Pyoderma gangrenosum

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.

• 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

• 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

• location
• typically on the lower limb
• soften at the site of a minor injury as in this patient's case and 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

• often made by the characteristic appearance, associations with other diseases, the presence of pathergy, histology results and when other diseases have been ruled out
• histology is not specific and can vary depending on the time and site of the specimen but may be helpful in ruling out other causes of an ulcer.

• the potential for rapid progression is high in most patients and most doctors advocate oral steroids as first-line treatment
• other immunosuppressive therapy, for example, ciclosporin and infliximab, have a role in difficult cases
• any surgery should be postponed until the disease process is controlled on immunosuppression to risk worsening of the disease (pathergy)