Cutaneous manifestations in patients with inflammatory bowel diseases: pathophysiology, clinical features, and therapy.

The skin is one of the most common extraintestinal organ system affected in patients with inflammatory bowel disease (IBD), including both Crohn's disease and ulcerative colitis. The skin manifestations associated with IBD are polymorphic and can be classified into 4 categories according to their pathophysiology: (1) specific, (2) reactive, (3) associated, and (4) induced by IBD treatment. Cutaneous manifestations are regarded as specific if they share with IBD the same granulomatous histopathological pattern: perianal or metastatic Crohn's disease (commonly presenting with abscesses, fistulas or hidradenitis suppurativa-like features) is the prototype of this setting. Reactive cutaneous manifestations are different from IBD in the histopathology but have close physiopathological links: pyoderma gangrenosum, a neutrophil-mediated autoinflammatory skin disease typically manifesting as painful ulcers, is the paradigm of this group. Among the cutaneous diseases associated with IBD, the most commonly seen are erythema nodosum, a form of panniculitis most commonly involving bilateral pretibial areas, and psoriasis, a T helper 1/T helper 17-mediated erythematous squamous inflammatory disease. Finally, the number of cutaneous adverse reactions because of IBD therapies is progressively increasing. The most frequent drug-induced cutaneous manifestations are psoriasis-like, eczema-like, and lichenoid eruptions, as well as cutaneous lupus erythematosus for biologics, and nonmelanoma skin cancer, mainly basal cell and squamous cell carcinomas for thiopurines.