Pyoderma gangrenosum is a rare, non-infectious, inflammatory disorder. It is an uncommon cause of very painful skin ulceration. It may affect any part of the skin, but the lower legs are the most common site.

Pathophysiology

• pyoderma gangrenosum is classified as a neutrophilic dermatosis
• neutrophilic dermatoses are skin conditions characterised by dense infiltration of neutrophils in the affected tissue and this is often seen on biopsy

Causes

• idiopathic in 50%
• inflammatory bowel disease in 10-15%
  • ulcerative colitis
  • Crohn's
• rheumatological
  • rheumatoid arthritis
  • SLE
• haematological
  • myeloproliferative disorders
  • lymphoma
  • myeloid leukaemias
  • monoclonal gammopathy (IgA)
• granulomatosis with polyangiitis
• primary biliary cirrhosis

Features

• location
  • typically on the lower limb
  • often at the site of a minor injury, this is known as pathergy
• initially features:
  • usually starts quite suddenly
  • small pustule, red bump or blood-blister
• later features:
  • the skin then breaks down resulting in an ulcer which is often painful
  • the edge of the ulcer is often described as purple, violaceous and undermined.
  • the ulcer itself may be deep and necrotic
• may be accompanied by systemic symptoms
  • fever
  • myalgia