# Reactive Granulomatous Dermatitis: A Descriptive Study of 10 Patients

## TL;DR

This study describes 10 cases of reactive granulomatous dermatitis and its links to autoimmune diseases, cancer, and TNF inhibitors.

## Contribution

The study provides a detailed case series highlighting the associations of RGD with autoimmune diseases and malignancy.

## Key findings

- 7 out of 10 patients had an autoimmune disease at diagnosis, including inflammatory arthritis or bowel disease.
- One patient with idiopathic RGD developed high-grade B-cell lymphoma 6 months later.
- Two patients showed a possible link to TNF inhibitors.

## Abstract

Reactive granulomatous dermatitis (RGD) is a rare and misunderstood skin disorder. It includes interstitial granulomatous dermatitis and palisaded neutrophilic and granulomatous dermatitis: 2 entities of the same spectrum. Multiple associations are described with RGD in the literature, including autoimmune diseases, malignancy, and drugs.

To report and describe the suspected associations with RGD at the time of diagnosis and in the following year.

We retrieved and described cases of RGD confirmed by skin biopsy and clinicopathologic correlation. All patients were evaluated in the Centre Hospitalier Universitaire de Québec—Université Laval between January 2000 and December 2020. Collected data include the systemic diseases (autoimmune disease, malignancy) and suspected drugs, in addition to the clinical presentation and prescribed treatments.

Out of the 10 patients with RGD, 7 patients were known to have an autoimmune disease at the time of diagnosis. They either had inflammatory arthritis (3/10) or inflammatory bowel disease (4/10). There was a clinical suspicion of a possible association with a tumor necrosis factor (TNF) inhibitor in 2 of these 7 patients. Among the 3 patients with idiopathic RGD at the time of diagnosis, 1 patient developed a high-grade B-cell lymphoma 6 months later. There was no new association identified in the following year for patients with a known autoimmune condition.

This descriptive study supports RGD and its previously described systemic associations, particularly autoimmune diseases, malignancy, and certain drugs (specifically TNF inhibitors). The majority of patients already had one of these associations identified at the time of histopathological diagnosis.