic mycosis fungoides in a series of 38 cases

Background The recognition of folliculotropic mycosis fungoides ( FMF ) may pose diagnostic challenges, owing to the variety of histopathological findings. Objective In this study, our aim is to describe the broad spectrum of the histopathological patterns in a total of 86 biopsies from 38 patients with FMF , together with the clinical features. Results The most frequent histopathologic pattern was the folliculocentric/folliculotropic pattern, with or without follicular mucinosis. Keratin‐filled cysts and comedones were the second most common pattern in the biopsies. Other less common findings included widening of the hair follicle orifis with keratotic plugging, reminiscent of keratosis pilaris, granuloma formation, eosinophilic or suppurative folliculitis and basaloid folliculolymphoid hyperplasia. Coexisting syringotropism was present in some biopsies. The CD4 : CD8 ratio was at least 4 : 1 or more in most biopsies. Grouped follicular papules and patch/plaque lesions with follicular prominence were the most frequent clinical findings. Folliculocentric lesions such as milia, cysts and acneiform lesions, alopecia, loss of hair or eyebrows were also seen. In 6 out of 38 (15.8%) patients, transformation to large‐cell lymphoma was observed during the follow‐up. Conclusion The awareness and the identification of the various histopathological presentations of FMF by pathologists, as well as by clinicians, are imperative to prevent diagnostic errors.