Clinical features and variants

Rapidly enlarging painful ulcer with a violaceous undermined border and necrotic base; surrounding erythema.
Pathergy — new lesions or worsening of existing lesions after surgical / minor trauma (positive in ~ 25–50%).
Four clinical variants:
- Classic (ulcerative) — pretibial; deep painful ulcer; associated with IBD, RA, monoclonal gammopathy.
- Bullous (atypical) — superficial bullae and erosions; dorsal hands, extensor arms, face; strong haematological-malignancy association (AML, MDS, leukaemia cutis differential).
- Vegetative — superficial, less painful, granulomatous; usually no systemic association.
- Peristomal — around stoma sites in IBD; difficult to manage.
Pustular PG — pustules without ulceration; precedes classic PG in some, particularly IBD.

Pathergy — the surgical trap

Pathergy — worsening or new PG lesions after surgical trauma (biopsy, debridement, surgical excision).
Following a clinically-clean WLE, what appears to be post-operative wound infection / dehiscence / necrotising fasciitis may be PG.
Critical pitfall: aggressive surgical debridement worsens PG, expands the wound and may cause limb-threatening deterioration.
Clues — wound expansion out of proportion to surgical defect; violaceous undermined border; severe pain; negative tissue cultures; failure to respond to broad-spectrum antibiotics; rapid onset 24–72 hours post-op.
Suspect PG if a non-healing post-operative wound deteriorates without microbiological evidence of infection and is exquisitely painful — start oral / IV corticosteroids and refer to dermatology urgently.

Diagnosis of exclusion — no specific test; histology is supportive but not pathognomonic.
Several frameworks exist as distinct instruments:
- Maverakis 2018 Delphi consensus criteria (JAMA Dermatol) — one major criterion (exclusion of relevant differentials) + a combination of minor criteria including rapid progression, pathergy, suggestive history, characteristic clinical features, response to immunosuppression.
- PARACELSUS score (Jockenhöfer 2019, Br J Dermatol) — a separate point-based scoring system.
- Su 2004 criteria — the older diagnostic framework.
Histology — dense neutrophilic infiltrate with overlying ulceration, often with leukocytoclastic vasculitis and necrosis. Biopsy from the edge of the ulcer (not the base) — and accept the pathergy risk by combining biopsy with concurrent immunosuppression.
Exclude differentials: bacterial / atypical mycobacterial / fungal infection (deep cultures, AFB, fungal), vasculitis (ANCA, complement), Behçet, antiphospholipid syndrome, calciphylaxis, venous / arterial / mixed ulcer, factitious disease.

Inflammatory bowel disease — Crohn disease, ulcerative colitis. PG is uncommon among IBD patients overall (about 1–3%, cohort-dependent), but IBD is a common associated condition among people who present with PG.
Rheumatoid arthritis and seronegative spondyloarthropathies.
Monoclonal IgA gammopathy — particularly with classic ulcerative PG.
Haematological malignancy — AML, MDS, CMML — particularly bullous PG variant. PG can precede the haematological diagnosis by months.
Solid tumours (rare) — colorectal, breast.
Workup — FBC + film, U&E, LFT, CRP, immunoglobulins + electrophoresis, ANA, ANCA, IBD screen, haematology if cytopenia or bullous PG.

Limited disease — superpotent topical clobetasol propionate, intralesional triamcinolone, topical tacrolimus.
Moderate-severe disease:
- Oral prednisolone 0.5–1 mg/kg/day, tapered over months.
- Ciclosporin 3–5 mg/kg/day (steroid-sparing, can be primary therapy).
- Tumour-necrosis-factor (TNF) inhibitors — infliximab or adalimumab; particularly useful for IBD-associated PG, with IBD commissioning routes such as Crohn's disease TA187 / ulcerative colitis TA329 where the underlying bowel indication is met. PG-specific use is otherwise off-label / specialist-commissioned.
- IL-23 inhibitors (ustekinumab, guselkumab) — emerging evidence.
- Dapsone, sulfasalazine, mycophenolate mofetil in steroid-sparing regimens.
Wound care — non-adherent dressings, atraumatic, no surgical debridement.
Analgesia — substantial; opioid often required.
Treatment of underlying disease (IBD, RA, haematological) often improves PG control.
Multidisciplinary input — dermatology, gastroenterology, rheumatology, haematology, tissue viability, plastic surgery (cautiously, only after disease control).