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Neutrophilic dermatoses — pyoderma gangrenosum and Sweet syndrome
Neutrophilic dermatoses are non-infectious inflammatory diseases in which neutrophils infiltrate the skin; pyoderma gangrenosum (PG) is a painful ulcer with violaceous undermined edges that worsens after trauma, and Sweet syndrome is oedematous red plaques with fever and neutrophilia — both respond to steroids, not antibiotics.
Why it matters in the exam
The exam shows a patient with ulcerative colitis who develops a very painful ulcer on the shin with violaceous "undermined" edges that worsened after surgical debridement (pathergy). The question tests that the diagnosis is one of exclusion (exclude infection, vasculitis, malignancy and arterial disease), that aggressive debridement must be avoided, and that treatment is steroids, ciclosporin or TNF inhibitors. Sweet syndrome is shown as a woman with fever and painful red plaques "like a water mosaic" on the face and hands after a respiratory infection, or a patient with acute myeloid leukaemia, or after G-CSF. Remember the link of both diseases to inflammatory bowel disease, rheumatoid arthritis and haematological malignancies, and that PG at a stoma is an important cause of peristomal pain. In many stems the clue is antibiotics that did not help and a wound that worsened after surgical treatment. Biopsy shows a dense neutrophilic infiltrate without organisms.
Key points
- Neutrophilic dermatoses are non-infectious inflammatory diseases with neutrophil infiltration of the skin.
- Pyoderma gangrenosum is a painful ulcer with violaceous undermined edges that worsens after trauma and is linked to bowel disease, arthritis and blood cancers.
- PG is a diagnosis of exclusion, and treatment is steroids, ciclosporin or TNF inhibitors, without aggressive debridement.
- Sweet syndrome presents with oedematous painful red plaques, fever and neutrophilia, and responds quickly to prednisone.
- Sweet syndrome can be linked to infection, pregnancy, acute myeloid leukaemia and drugs such as G-CSF.
Summary table
| Disease | Clinical appearance | Associations | Treatment |
|---|---|---|---|
| Ulcerative pyoderma gangrenosum | Very painful ulcer, violaceous undermined edges, clean base, usually on the shins | IBD, rheumatoid arthritis, haematological malignancies, MGUS | Systemic steroids, ciclosporin, TNF inhibitors; gentle local wound care |
| Peristomal PG | Painful ulcer around the stoma opening | Crohn disease and colitis | Topical or intralesional steroids; treat the bowel disease |
| Classic Sweet syndrome | Oedematous, painful red plaques on the face and upper limbs, fever | Preceding infection, IBD, pregnancy | Moderate-dose prednisone — rapid response |
| Malignancy-associated Sweet | As classic, sometimes bullous | Acute myeloid leukaemia, MDS | Haematological work-up and prednisone |
| Drug-induced Sweet | After starting a drug | G-CSF, azathioprine, all-trans retinoic acid | Stop the drug and give steroids |
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Sources
- Delphi consensus diagnostic criteria for ulcerative pyoderma gangrenosum, 2018 — Diagnostic criteria
- ECCO guidelines on extraintestinal manifestations of inflammatory bowel disease, 2024 — Pyoderma gangrenosum and Sweet syndrome
- British Association of Dermatologists guideline on neutrophilic dermatoses, 2022 — Treatment
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.