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Mycosis fungoides

Synonyms: kutanes T-Zell-Lymphom, CTCL

By Dr. Pascal Bafteh · last updated 09/2026

Mycosis fungoides: ill-defined, slightly infiltrated erythematosquamous lesion with fine scaling at the knee, resistant to treatment for months (Photo: Wikindrea, Wikimedia Commons, CC BY-SA 4.0) — Wikindrea, „Mycosis Fungoides Before Sun and Cartamo", CC BY-SA 4.0, via Wikimedia Commons · CC BY-SA 4.0 · Source

Definition & Epidemiology

Mycosis fungoides (MF) = most common cutaneous T-cell lymphoma (CTCL), originating from CD4-positive helper memory T-cells with skin tropism.
Sézary syndrome (SS) = leukemic variant with erythroderma + circulating atypical T-cells + generalized lymphadenopathy.
Incidence of MF ~ 0.5 / 100,000 / year; mostly 50–60 years of age; M:F ≈ 2:1.

Clinical Presentation by Stage

Patch (IA): reddish-brown, non-infiltrated macules with fine lamellar scaling, often on buttocks / trunk
Plaque (IB): infiltrated erythematous plaques, sharply demarcated
Tumor (IIB): exophytic nodules / tumors, often ulcerated
Erythroderma (III): > 80 % BSA, pruritus, "L'homme rouge"
Sézary (IV): + atypical circulating cells, lymphadenopathy

Sézary Syndrome

Triad: Erythroderma + generalized lymphadenopathy + atypical circulating Sézary cells.
Excessive pruritus ("Sézary pruritus") — scratch-induced lichenification.
Folliculotropic variant with alopecia + comedones + mucinosis.

Diagnostics

Histology

Pathognomonic correlate Pautrier microabscesses — intraepidermal CD4+ T-cell aggregates without significant spongiosis.
Epidermotropism of atypical T-cells without spongiosis (DD to eczema).
In advanced stages, dense band-like infiltrate in the upper dermis.

Immunohistochemistry + Clonality

CD3+/CD4+/CD45RO+ T-helper cells, partial CD7 loss.
TCR gene rearrangement PCR (T-cell clonality) — supports diagnosis, not solely diagnostic.

Flow Cytometry (peripheral blood)

Sézary cell phenotype CD4+/CD7−/CD26− — atypical T-cells with CD7 and CD26 loss.
Sézary diagnosis: ≥ 1000 Sézary cells/µl OR CD4:CD8 ratio > 10 OR ≥ 40 % CD4+/CD7 loss.

Tumor Burden Markers

Tumor burden markers LDH + β2-microglobulin — as a surrogate for tumor mass.
Staging: TNMB system (Olsen 2007), mSWAT score (BSA × lesion severity).

Differential diagnoses

Seborrhoeic dermatitis
Atopic dermatitis (atopic eczema)
Folliculitis decalvans
Cutaneous lymphoma
Primary cutaneous diffuse large B-cell lymphoma (NOS)
Primary cutaneous anaplastic large cell lymphoma
Erythroderma (exfoliative dermatitis)
Psoriasis vulgaris (plaque psoriasis)

Practise Mycosis fungoides in the app

Flashcards with spaced repetition, exam questions and spot-the-diagnosis on this topic – in DermaFuchs, free of charge.

In the DermaFuchs app: 7 flashcards · 4 clinical images

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Sources (selection)

AWMF S2k Kutane Lymphome 2021

More skin tumours

Note: This page is intended for medical education and does not replace diagnosis or treatment decisions in individual cases. Treatment and follow-up content is available in the app.