Follicular Mycosis Fungoides: Variability of a Rare Entity

Abstract

Three patients with follicular mycosis fungoides (FMF), a rare variant of folliculotropic cutaneous T-cell lymphoma, are discussed. Follicular involvement in cutaneous T-cell lymphoma commonly presents clinically with alopecia, follicular cysts, or comedo-like lesions usually associated with follicular mucinosis and strong epidermotropism. In contrast, FMF, in a strict sense, has been defined as a lymphocytic infiltration of hair follicles in the absence of both epidermal invasion and follicular mucin. Case 1 shows a clinically stable form of FMF characterized by circumscribed alopecia and its persistent resistance to topical therapeutic approaches. In contrast, Cases 2 and 3 demonstrate that classic mycosis fungoides lesions and FMF can occur simultaneously and that transitions occur from mycosis fungoides to FMF and vice versa. These observations strengthen the concept that FMF and mycosis fungoides represent just two variants of one entity of cutaneous T-cell lymphoma. In Case 3, rapid progression into tumor-stage mycosis fungoides and the follicular infiltration was controlled with bexarotene. Because it was previously suggested that FMF may have a worse prognosis compared with classic mycosis fungoides, this impressive response to bexarotene is of great clinical interest and may spark new studies employing this novel retinoid for FMF treatment.