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Cutaneous lymphomaCTCL variantICD-10 C84.0 (variant)

Folliculotropic mycosis fungoides

FMF; pilotropic MF; follicular MF

Folliculotropic mycosis fungoides is a distinctive variant of MF in which atypical T cells infiltrate hair follicles rather than the interfollicular epidermis. It accounts for ~10% of MF cases and presents most commonly on the head and neck with follicular papules, alopecic plaques, acneiform lesions, comedones, milia-like cysts and rarely tumour-stage nodules. Compared with classical MF, FMF is less responsive to skin-directed therapy because of the deeper folliculotropic infiltrate; localised radiotherapy is often required. Early-stage FMF behaves similarly to classical early MF but advanced FMF carries a worse prognosis than advanced classical MF of equivalent stage.

CurrentLast reviewed 15 May 2026
Clinical image of Folliculotropic mycosis fungoides
Folliculotropic mycosis fungoides. Image sourced from DermNet New Zealand. Used under CC BY-NC-ND 4.0. No endorsement implied.

Clinical features

  • Predilection for head and neck β€” including eyebrows, scalp, beard area.
  • Follicular papules and plaques, often coalescing into infiltrated indurated plaques with overlying follicular accentuation.
  • Alopecia β€” patchy, with prominent follicular openings or comedone-like cysts; eyebrow loss is highly characteristic.
  • Acneiform / cystic lesions with comedones and milia-like cysts.
  • Tumour-stage nodules in advanced disease.
  • Pruritus typically more severe than classical MF.
  • Median age and sex distribution similar to classical MF; both early- and advanced-onset variants described.

Histology

  • Perifollicular and intrafollicular infiltrate of atypical CD4+ T cells, sparing the interfollicular epidermis.
  • Follicular mucinosis β€” alcian-blue–positive mucin deposition within follicular epithelium β€” is common.
  • Loss of CD7 and CD26 as in classical MF.
  • Folliculotropic infiltrates extend deep into the dermis; biopsy depth must include the entire follicular unit.

Early vs advanced FMF (Hodak/Amitay-Laish)

  • Early-stage FMF β€” limited disease with infiltrates restricted to upper follicular epithelium; prognosis similar to early classical MF.
  • Advanced-stage FMF β€” deeper, denser folliculotropic infiltrates with large-cell transformation and constitutional symptoms; prognosis closer to tumour-stage classical MF.
  • Histopathological depth and density of folliculotropism are prognostically important.

Staging

  • Same ISCL-EORTC TNMB system as classical MF.
  • FMF is treated as a separate prognostic entity at any given stage β€” early-stage FMF generally classified as T2 even if BSA is limited, reflecting the deeper biology.
  • Baseline assessment as for classical MF β€” bloods, LDH, FBC with flow cytometry, lymph-node examination, imaging if advanced.

Management

  • Skin-directed therapy alone is often insufficient because the infiltrate is deep within the follicle.
  • Limited disease β€” localised radiotherapy (8–30 Gy) is highly effective; PUVA + retinoids; topical mechlorethamine; topical bexarotene.
  • Extensive early-stage disease β€” PUVA combined with low-dose oral bexarotene or interferon-Ξ±; consider TSEB.
  • Advanced disease β€” manage as advanced MF: bexarotene, brentuximab vedotin (if CD30+, TA577), mogamulizumab (TA754), allogeneic stem-cell transplantation in selected younger patients.
  • Supportive β€” antibiotics for staphylococcal superinfection (common in alopecic plaques), pruritus management, psychological support for visible alopecia.

Prognosis and pitfalls

  • Early-stage FMF (Hodak/Amitay-Laish type 1) β€” 10-year DSS approaching classical early MF.
  • Advanced-stage FMF β€” 10-year DSS 25–50%, closer to tumour-stage classical MF.
  • Diagnostic pitfall β€” early FMF often misdiagnosed for years as alopecia areata, acne, rosacea, atopic dermatitis or seborrhoeic dermatitis; threshold for biopsy of refractory facial dermatoses should be low, particularly if accompanied by eyebrow loss or comedonal change.

References

  1. Hodak E, Amitay-Laish I. Folliculotropic mycosis fungoides: clinical-pathological subgroups and prognostic implications. Br J Dermatol; 2014;171:495–504.
  2. Willemze R et al. WHO-EORTC classification update. Blood; 2019;133:1703–14.
  3. Gilson D et al. British Association of Dermatologists and U.K. Cutaneous Lymphoma Group guidelines for the management of primary cutaneous lymphomas 2018. Br J Dermatol; 2019;180:496–526.

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