Follicular Mycosis Fungoides Mimicking a Cutaneous B-Cell Lymphoproliferative Disorder

The document described a case of follicular mycosis fungoides (MF), an uncommon variant of MF, in a patient with rapidly progressing lesions on the face and typical MF lesions elsewhere. The histology showed dense lymphoid infiltrates with folliculotropism and epidermotropism, and a prominent B-cell component, initially leading to a misdiagnosis of cutaneous B-cell lymphoma. The correct diagnosis of follicular MF was confirmed through clonal T-cell receptor gene arrangements and the absence of clonality for heavy chain gene rearrangements. This case highlighted the rapid progression of this MF variant and the diagnostic challenges it presents, as it can mimic a B-cell proliferative disorder.