Skin nontumor

Dermal non-granulomatous granulocyte-rich reaction patterns

Pyoderma gangrenosum

Editorial Board Member: Kiran Motaparthi, M.D.
Bicong (Crane) Wu, M.D.
Michi Shinohara, M.D.

Last author update: 15 November 2021
Last staff update: 23 January 2023

Copyright: 2002-2023,, Inc.

PubMed Search: Pyoderma gangrenosum pathology [TIAB]

Bicong (Crane) Wu, M.D.
Michi Shinohara, M.D.
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Cite this page: Wu B, Shinohara M. Pyoderma gangrenosum. website. Accessed October 3rd, 2023.
Definition / general
  • Noninfectious neutrophilic dermatosis with painful nodules / pustules that progress to necrotic ulcers with a characteristic violaceous edge
  • Pyoderma gangrenosum is a diagnosis of exclusion based on clinical and histological findings
Essential features
  • Painful ulcers
  • Up to 50% associated with systemic disease, particularly inflammatory bowel disease
  • Diagnosis of exclusion
  • Early lesions show neutrophilic folliculitis / perfolliculitis with dermal abscess
  • Later lesions are ulcerated with mixed dermal inflammation and neutrophilic abscess that undermines the ulcer edge
ICD coding
  • ICD-10: L88 - pyoderma gangrenosum
  • Any site; most common lower legs, peristomal
  • Unknown etiology; 25 - 50% idiopathic
  • Up to 50% associated with systemic disease:
    • Inflammatory bowel disease (e.g. ulcerative colitis)
    • Arthritis
    • Hematological malignancy or monoclonal gammopathies
  • Other associated conditions: rheumatoid arthritis, seronegative arthritis, pregnancy, viral hepatitis, HIV, granulomatosis with polyangiitis
  • Reference: Clin Med (Lond) 2019;19:224
Clinical features
  • 4 major subtypes:
    • Ulcerative / classic (most common): erythematous lesion that rapidly progresses to ulcer with undermined edge, violaceous border and purulent base
      • Painful, with or without fever
      • Possible pathergy (precipitated by minor trauma)
    • Bullous: often associated with a hematological malignancy (Arch Dermatol 1972;106:901)
    • Pustular: often associated with inflammatory bowel disease (Clin Exp Dermatol 2003;28:600)
    • Vegetative / superficial granulomatous: mildly painful, verrucous quality, often without systemic condition (J Am Acad Dermatol 1988;18:511)
  • Nonspecific clinical and histologic findings; a diagnosis of exclusion
  • Proposed diagnostic criteria by Delphi Consensus of International Experts (JAMA Dermatol 2018;154:461):
    • Need major criteria + ≥ 4 minor criteria
    • Major criteria: neutrophilic infiltrate on biopsy of ulcer edge
    • Minor criteria:
      • Exclude infection
      • Pathergy
      • History of inflammatory bowel disease or inflammatory arthritis
      • History of papule, pustule, vesicle within 4 days of ulceration
      • Peripheral erythema, undermining border and tenderness
      • Multiple ulceration, at least 1 on anterior lower leg
      • Healed ulcer site with wrinkled paper scar
      • Decreased ulcer size upon initiating immunosuppressant
Prognostic factors
  • > 50% achieve complete wound healing in 1 year (Australas J Dermatol 2011;52:218)
  • Unfavorable prognostic factors: male, old age onset, bullous pyoderma gangrenosum associated with hematologic malignancy
  • Favorable prognostic factors: no underlying disease
Case reports
  • General measures: control underlying disease, manage pain, wound care, avoid trauma
  • For limited disease: topical therapy with corticosteroid and calcineurin inhibitors
  • For extensive or advanced disease: first line therapy with systemic glucocorticoids or cyclosporine; second line / adjunctive therapy with tumor necrosis factor alpha (TNF alpha) inhibitors and anti-interleukin therapy
  • Reference: Am J Clin Dermatol 2017;18:355
Clinical images

Contributed by Michi Shinohara, M.D.
Leg ulcer

Leg ulcer

Microscopic (histologic) description
  • Variable, dependent on the lesion age and site
  • Early lesion:
    • Neutrophilic folliculitis and perifolliculitis
    • Intradermal neutrophilic abscess formation
  • Later lesions:
    • Epidermal ulceration
    • Superficial dermal necrosis
    • Mixed inflammation with undermining at ulcer edge (characteristic) and abscess
    • Occasional giant cells (associated with inflammatory bowel disease)
    • Advancing edge often has subepidermal edema
    • Leukocytoclastic vasculitis and lymphocytic vasculitis may be present (J Cutan Pathol 2003;30:97)
    • Acanthosis in perilesional zone
  • Variants:
    • Ulcerative / classic variant: central neutrophilic abscess and peripheral angiocentric lymphocytic infiltrates
    • Bullous variant: subepidermal bullae and dermal neutrophilic infiltrates
    • Pustular variant: subcorneal pustules, subepidermal edema, dense dermal neutrophilic infiltrates
    • Vegetative / superficial granulomatous variant: reactive epidermal proliferation, dermal abscess, sinus tracts and palisading granulomas
Microscopic (histologic) images

Contributed by Michi Shinohara, M.D.
Early lesion

Early lesion

Late lesion Late lesion

Late lesion


Pyoderma gangrenosum versus nonspecific chronic ulcer changes

Sample pathology report
  • Skin, leg, punch biopsy:
    • Ulcer with mixed dermal inflammation (see comment)
    • Comment: The findings are nonspecific but could be compatible with pyoderma gangrenosum. Pyoderma gangrenosum is a diagnosis of exclusion and other causes of ulceration, including infection, must be ruled out.
Differential diagnosis
  • Sweet syndrome:
    • Not typically associated with ulcer, prominent karyorrhexis and deeper / more extensive inflammation
  • Infection or necrotizing fasciitis:
    • Involves deeper subcutaneous tissue; presence of microorganisms
  • Arthropod bite reaction:
    • Numerous eosinophils
  • Venous stasis ulceration:
    • Can show identical findings, usually without prominent neutrophils
    Other causes of ulcer, including factitial:
    • Can show identical findings
Board review style question #1

Which of the following systemic diseases is most often associated with pyoderma gangrenosum?

  1. Diabetes mellitus
  2. Peripheral vascular disease
  3. Systemic lupus erythematosus
  4. Ulcerative colitis
Board review style answer #1
D. Ulcerative colitis

Comment Here

Reference: Pyoderma gangrenosum
Board review style question #2
Which of the following is a feature of early pyoderma gangrenosum biopsies?

  1. Eosinophilic pustulosis
  2. Epidermal ulceration
  3. Neutrophilic folliculitis
  4. Subepidermal bullae
Board review style answer #2
C. Neutrophilic folliculitis

Comment Here

Reference: Pyoderma gangrenosum
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