Five years of ‘eczema’ that won’t clear

Mycosis fungoides, patch-stage, T2 N0 M0 B0 — ISCL/EORTC stage IB — managed at a UK supraregional cutaneous lymphoma service

Learning points

• Mycosis fungoides typically presents on sun-protected sites (buttocks, inner thighs, breasts, lower abdomen) — a useful clinical clue.
• Diagnostic delay of 4–6 years is typical; patients are frequently treated as eczema or psoriasis. A non-responsive 'eczematous' dermatitis in an adult warrants biopsy.
• Repeat biopsy is the rule, not the exception — the first biopsy is non-diagnostic in 30–50% of cases. Take multiple deep (≥ 4 mm) punches from indurated areas, ideally after a 2–4 week wash-out of topical steroid which can suppress the infiltrate.
• Diagnostic findings: epidermotropic infiltrate of atypical lymphocytes with cerebriform nuclei, Pautrier microabscesses (intraepidermal collections). IHC: CD2+ CD3+ CD4+ CD45RO+, frequent loss of CD7 and CD26. PCR for T-cell receptor (TCR) clonality — the same clone across separate biopsies supports CTCL.
• Staging is by ISCL/EORTC TNMB: T (skin), N (nodes), M (visceral), B (peripheral blood Sézary cells). Body surface area drives T-stage (T1 < 10%, T2 ≥ 10% patches/plaques, T3 tumours, T4 erythroderma).
• Patch / plaque mycosis fungoides (stages IA–IIA) is indolent with normal life expectancy on skin-directed therapy.
• UK supraregional cutaneous lymphoma services co-ordinate care; PUVA / nbUVB, topical mechlorethamine, potent topical steroids, and (for advanced stages) brentuximab vedotin, mogamulizumab, total skin electron beam therapy and extracorporeal photopheresis.