# Mycosis Fungoides and Cutaneous T-Cell Lymphoma

> Mycosis fungoides and cutaneous T-cell lymphoma for NEET-PG Medicine, covering patch, plaque and tumour stages, Sezary syndrome and skin-directed therapy.

- Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/mycosis-fungoides-and-cutaneous-t-cell-lymphoma
- Exam / course: NEET-PG · Subject: Medicine
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-14
- Last updated: 2026-10-14
- Reference basis: Harrison's Principles of Internal Medicine; Andrews' Diseases of the Skin
- How to cite: "Mycosis Fungoides and Cutaneous T-Cell Lymphoma", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/mycosis-fungoides-and-cutaneous-t-cell-lymphoma

## Direct answer

Mycosis fungoides is the commonest cutaneous T-cell lymphoma, a malignancy of skin-homing CD4-positive T cells that usually begins as a scaly patch. It moves through patch, plaque and tumour stages and can progress to erythroderma with blood involvement, called Sezary syndrome. Early disease is managed with skin-directed therapy, and advanced or refractory disease needs systemic agents.

## What you must remember

- **Phenotype:** CD4-positive mature T cells with skin-homing markers; loss of CD7 is common on flow cytometry.
- **Pautrier microabscesses:** clusters of atypical lymphocytes within the epidermis, the classic histological clue to mycosis fungoides.
- **Early stage:** patches and plaques are staged IA or IB, depending on whether lesions cover less than or at least about 10 per cent of body surface area.
- **Sezary syndrome:** erythroderma with circulating Sezary cells, defined by a count of at least 1000 per microlitre under the ISCL and EORTC criteria.
- **Staging system:** TNMB grades skin (T), lymph nodes (N), visceral disease (M) and blood (B), and sets the treatment intensity.
- **First-line skin therapy:** topical corticosteroids, topical mechlorethamine, narrowband UVB or PUVA; total skin electron beam for extensive disease.
- **Systemic options:** bexarotene, romidepsin, vorinostat, methotrexate and interferon, with mogamulizumab used particularly in Sezary syndrome.

## A stage-directed pathway from patch to Sezary syndrome

Mycosis fungoides is often misdiagnosed for years because early lesions mimic chronic eczema or psoriasis. The diagnosis rests on a sequence of biopsy, immunophenotype, clonality and staging, and each step narrows the next decision.

1. **Biopsy the right lesion.** A plaque or tumour gives a more specific histology than a long-standing patch, which often looks nonspecific.
2. **Read the epidermis.** Atypical lymphocytes with cerebriform nuclei infiltrate the epidermis, forming Pautrier microabscesses in a CD4-positive pattern.
3. **Prove clonality.** T-cell receptor gene rearrangement shows a clonal population and supports the diagnosis when histology is equivocal.
4. **Stage with TNMB.** Skin extent, node size and histology, visceral spread and the blood Sezary cell count together assign the stage.
5. **Start skin-directed therapy.** Topical corticosteroids, topical mechlorethamine and phototherapy cover early stages, and total skin electron beam treats extensive disease.
6. **Escalate for advanced disease.** Systemic agents are reserved for tumour stage, Sezary syndrome or disease that fails skin-directed treatment.

## Where the exam tries to catch you

Questions test whether the skin findings are read as a stage, not just as a rash.

- **Trap:** A scaly patch that persists despite steroid creams is treated as eczema for months. **Correct:** a persistent patch unresponsive to topical steroids needs biopsy, and repeat biopsy is often required because early histology is nonspecific.
- **Trap:** Sezary syndrome is staged by erythroderma alone. **Correct:** the blood Sezary cell count and nodal status define the B and N components, so the count must be measured.
- **Trap:** Pautrier microabscesses are read as spongiotic dermatitis. **Correct:** they are intraepidermal clusters of atypical lymphocytes and point to a lymphoma diagnosis.

## Frequently asked questions

### Which histological feature is characteristic of mycosis fungoides?

Pautrier microabscesses, which are intraepidermal clusters of atypical lymphocytes, are the classic histological feature of mycosis fungoides. They are interpreted together with a CD4-positive phenotype and clonal T-cell receptor rearrangement.

### What defines Sezary syndrome in cutaneous T-cell lymphoma?

Sezary syndrome is erythroderma with a circulating count of at least 1000 Sezary cells per microlitre, under the ISCL and EORTC criteria. Flow cytometry of the blood confirms the abnormal clonal T-cell population.

### Which therapy is first line for early-stage mycosis fungoides?

Early-stage mycosis fungoides is treated first with skin-directed therapy, such as topical corticosteroids, topical mechlorethamine, narrowband UVB or PUVA. Systemic therapy is reserved for advanced or refractory mycosis fungoides.

### How does TNMB staging apply to mycosis fungoides?

TNMB assesses skin involvement (T), lymph node status (N), visceral disease (M) and blood involvement (B) in mycosis fungoides. Patches and plaques form the early stage, while tumours, erythroderma and nodal or visceral spread define advanced disease.

### Which drugs treat advanced cutaneous T-cell lymphoma?

Bexarotene, romidepsin, vorinostat, methotrexate and interferon are systemic options for advanced or refractory cutaneous T-cell lymphoma. Mogamulizumab, an anti-CCR4 antibody, is used particularly in Sezary syndrome.