Skin inflammatory (nontumor)
Dermal non-granulomatous granulocyte-rich reaction patterns
Pyoderma gangrenosum

Author: Mowafak Hamodat, M.D., MB.CH.B, MSc., FRCPC (see Authors page)

Revised: 16 October 2018, last major update August 2011

Copyright: (c) 2002-2018,, Inc.

PubMed Search: Pyoderma gangrenosum [title]

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Cite this page: Hamodat, M. Pyoderma gangrenosum. website. Accessed February 19th, 2019.
Definition / general
  • Large necrotic ulcer with violaceous border and surrounding erythema, may be immune mediated
  • 50% of cases are associated with inflammatory bowel disease, myeloma, leukemia and hepatitis
  • Usually extremities
  • Also new ulcers in areas of trauma (pathergy)
Clinical features
  • Usually a deep-seated lesion
  • Initially a necrotic pustule or furuncle, evolving to a large necrotic ulcer with violaceous border and surrounding erythema
Microscopic (histologic) description
  • Non-specific ulceration with abscess formation; involves deep dermis and subcutis
  • Adjacent dermis shows acute and chronic inflammation
  • Early lesion may present with sub-corneal pustulation
  • Histological features include leukocytoclastic and lymphocyte mediated vasculitis; vasculitis is probably secondary to inflammation, not a primary event
  • Giant cells are common; associated with inflammatory bowel disease
  • Focal and sterile abscesses are surrounded by granulomatous inflammation, bordered by rim of lymphocytes and plasma cells
  • Hemorrhage is common; often acanthosis and pseudoepitheliomatous hyperplasia; eosinophils are variable
Differential diagnosis
  • Sweet's syndrome: more karyorrhexis compared to number of neutrophils
  • Culture to exclude bacterial, mycobacterial and fungal infection
  • Bite reaction and trauma
Additional references