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A 32-year-old man was diagnosed with Crohn disease 10 years prior to his visit for these nonhealing leg ulcers (Figure 174-1). The patient experienced minor trauma to his lower leg 1 year ago and these ulcers developed (pathergy). Multiple treatments have been tried with partial success, but the ulcers persist.

Figure 174-1

Classic pyoderma gangrenosum on the leg of a 32-year-old man with Crohn disease. This ulcer started with minor trauma (pathergy) and has been there for 1 year. (Courtesy of Richard P. Usatine, MD.)

Pyoderma gangrenosum (PG) is an uncommon ulcerative disease of the skin of unknown origin. It is a type of neutrophilic dermatosis.

  • PG occurs in approximately 1 person per 100,000 people each year.1
  • No racial predilection is apparent.
  • A slight female predominance may exist.
  • Predominately occurs in fourth and fifth decade, but all ages may be affected.

  • Etiology is poorly understood.
  • Pathergy (initiation at the site of trauma or injury) is a common process and it is estimated that 30% of patients with PG experienced pathergy.1
  • Up to 50% of cases are idiopathic.2
  • At least 50% of cases are associated with systemic diseases such as inflammatory bowel disease, hematologic malignancy, and arthritis.2
  • It occurs in up to 5% of patients with ulcerative colitis and 2% of those with Crohn disease (Figures 174-2 and 174-3).3,4
  • Biopsies usually show a polymorphonuclear cell infiltrate with features of ulceration, infarction, and abscess formation.

Figure 174-2

Friable inflamed mucosa of the colon in Crohn disease. (Courtesy of Shashi Mittal, MD.)

Figure 174-3

Classic pyoderma gangrenosum on the leg of a 35-year-old woman with Crohn disease. This ulcer started with minor trauma (pathergy) and has been there for 2 years. (Courtesy of Richard P. Usatine, MD.)

  • Ulcerative colitis.2,5
  • Crohn disease.
  • Polyarthritis (seronegative or seropositive).
  • Hematologic diseases/disorders such as leukemia (predominantly myelocytic).
  • Monoclonal gammopathies (primarily immunoglobulin A).
  • Psoriatic arthritis and rheumatoid arthritis (Figure 174-4).
  • Hepatic diseases (hepatitis and primary biliary cirrhosis).
  • Immunologic diseases (lupus erythematosus and Sjögren syndrome).

Figure 174-4

Pyoderma gangrenosum on the leg of a 56-year-old woman with rheumatoid arthritis. (Courtesy of Richard P. Usatine, MD.)

Clinical Features

  • Typically PG presents with deep painful ulcer with a well-defined border, which is usually violet or blue. The color has also been described as the color of gun metal. The ulcer edge is often undermined and the surrounding skin is erythematous and indurated. It usually starts as a pustule with an inflammatory base, ...

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