Ulcerative colitis (UC) causes inflammation and ulceration in the innermost lining of the large intestine. The large intestine is made up of the cecum, ascending/transverse/descending/sigmoid  colon and rectum. In most cases of UC, inflammation begins in the rectum and extends upward into the colon.

UC can be classified into various types, depending on how much of the large intestine is involved. Types of UC include:

• Ulcerative proctitis. Inflammation occurs in the rectum. Ulcerative proctitis is a common and typically mild form of UC. However, it may be a precursor to more serious forms of UC. Approximately 30 percent of all patients with UC were first diagnosed with ulcerative proctitis, according to the Crohn’s & Colitis Foundation of America (CCFA).
  
  
• Proctosigmoiditis. Inflammation of the rectum and lower portion of the colon (sigmoid colon). When symptoms are active, patients with this type of UC may experience moderate pain in the lower left-hand area of the abdomen.
  
  
• Left-sided colitis (sometimes referred to as limited or distal colitis). Occurs along the left side of the large intestine, from the rectum into the splenic flexure (a bend in the colon, where the transverse and descending colons meet). Symptoms include diarrhea, bloody stool, loss of appetite, weight loss and severe pain on the left side of the abdomen.
  
  
• Pancolitis. Affects the entire colon and rectum. Symptoms include diarrhea, severe abdominal pain, cramping, weight loss and night sweats. Serious complications, such as intestinal perforation and massive bleeding, can result from pancolitis, requiring surgery.
  
  
• Fulminant colitis. A rare but life-threatening condition that affects the entire colon and rectum, causing severe pain and diarrhea. Patients with this type of UC are at risk of developing toxic megacolon, when the large intestine widens and loses muscle tone. Abdominal distention and rupture may occur, requiring immediate medical attention.