Skin signs in inflammatory bowel disease

Overview

•IBD (Crohn's disease and UC) causes extra-intestinal skin manifestations in up to 40% of patients

•Key skin signs: erythema nodosum, pyoderma gangrenosum (PG), aphthous ulcers, psoriasis, perianal skin changes (CD)

•CD affects the GI tract from mouth to anus; most commonly affects the ileum - explaining weight loss from malabsorption

Presentation

Key IBD skin signs
FeatureErythema nodosumPyoderma gangrenosum
MorphologyTender, raised red/violet subcutaneous nodules, 1-5 cm; do not ulcerateBegins as painful papule/pustule → deep necrotic ulcer with violaceous, undermined overhanging edge
SiteAnterior tibial/extensor surfacesShin most common; also peristomal skin
IBD associationMore common in CD; tracks bowel activityMore common in UC; may be independent of bowel activity
ResolutionResolves with IBD control (bruise-like colour change over 3-6 weeks)Requires specific treatment; do NOT biopsy or debride

Feature	Erythema nodosum	Pyoderma gangrenosum
Morphology	Tender, raised red/violet subcutaneous nodules, 1-5 cm; do not ulcerate	Begins as painful papule/pustule → deep necrotic ulcer with violaceous, undermined overhanging edge
Site	Anterior tibial/extensor surfaces	Shin most common; also peristomal skin
IBD association	More common in CD; tracks bowel activity	More common in UC; may be independent of bowel activity
Resolution	Resolves with IBD control (bruise-like colour change over 3-6 weeks)	Requires specific treatment; do NOT biopsy or debride

•Aphthous ulcers - painful, shallow oral ulcers; common in CD (mouth-to-anus involvement); track disease activity

•Perianal skin changes (CD) - skin tags, fissures, fistulae; up to 50% of CD patients; due to transmural inflammation

•Psoriasis - more prevalent in IBD; runs an independent course from gut disease activity

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Pyoderma gangrenosum exhibits pathergy - minor trauma (biopsy, surgery, poorly fitting stoma appliance) triggers new lesions or extends existing ones. Biopsy and surgical debridement are contraindicated. Diagnosis is clinical.

Differential diagnosis

•PG vs SCC at stoma site - PG: acutely painful, rapidly progressive, purple overhanging edge; SCC: painless, slow-growing, indurated; history of IBD and rapid progression favour PG

•Other PG differentials: vasculitic/venous/arterial ulcers, bullous pemphigoid, pemphigus vulgaris, poorly fitting stoma appliance

•Other causes of erythema nodosum: sarcoidosis, streptococcal infection, TB, drugs (sulphonamides, OCP), pregnancy

Management

•Erythema nodosum - treat underlying IBD; EN resolves with bowel disease control; NSAIDs for symptomatic relief (use cautiously - can exacerbate IBD)

•Aphthous ulcers - topical hydrocortisone (Corlan pellets) or benzydamine mouthwash for symptom relief; IBD control is definitive

•Pyoderma gangrenosum - first-line: high-dose systemic prednisolone; do not debride or biopsy

🥈 Second-line

•ciclosporin - if steroids fail or contraindicated

•infliximab (anti-TNF) - especially useful when PG coexists with active IBD requiring biological therapy

•Wound care: moist, non-adherent dressings; avoid adherent dressings (risk of pathergy on removal)

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Infliximab can paradoxically cause or worsen psoriasiform skin reactions ('paradoxical psoriasis') in a small proportion of IBD patients - do not confuse with a new IBD-related skin manifestation.

Melanosis coli

•Abnormal pigmentation of the large bowel due to pigment-laden macrophages (seen on PAS staining)

•Most common cause: laxative abuse; not associated with C. difficile or antibiotics

•Generally benign, though some studies associate it with polyps and adenomas