# Pyoderma Gangrenosum Mimicking Necrotizing Fasciitis: A Case Report

## TL;DR

A case of pyoderma gangrenosum was initially misdiagnosed as necrotizing fasciitis, highlighting the importance of careful clinical evaluation to avoid unnecessary surgery.

## Contribution

This case report emphasizes the diagnostic challenges of pyoderma gangrenosum mimicking necrotizing fasciitis and highlights key clinical clues for accurate diagnosis.

## Key findings

- Pyoderma gangrenosum was diagnosed after ruling out infection through negative cultures and observing characteristic pustules.
- Treatment with prednisolone and adalimumab led to rapid symptom resolution and no relapse.
- Clinical assessment of skin lesions and fat necrosis can prevent unnecessary surgical interventions in atypical cases.

## Abstract

Pyoderma gangrenosum (PG) is a rare neutrophilic dermatosis that can mimic other severe conditions, complicating diagnosis. We report a case of PG of the knee initially mistaken for necrotizing fasciitis (NF) in a 68-year-old woman who presented with knee swelling, erythema, papules, and pustules following a fall. Despite antibiotic therapy and surgical debridement for suspected NF, the patient’s fever persisted, and laboratory markers (elevated WBC and C-reactive protein) did not improve. Histopathology revealed a dense neutrophilic infiltrate, and negative cultures ruled out infection, leading to a PG diagnosis. Treatment with oral prednisolone (60 mg/day) rapidly resolved symptoms, followed by negative pressure wound therapy, skin grafting, and adalimumab initiation. The patient stabilized without relapse. Key diagnostic clues included abundant pustules, characteristic of pustular PG, and the absence of fat tissue necrosis during surgery. This case highlights the diagnostic challenge of distinguishing PG from NF, as both may involve deep tissue inflammation. While histopathology and cultures are critical, results are delayed, necessitating reliance on clinical observations. Careful assessment of skin lesions and evaluation of fat necrosis (finger test) can prevent unnecessary surgical interventions, emphasizing the importance of considering PG in atypical presentations of suspected NF.