Crohn's disease consist in the chronic inflammation of the gatrointestinal tract. It commonly affects the colon or the distal ileum but it may affect virtually any part of the digestive tract. The causes of this disease are not certainly known but many authors consider it an autoimmune disorder (determined by an improper immune response). There are clues that suggest a hereditary predisposition to the disease; also smoking seems to have a contribution in triggering the attacks and affecting the course of the disease. Depending on the segment affected the disease may present as jejunoileitis, ileocolitis, colitis and perianal disease, or gastroduodenal disease.

In all these clinic forms of the disease, the first symptom of the disease is in most cases chronic diarrhea (especially if the patient complaining of this symptom has had surgery), accompanied by low-grade fever, anorexia, abdominal pain and weight loss.

In ileocolitis (the most common form of the disease) the signs and symptoms are chronic diarrhea, colicky lower right quadrant pain, a palpable mass in the same quadrant and fever. As a consequence of diarrhea, fear of eating and anorexia the patient suffers a weight loss of up to 20% of his body weight. The mass consists in swollen bowel and mesentery amd it may compress the right ureter leading to dysuria. Bowel obstruction causes symptoms that vary in intensity from postprandial pain to fibrostenotic stricture (over the years). Severe inflammation may lead to wall thinning thus leading to fistula formation to the adiacent structures (bowl, skin, mesenteric abscess).

Jejunoileitis determines loss of digestive surface, thus leading to malabsorbtion (followed by nutritional deficiencies) and steatorrhea. Diarrhea is a characteristic symptom. The nutritional deficiencies may have serious consequences such as pellagra (a severe disorder caused by niacin deficit) and  megaloblastic anemia (due to lack of vitamin B12).

The signs and symptoms of colitis ans perianal disease are diarrhea, fever, malaise, crampy abdominal pain, rectal bleeding. Due to colon strictures the patient may present symptoms of bowel obstruction. The disease may produce fistulas into the stomach and duodenum ,thus leading to feculent
vomiting, and 12% of women suffering of Crohn's disease will develop a rectovaginal fistula. Perianal disease occurs in 35% of patients with Crohn colitis and its symptoms are large hemorrhoidal tags, anorectal fistulae, anal strictures, incontinence and perirectal abscesses.

In gatroduodenal disease the symptoms are: nausea, vomiting and pain in the epigastric region.

Crohn's disease may have extra-intestinal symptoms too. The dermatological manifestations of the disease are perianal skin tags (up to 80% of the patients with Crohn's colitis), erythema nodosum (up to 17% of the patients) which consists in red nodules, measuring up to 5 cm in diameter on the calves, thighs and arms and pyoderma gangrenosum (just 7% of cases). The rheumatologic manifestations occur in 15 to 20% of cases and they are represented by ankylosing spondilitis and peripheral artritis. These manifestations worsen as the disease progresses.