Pyoderma Gangrenosum

Pyoderma gangrenosum (PG) is a rare, painful, ulcerative neutrophilic dermatosis characterised by rapidly expanding ulcers with undermined violaceous borders and pathergy.

• Incidence is 3 to 10 per million per year; onset 20 to 50 years; slight female predominance.
• Associated systemic disease in 50 to 70%: inflammatory bowel disease, inflammatory arthritis (rheumatoid, seronegative), haematological disease (MDS, myeloma, IgA gammopathy, AML), and hidradenitis suppurativa; also PAPA, PASH, and PAPASH syndromes.
• Pathergy: lesions develop at sites of minor trauma or surgery.
• Variants: ulcerative (classic), bullous (haematological), pustular (IBD), vegetative, peristomal, genital, and extracutaneous (lung, spleen).

• Starts as a tender papule, pustule, or nodule that rapidly breaks down into a painful ulcer with a purulent base, a violaceous overhanging border, and surrounding erythema.
• Common on lower legs, trunk, and peristomal skin; pain is disproportionate.
• Heals with thin, cribriform ("wrinkled paper") scars.
• Systemic: fever, arthralgia, malaise.

• Diagnosis of exclusion. PARACELSUS score or Delphi consensus criteria: major criterion biopsy showing neutrophilic infiltrate; minor criteria include exclusion of infection, pathergy, history of IBD or arthritis, rapid progression, peripheral erythema with undermined border, multiple ulcers with cribriform scars, and response to immunosuppression.
• Biopsy from the active edge (with culture and DIF) to exclude infection (tuberculosis, atypical mycobacteria, deep fungi), vasculitis, malignancy, and venous or arterial ulcers.
• Investigations: FBC, ESR, CRP, glucose, LFTs, SPEP and immunofixation, ANCA, antiphospholipid antibodies, hepatitis B and C, HIV, TB quantiferon, colonoscopy, and chest X-ray.
• Doppler studies to exclude venous or arterial disease.

• Avoid surgical debridement without immunosuppression (pathergy).
• Local disease (small ulcers): clobetasol 0.05% ointment to the ulcer edge or tacrolimus 0.1% ointment; intralesional triamcinolone 10 mg/mL at the border; non-adherent dressings.
• Systemic first line: prednisolone 0.5 to 1 mg/kg/day (maximum 60 to 80 mg) or ciclosporin 3 to 5 mg/kg/day (similar efficacy in a randomised trial; about 50% healed at 6 months).
• Biologics: infliximab 5 mg/kg at weeks 0, 2 and 6 then every 8 weeks (randomised evidence), adalimumab 80 mg then 40 mg every 1 to 2 weeks, ustekinumab, secukinumab, canakinumab, or JAK inhibitors. Anakinra, IVIG 2 g/kg monthly in refractory disease.
• Steroid sparing: azathioprine, mycophenolate 1 g twice daily, methotrexate, dapsone 100 to 200 mg, and colchicine.
• Adjunctive: pain control (including neuropathic agents), compression therapy for coexistent venous disease, wound care, bone protection, and treatment of underlying IBD or malignancy.
• Skin grafting only once disease is quiescent on immunosuppression.