Skin-nontumor / Clinical dermatology
Other dermatoses
Pyoderma gangrenosum

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

Revised: 20 July 2016, last major update August 2011

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PubMed Search: Pyoderma gangrenosum [title]

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
Micro 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