Background: In the course of mycosis fungoides, pilofollicular manifestations without mucinosis (papules, keratoses, comedones, or epidermal cysts) are rare (15 cases reported). Therefore, histological and clinical diagnoses may be difficult. The clinical course and histopathological and immunohistochemical findings in 9 patients are described.
Observations: Pilofollicular lesions were present at the onset (n = 3), before (n = 3), or during a relapse of mycosis fungoides (n = 3). Comedones and epidermal cysts were most frequent (n = 5). They disappeared with lymphoma therapy (n = 4), therapy with isotretinoin (n = 3), or spontaneously (n = 1), or they persisted (n = 1). Clues to the histopathological diagnosis consisted of pilotropism of the infiltrate with minor alteration of the hair follicle walls. The infiltrate was monomorphous and composed of sezariform CD4+ lymphocytes. Pilotropic or peripilofollicular infiltrates, or the absence of infiltrate, were detected in consecutive biopsy specimens obtained from the same patient. The keratinocyte expression of intercellular adhesion molecule type 1 was observed in the hair follicle bulb in front of the pilotropic infiltrate but not in the epidermis. No staining was observed in biopsy specimens of 6 of 7 patients with follicular mucinosis, of folliculitis lesions, or of normal hair follicles.
Conclusions: Our findings indicate the role of adhesion molecules in pilotropism leading to mechanical obstruction of the follicle by tumoral cells followed by hyperkeratosis and cyst formation. It remains to be determined if the expression of intercellular adhesion molecule type 1 is the cause or the consequence of pilotropism. By becoming more aware of it, this variant of mycosis fungoides is probably not so rare.