Folliculotropic mycosis fungoides associated with follicular mucinosis: A case report and mini review

Key Clinical Message F‐MF is a rare non‐classic variant of MF. In the case of hair loss, this should be a diagnostic consideration. The essence of the diagnosis of F‐MF is a careful medical history, physical examination, and a combination of immunohistological and molecular analyses (Cureus. 2022; 14:e21231, Ann Saudi Med. 2012; 32:283, Oman Med J. 2012; 27:134, Int J Dermatol. 2016; 55:1396, Saudi Med J. 2018; 39:994 and Case Rep Oncol. 2018; 11:436). Mycosis fungoides (MF) is a primary cutaneous T‐cell lymphoma with multiple subtypes. Follicular MF (F‐MF) is a non‐classic variant of MF. Histological features entail folliculotropism and damage of the epithelium lining of the hair follicles with or without mucin deposition. A 52‐year‐old male patient complained of recurrent skin lesions on the scalp over 8 months. The lesions appeared suddenly, enlarged over time, and became itchy. A skin punch biopsy was performed. Histological features included mucin deposits in the epithelium of the hair follicles and dense, predominantly perifollicular atypical lymphocytes infiltrating the follicular epithelium. The lymphoid cells were composed of CD3‐positive T cells (CD4/CD8‐positive T cells) with a shift in favor of the former. The case was diagnosed as F‐MF on an immunohistological basis. The diagnosis of F‐MF is often difficult for dermatologists and dermatopathologists alike. Not only clinicopathological correlations but also immunohistochemical and molecular analysis are required. Histological features of follicular mycosis fungoides. (A‐B) Dense superficial and deep dermal lymphocytic infiltrate with a predominantly perifollicular/folliculocentric distribution extending into the mid‐dermis. Atypical lymphocytes are located along the basal cell layer of the hair follicle epithelium. Some neoplastic lymphocytes are surrounded by a halo. Although there is epidermal thinning, there is no atypia or epidermotropism, or Pautrier microabscesses. The interfollicular epidermis is not involved. (Hematoxylin and eosin staining, original magnification, A:x20, B:x40). (C‐D) Exocytosis of small and 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. The sebaceous epithelium is also infiltrated by the atypical lymphocytes (hematoxylin‐eosin stain, original magnification, C: x200, D: x