Figure 3: Immunohistological features of folliculotropic mycosis fungoides.
(A-B) Superficial and deep dense dermal monotonous lymphocytic infiltrate with predominantly perifollicular/folliculocenteric distribution extending down into the mid-dermis. There is tagging of the lymphocyte along the basal layer of the follicular epithelium, with some lymphocytes enclosed within haloes. There is the attenuation of the epidermis, but there is no atypia or epidermotropism, Pautrier microabscess formation., tagging, haloed lymphocytes, lymphocyte atypia, or pagetoid spread in the spinous layer. The interfollicular epidermis is not involved. (hematoxylin-eosin stain, original magnification, A:x20, and B:x40).
(C-D) Exocytosis of small to medium-sized hyperchromatic lymphocytes into the follicular epithelium of the bulbar and isthmic portions of the hair follicle with disproportionate spongiosis and destruction of the hair follicles. The follicular epithelium is focally spongiotic (hematoxylin-eosin stain, original magnification, C-D: x400).
(E-F) A close-up examination of PAS/Alcian blue stained sections reveals mucin deposition in the hair follicles and the interstitial spaces (PAS/Alcian blue, original magnification, E-F: x400)
(G-H) Dense CD4 positive perifollicular lymphoid aggregates with marked infiltration of the follicular epithelium (folliculotropism) by small to medium-sized T- T-lymphocytes (original magnification, E: x20, and F:x400).
(I): Minimal CD8-positive T- T-lymphocytes are seen. The shift of the CD4 positive folliculotropic T-cells (H) to the CD8 (I) ratio favors the diagnosis of F-MF (original magnification, I:x400). The lack of epidermotropism should not deter dermatopathologists from considering F-MF as a diagnostic possibility.