炎症性腸疾患I:はじめに

Inflammatory bowel disease refers to recurrent inflammation of the gastrointestinal tract resulting from an abnormal immune response against gut microflora. This chronic disorder leads to tissue damage and includes two main forms: Crohn's disease and ulcerative colitis. Both conditions cause inflammation but differ in location and depth of involvement within the GI tract.

Crohn's disease can affect any part of the GI tract from the mouth to the anus and involves all bowel wall layers with skip lesions where diseased areas alternate with normal tissue. Ulcerative colitis is limited to the colon and rectum, affecting only the mucosa and submucosa, and spreads continuously from the rectum without skip lesions.

Crohn's disease is classified by affected areas: ileocolitis involves the terminal ileum and colon; ileitis is confined to the ileum; Crohn's colitis affects the colon; gastroduodenal disease involves the stomach and duodenum; jejunoileitis affects the jejunum and ileum; and perianal disease involves tissues around the anus.

Ulcerative colitis presents in distinct patterns: proctitis affects only the rectum; proctosigmoiditis involves the rectum and sigmoid colon; left-sided colitis extends to the splenic flexure; and pancolitis involves the entire colon. Each pattern reflects progressive inflammation spreading continuously from the rectum.

Ileocolitis, the most common form of Crohn's disease affecting the terminal ileum and colon, causes diarrhea, cramping, weight loss, and right lower abdominal pain. These symptoms result from inflammation in both the small and large intestines, making it the most frequently diagnosed Crohn's subtype.

Pancolitis involves the entire colon and produces more severe symptoms than localized patterns, including profuse diarrhea, abdominal pain, and significant weight loss. Pancolitis also carries an increased risk of colon cancer compared to other ulcerative colitis extent patterns, making it the most serious presentation.

Perianal disease, a form of Crohn's disease affecting tissues around the anus, can develop abscesses, fistulas, fissures, and skin tags. These complications result from transmural inflammation extending through all bowel wall layers to surrounding tissues, causing significant morbidity and requiring specialized management.