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Other dermatoses

Pyoderma gangrenosum

Reviewer: Mowafak Hamodat MB.CH.B, MSc., FRCPC, Eastern Health, St. Johns (Canada) (see Reviewers page)
Revised: 2 August 2011, last major update August 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.


● 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 description

● Usually a deep-seated lesion
● Initially a necrotic pustule or furuncle, evolving to a large necrotic ulcer with violaceous border and surrounding erythema

Clinical images

Various images

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

eMedicine; DermNetNZ

End of Skin-nontumor > Other dermatoses > Pyoderma gangrenosum

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