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Q1: What is the skin lesion shown in fig 1 (see p 788)?
Q2: What is the gastrointestinal diagnosis?
Q3: What other skin lesions are associated with this disease?
Erythema nodosum is the commonest dermatological manifestation of Crohn's disease. Sweet's syndrome (acute pyrexial neutrophilic dermatosis) is a rare complication and may represent a form of pyoderma gangrenosum. Psoriasis is also over-represented in Crohn's patients.
Pyoderma gangrenosum is a rare condition characterised by the development of painful erythematous nodules with central blue discoloration that rapidly enlarge and develop central ulceration. These ulcers typically have thickened, purple edges which may become irregular and undermined. Extensive lesions can develop at any site but there is a predilection for areas of previous minor trauma (pathergy), the calves, thighs, buttocks, and face. There are no pathognomonic histological changes but areas of ulceration are typically associated with a neutrophil-rich infiltrate of the dermis and a lymphocytic or leucocytoclastic vasculitis. Venous thrombosis with secondary infarction and haemorrhage is common.1
Pyoderma gangrenosum occurs in isolation in 45% of cases where it tends to have a female preponderance. However, in the majority of cases there is an association with either an inflammatory, haematological, or neoplastic process (box 1). Although its pathogenesis remains unclear a defective immune response seems likely based on its associations, the reported abnormalities in the type 4 contact hypersensitivity, the presence of a vasculitis on biopsy and its response to immunosuppressants. Indeed, it has been suggested that the immune complex mediated vasculitis is of primary pathological importance.2
Pyoderma gangrenosum occurs in about 2% of cases of inflammatory bowel disease (IBD) and is more likely to complicate ulcerative colitis than Crohn's disease. It has generally been reported that pyoderma gangrenosum reflects the activity of the underlying IBD, but there is increasing evidence that this is not the case; skin lesions occur when the disease is in remission and resection of the inflamed bowel may not alter pyoderma gangrenosum activity.3 Pyoderma gangrenosum may therefore be an associated disease rather than a complication of IBD. This is supported by our observation of pyoderma gangrenosum presenting two years before the clinical development of Crohn's disease in this case.
Pyoderma gangrenosum associated with neoplastic or inflammatory conditions usually responds to treatment aimed at the underlying disease. In idiopathic pyoderma gangrenosum there are no published randomised controlled trials so treatment remains empirical. High dose systemic steroids are generally used but may be required for long periods for complete healing and are not always effective.4 Concomitant immunosuppressive therapy with azathioprine or cyclosporin may be effective in some cases and there are several positive reports on alternatives therapies including salazopyrine, clofazimine, hyperbaric oxygen, and heparin.5 In all cases underlying infections should be excluded. Local treatments are generally aimed at keeping the ulcers clean, although topical therapies including steroids, cyclosporin, and sodium cromoglycate have been suggested.
Peristomal pyoderma gangrenosum is an uncommon complication of surgically treated IBD and is particularly difficult to manage as surgical debridement and stoma revision are universally unsuccessful. In such cases meticulous wound care and prolonged medical therapy with immunosuppressants are the treatments of choice.
Pyoderma gangrenosum and Crohn's disease.