A Case of Folliculotropic Mycosis Fungoides Initially Misleading as a Poikilodermatous Rash - The Importance of Gene Rearrangement Testing in Early-Stage Disease

Sep 30, 2026

Folliculotropic mycosis fungoides (FMF) is a distinct and often aggressive variant of cutaneous T-cell lymphoma that can mimic benign dermatoses in early disease. A 42-year-old man presented with a chronic, progressively worsening, intensely pruritic, scaly eruption of the lower back, buttocks, and proximal extremities. After topical corticosteroids failed, serial biopsies showed atypical perivascular and perifollicular lymphoid infiltrates. Clonal T-cell receptor gene rearrangement testing supported early-stage folliculotropic mycosis fungoides. Treatment began with narrowband ultraviolet B phototherapy three times weekly alongside topical corticosteroids and close follow-up.

LanguageEnglish

CategoryHealthcare

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Reading Time18 min

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Abstract

Introduction

Diagnostic workup in early-stage mycosis fungoides

Role of TCR gene rearrangement testing

Immunophenotyping and diagnostic accuracy

Early-stage management considerations

Received 10/25/2025 Review began 11/06/2025 Review ended 12/08/2025 Published 12/08/2025 © Copyright 2025 Moreno et al. This is an open access article distributed under the terms of the Creative Commons Attribution License CC-BY 4.0. , which permits unrestricted use , distribution , and reproduction in any medium , provided the original author and source are credited. DOI: 10.7759/cureus.98736 Open Access Case Report Published via Lake Erie College of Osteopathic Medicine (LECOM) A Case ofFolliculotropic Mycosis Fungoides Initially Misleading as a Poikilodermatous Rash: The Importance of Gene Rearrangement Testing in Early-Stage Disease (Folliculotropic T-Cell Lymphocytosis) Brian A. Moreno 1 , Moises Lutwak 2, Samantha Sherkin 2 , Francisco Kerdel 3 1. Dermatology, Lake Erie College of Osteopathic Medicine, Bradenton, USA 2. Dermatology, Larkin Community Hospital, South Miami, USA 3. Dermatology, Florida Academic Dermatology Center, Coral Gables, USA Corresponding author: Brian A. Moreno, [bmoreno96med@gmail.com](bmoreno96med@gmail.com) Abstract Folliculotropic mycosis fungoides (FMF) is a distinct and often aggressive variant of cutaneous T-cell lymphoma (CTCL) that can mimic benign dermatoses, particularly in its early stages. We present the case of a 42-year-old man with a chronic, progressively worsening, intensely pruritic, scaly eruption involving the lower back, buttocks, and proximal extremities. Despite initial management with topical corticosteroids, his condition persisted and evolved into poikilodermatous patches with follicular accentuation and hyperpigmented plaques, prompting further evaluation. Serial skin biopsies from the left anterior distal thigh, right posterior shoulder, and right inferior medial lower back revealed superficial and deep perivascular and perifollicular atypical lymphoid infiltrates. Molecular studies demonstrated clonal T-cell receptor (TCR) gene rearrangement, raising concern for early-stage cutaneous T-cell lymphoma with folliculotropic involvement. Given the clinical presentation and histopathologic findings, a diagnosis of early-stage folliculotropic mycosis fungoides was made. The patient was initiated on narrowband ultraviolet B (nbUVB) phototherapy three times per week in addition to topical corticosteroids, with close clinical follow-up. Categories: Pathology, Oncology, Dermatology Keywords: adult dermatology, case report dermatology, clinical dermatology, complex medical dermatology, dermatology care, dermatology consult, dermatology oncology, general dermatology, medical dermatology, skin disease/dermatology Introduction Mycosis fungoides (MF) is the most common form of cutaneous T-cell lymphoma (CTCL), characterized by an indolent but persistent malignant T-cell proliferation that often mimics benign dermatoses in its early stages. Folliculotropic mycosis fungoides (FMF) is a recognized clinicopathologic variant with a distinct prognosis, defined by preferential infiltration of neoplastic T cells into hair follicles and a tendency to present with follicular papules, plaques, or alopecia rather than classic MF patches. Because FMF frequently exhibits atypical or misleading morphologies, including poikilodermatous changes, early diagnosis can be challenging. This case highlights how the patient’s misleading clinical presentation ultimately required Tcell receptor (TCR) gene rearrangement testing to confirm clonality and establish an early diagnosis of FMF. The diagnostic workup of early-stage MF can be challenging due to its broad clinical variability and overlapping histopathologic features with benign inflammatory dermatoses. In cases where histology is indeterminate, polymerase chain reaction (PCR)-based TCR clonality assays offer a valuable adjunct for detecting malignant lymphocyte populations. Studies evaluating TCRβ gene rearrangement have demonstrated its utility in confirming clonality in MF, especially when combined with appropria

FAQs

Why can folliculotropic mycosis fungoides be misdiagnosed early?

FMF can mimic benign dermatoses, including misleading poikilodermatous morphologies, especially at early stages. This overlap makes clinical recognition difficult.

What did serial skin biopsies and molecular testing show in this case?

Biopsies revealed superficial and deep perivascular and perifollicular atypical lymphoid infiltrates. Molecular studies demonstrated clonal T-cell receptor (TCR) gene rearrangement, supporting early-stage disease.

How was the patient treated after the diagnosis?

The patient started narrowband ultraviolet B (nbUVB) phototherapy three times per week in addition to topical corticosteroids, with close clinical follow-up.

Sep 30, 2026

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