Crohn’s disease is an inflammatory disease of the intestine of unknown origin that can occur anywhere in the gastrointestinal tract, but is more prevalent in the terminal ileum and right hemicolectum. The disease and chronic nonspecific ulcerative colitis are collectively referred to as inflammatory bowel disease (IBD). The clinical manifestations of this disease are abdominal pain, diarrhea, and intestinal obstruction, accompanied by fever, nutritional disorders, and other extraintestinal manifestations. The course of the disease is prolonged, recurrent and not easily curable. The disease is also known as limited enteritis, limited ileitis, segmental enteritis and granulomatous enteritis. Clinical manifestations 1, digestive system manifestations (1) abdominal pain. It is located in the right lower abdomen or around the umbilicus, with spasmodic pain, intermittent episodes, accompanied by intestinal tinnitus, aggravated after meals, and relieved after defecation. If the abdominal pain persists and the pressure pain is obvious, it suggests that the inflammation has spread to the peritoneum or the abdominal cavity and formed an abscess. Severe pain throughout the abdomen and abdominal muscle tension may be the result of acute perforation of the diseased intestinal segment. (2) Diarrhea. Caused by inflammatory exudation, increased peristalsis and secondary malabsorption of the diseased bowel segment. It starts with intermittent episodes and later becomes persistent charcoal stools without pus, blood or mucus. If the lesion involves the lower part of the colon or rectum, there may be mucus and blood in the stool and a feeling of urgency. (3) Abdominal mass. They are caused by intestinal adhesions, thickening of the intestinal wall and mesentery, enlarged mesenteric lymph nodes, internal fistula or local abscess formation. (4) Fistula formation. It is one of the clinical features of Crohn’s disease. The fistula is formed by a transmural inflammatory lesion that penetrates the entire intestinal wall to the extraintestinal tissues or organs. Internal fistulas may lead to other intestinal segments, mesentery, bladder, ureter, and retroperitoneum of the vagina. External fistulas lead to the abdominal wall or perianal skin. (5) Peri-anorectal lesions. A few patients have perianal and perirectal fistulae, abscess formation, anal fissures and other lesions. 2. Systemic manifestations (1) Fever. Fever is caused by intestinal inflammatory activity or secondary infection, often intermittent low or moderate fever, a few are flaccid fever, may be accompanied by toxemia. (2) Nutritional disorders. Wasting, anemia, hypoproteinemia, vitamin deficiency, calcium deficiency, and osteoporosis due to loss of appetite, chronic diarrhea, and chronic wasting disease. (3) Disorders of water, electrolytes and acid-base balance during acute attacks. (3) Extra-intestinal manifestations Some patients have iridocyclitis, uveitis, pestle finger, arthritis, nodular erythema gangrenosum pyoderma, oral mucosal ulcers, chronic hepatitis, small bile duct perichondritis, sclerosing cholangitis, etc. Occasionally, amyloidosis or thromboembolic disease is seen.