# Paraneoplastic Erythroderma: An Unprecedented Initial Manifestation of In Situ Follicular Neoplasia

## TL;DR

A rare case links in situ follicular neoplasia to severe skin inflammation, suggesting a new understanding of this typically silent condition.

## Contribution

First reported case linking in situ follicular neoplasia to paraneoplastic erythroderma.

## Key findings

- Complete resolution of erythroderma after excision of ISFN-positive lymph nodes.
- ISFN may not be biologically inert as previously thought.

## Abstract

Paraneoplastic erythroderma is a severe cutaneous reaction characterized by diffuse erythema and scaling of the body surface area. While typically associated with hematologic malignancies such as cutaneous T-cell lymphoma or solid tumors, it is notoriously refractory to standard dermatologic therapies. In situ follicular neoplasia (ISFN) is generally regarded as an indolent, clinically silent condition discovered incidentally. We present a unique case of severe, treatment-resistant erythroderma in an elderly male, which resolved completely following the excision of lymph nodes positive for ISFN. To our knowledge, this is the first reported association between ISFN and paraneoplastic erythroderma, challenging the paradigm that ISFN is a biologically inert entity.