AKT · Dermatology/Wounds, ulcers & burnslow yield

Pyoderma gangrenosum

Neutrophilic dermatosis (often immune-mediated, systemic associations)

Overview

A rare, painful, ulcerating neutrophilic dermatosis — NOT an infection despite the name. A rapidly enlarging ulcer with a characteristic violaceous, undermined, overhanging border, classically on the legs. Strongly associated with IBD, inflammatory arthritis and haematological disease, and it Koebnerises — so debriding/operating on it makes it worse.

Recognise

Starts as a pustule/nodule that breaks down into a rapidly enlarging, very PAINFUL ulcer
Characteristic violaceous (purple), undermined, overhanging border with a necrotic/boggy base
PATHERGY — new lesions provoked by trauma (including surgery/debridement); associations: inflammatory bowel disease, rheumatoid/seronegative arthritis, haematological malignancy

Red flags

Misdiagnosis as infection leading to debridement/surgery WORSENS it (pathergy); rapid progression and severe pain

Differentials & how to tell them apart

Infective ulcer / necrotising fasciitisthe crucial distinction — PG is sterile and worsened by surgery, whereas necrotising infection needs urgent debridement; wrong call is dangerous either way

Venous/arterial ulcertypical site/features and vascular assessment — PG has a violaceous undermined border and rapid painful growth

Vasculitic ulcervasculitis screen, biopsy

Squamous cell carcinoma (Marjolin)chronic ulcer with heaped edges — biopsy

Clinical image

We can't host this one — the image is DermNet's and their licence doesn't cover us republishing it. Their page for it is free to view.

Pyoderma gangrenosum — clinical imagesDermNet

Investigations

A diagnosis of EXCLUSION (no specific test) — biopsy shows a neutrophilic infiltrate and helps exclude infection/vasculitis/malignancy. Screen for associations: IBD work-up, FBC/blood film, autoimmune and paraprotein screen.

Management

Systemic corticosteroids (or ciclosporin) + treat associations; AVOID surgical debridement

1Recognise it (exclude infection/vasculitis/malignancy by biopsy) and treat the inflammation — systemic corticosteroids or ciclosporin — plus gentle, non-traumatic wound care.Gate: Do NOT debride or surgically manage pyoderma gangrenosum — it exhibits PATHERGY, so trauma/surgery makes it dramatically worse; the instinct to treat an "infected ulcer" surgically is the classic trap
2Refractory or IBD-associated disease → biologics (anti-TNF such as infliximab); always investigate and treat the underlying association (IBD, arthritis, haematological disease).

Systemic corticosteroids — first-line to control the inflammation

Ciclosporin — alternative/adjunct first-line immunosuppressant

Biologics (anti-TNF, e.g. infliximab) — refractory disease or with associated IBD

Gentle wound care; treat the associated disease; AVOID debridement — do not surgically debride (pathergy)

Key points

Two exam pearls: it is a neutrophilic dermatosis (not infective), and pathergy means you must NOT debride it. The violaceous undermined border + IBD association is the recognition pattern.

Monitor & prognosis

Ulcer response, the associated systemic disease, immunosuppression.

Heals with immunosuppression (often with cribriform scarring); can recur, especially if the association is active.

Source: DermNet; BAD/StatPearls