Follicular mycosis fungoides. A histopathologic analysis of nine cases

BACKGROUND: The spectrum of mycosis fungoides is exceedingly broad. Many different variants have been described, based on both clinical appearance and histological pattern. A rare form which shows preferential infiltration of hair follicles by malignant lymphocytes is follicular mycosis fungoides. METHODS: We reviewed our experience with nine cases of follicular mycosis fungoides. RESULTS: The unifying feature was infiltration of the hair follicle epithelium by atypical lymphocytes causing varying degrees of damage to the hair follicles. In some specimens the lymphocytes displayed only minor atypia leading to a misinterpretation as pseudolymphoma. Gene rearrangement studies were particularly helpful for establishing a diagnosis of malignant lymphoma. Additionally, epidermotropism of lymphocytes, eosinophils and mucin deposition were present to varying degrees. Mucin makes the distinction from mycosis fungoides-associated follicular mucinosis difficult. We found both dermal mucin and a follicular mucinosis pattern present at different stages of disease in the same patient. CONCLUSIONS: We suggest the term mycosis fungoides-associated follicular mucinosis should be replaced by follicular mycosis fungoides in future lymphoma classification schemes.