Current clinical issue of skin lesions in patients with inflammatory bowel disease.

Inflammatory bowel disease (IBD) is associated with a number of extraintestinal complications, including skin lesions. Most reports have shown that skin lesions are found in 10-15% of IBD cases, although this depends on the definition of skin lesions. The representative skin lesions in patients with IBD are erythema nodosum, pyoderma gangrenosum, Sweet's syndrome, and so on. These lesions are often associated with IBD progression, and intestinal lesions in particular require appropriate treatment. Recently, another clinical issue regarding skin lesions in patients with IBD, a so-called paradoxical reaction, during the treatment with anti-tumor necrosis factor (TNF)-α agents has emerged. These reactions are termed paradoxical reactions because the skin lesions sometimes resemble psoriasis, although the anti-TNF-α agents have been historically used to treat psoriasis. Paradoxical reactions are reportedly found in approximately 5-10% of patients using anti-TNF-α agents and are no longer rare. Now that the use of biologics is at its culmination, reports regarding paradoxical reactions are predicted to increase in number; thus, we must recognize skin lesions with IBD patients including this type of adverse events and manage them appropriately while consulting with dermatologists.