Pyoderma gangrenosum

By Dr. Pascal Bafteh · last updated 09/2026

Overview

Pathogenesis & Clinical Features

• Pathogenesis: Pathogenesis involves IL-36 / IL-1β / IFN-γ (neutrophilic inflammation).
• Clinical Presentation: Atypical ulcer with a livid-erythematous border + peripheral pustules, often on the lower leg.
• Pathergy Phenomenon: Classically, wound worsening due to trauma due to surgery / puncture — important for surgical planning!
• Associations: IBD (ulcerative colitis, Crohn's disease) ~30%, RA, hematological neoplasms (MDS, AML, IgA-MGUS), PAPA/PASH spectrum.

Diagnostics (Paracelsus Score)

• 3 Major Criteria (3 pts.): Progressive course, exclusion of other causes (PAD, DM ulcer, CVI, vasculitis), livid border.
• Minor Criteria (1–2 pts.): Ulceration, extreme pain, neutrophil-rich histology, improvement with corticosteroids, pathergy.
• ≥ 10 points → probable PG.
• Spindle biopsy from the border for histology + exclusion of pathogens (caution: pathergy risk!).
• Biopsy Strategy for Suspected PG (Exam Trap!): Due to the pathergy phenomenon, before / parallel to biopsy, initiate systemic steroids — otherwise, wound worsening due to surgical trauma.

Overview

• Women 20–50 years, neutrophilic dermatosis; livid eroded border + pathergy phenomenon + often peristomal (stoma) or post-traumatic.
• Diagnosis: Paracelsus Score / PARACELSUS Score (see card Neutrophilic Dermatoses) — Points for: Major signs + Minor signs + Exclusion of other causes.
• Pathomechanism: neutrophilic inflammation via IL-1β / IL-36.
• Associations: PASH-/PAPASH-Syndrome (Pyoderma + Acne + Hidradenitis ± Pyogenic Arthritis), IBD, Hematological diseases.

Differential diagnoses

• Arterial (ischaemic) ulcer
• Diabetic dermopathy
• Lepromatous leprosy
• Secondary syphilis (lues II)
• Martorell Ulcer
• Venous leg ulcer
• Pyogenic granuloma
• Ecthyma

Sources (selection)

1. Cohen 2007 Sweet syndrome

More inflammatory skin diseases

• Cheilitis granulomatosa (Miescher)
• Erythema annulare centrifugum (EAC)
• Erythema nodosum
• Graft-versus-host disease (GvHD)
• Granuloma annulare
• Cutaneous sarcoidosis
• Lichen planus
• Lichen sclerosus

Note: This page is intended for medical education and does not replace diagnosis or treatment decisions in individual cases. Treatment and follow-up content is available in the app.