The highest incidence of ulcerative colitis occurs in temperate climates and in Caucasians, the populations of Europe, Australasia and North America being the most commonly affected. Annual incidence rates combined with the number of new cases diagnosed per 100000 population per year vary between 3.3 and 6.5. Ulcerative colitis is about two to three times more common than Crohn's disease, and there is little evidence to suggest that its incidence is increasing, although most studies show an increasing incidence of Crohn's disease. Improved awareness of Crohn's disease and its distinction from ulcerative colitis are not sufficient to account for this increase.[ss

Both ulcerative colitis and Crohn's disease are usually diagnosed in patients between 15 and 40 years of age. The actual age of peak incidence varies between series and there is a second peak in later years.

Ulcerative colitis is more common in men, whereas Crohn's disease is more common in women. Both diseases have a higher incidence among Jewish people.

The number of patients with the disease per 10&sup5; population at risk varies between 37.4 and 79.9 for ulcerative colitis.

There is an increased incidence of ulcerative colitis in the close relatives of patients with the disease. Ankylosing spondylitis can occur in the same families, with or without inflammatory bowel disease. The histocompatibility antigen HLA B27 is found in most patients with colitis and ankylosing spondylitis, but no histocompatibility antigen is clearly associated with inflammatory bowel disease alone. The familial tendency of the disease has been interpreted as being due to similar childhood environment or inherited factors, but the rarity of ulcerative colitis in spouses and its recurrence in different generations in widely separated branches of the family make this less likely.

Circulating humoral antibodies to an antigen present in colonic epithelial cells and to certain bacteria can be demonstrated in the peripheral blood of some patients with ulcerative colitis. Antibody-dependent cytotoxicity against colonic epithelial cells can also be demonstrated in tissue culture. Normal lymphocytes become cytotoxic after incubation with a serum of a patient with colitis. Immune complexes can be demonstrated both in the circulation and within the mucosa. Immune complexes in the lamina propria may cause activation of the complement pathway, with attraction of leucocytes and local tissue damage. Local sensitivity to one or more food antigens has been suggested as a factor. The presence of antibodies to milk protein does not correlate with the duration or severity of disease. However, normal permeability of the intestinal wall to these antigens may be increased when the mucosa is inflamed and the presence of circulating antibodies to food or bacterial antigens may be a secondary effect.

There are no striking differences between normal stool and the faeces of patients with ulcerative colitis. It is possible that normal bacterial flora may play a role in the aetiology of the disease, although no specific antigen has been identified. Cross-reactivity between a bacterial antigen and a mucopolysaccharide present in colonic epithelial cells may precipitate a self-perpetuating autoimmune reaction resulting from a sensitivity to the bacterial antigen. Local mucosal antibodies to anaerobic organisms can also be demonstrated. A first attack of ulcerative colitis can follow a bowel infection, supporting the idea that contact with bacterial antigens due to damage of normal mucosal defences can play a role in the development of the condition.

The rarity of ulcerative colitis in Africa and the Far East and its relative prevalence in the Western world suggests that environmental factors may be important, but no specific dietary components have been implicated.

Bloody diarrhoea in an otherwise fit patient is the most common presenting symptom. Patients with a limited proctitis may complain of either tenesmus or constipation. Severe disease may cause most constant diarrhoea with cramping abdominal pain, urgency, and episodes of incontinence. The well recognized extraintestinal manifestations of ulcerative colitis are listed in Table 2 328 in Section 18.2.2.

Examination of the patient may reveal nothing of note in the abdomen or, occasionally, some tenderness in the left iliac fossa and signs of anaemia. Rectal examination reveals blood and mucus on the glove, and the mucosa may feel velvety. Sigmoidoscopy shows a confluent proctitis with contact bleeding, ulceration, and granularity (Fig. 1) 1039. It is important to assess the upper limit of disease. Rectal biopsies should be taken from the posterior wall of the rectum below the peritoneal reflection to avoid iatrogenic perforation.

Although a double-contrast barium enema will demonstrate the full extent of macroscopic disease (Fig. 2) 1040, colonoscopy is the most useful investigation. The characteristic appearance on colonoscopy is of an erythematous mucosa, with or without ulceration which may bleed on contact (Fig. 3) 1041. A normal vascular pattern is lost and there may be blood and pus in the lumen. Even when the mucosa appears normal, biopsy specimens should be taken to define the exact limit of disease. Ulcerative colitis is worse in the rectum and extends more proximally, but treatment with local steroids may give an appearance of relative rectal sparing. Great care should be taken in conducting either a barium enema or colonoscopy in patients with severe colitis to avoid perforation. Blood samples should be taken to allow the presence of anaemia and signs of systemic inflammation to be assessed. Other tests should include measurement of ESR or viscosity, C-reactive protein albumin, and to assess nutritional status.

Good medical management is vital to prevent progression of disease and severe relapses. It is aimed at reducing inflammation, pain, and diarrhoea. A combination of aggressive medical treatment and conservative surgery ensures the best joint management of patients with severe disease.

Controlled trials have shown that corticosteroids have a therapeutic effect in ulcerative colitis. Severely ill patients can be given intravenous prednisolone, while in those with less severe disease oral prednisolone is effective, usually starting with a dose of 40 to 60 mg. Topical preparations in the form of foam or retention enemata, can be used when the inflammation is limited to the distal colon and rectum.

Sulphasalazine is a combination of sulphapyridine and 5-aminosalicylic acid. It is poorly absorbed in the small intestine and is split in the colon by a bacterial action to liberate the active 5-aminosalicylic acid. This reduces inflammation and is used to prevent relapse. Sulphapyridine is, however, responsible for side-effects such as dyspepsia, skin rashes, and azoospermia. Intolerant patients can be given an enteric-coated preparation or one of the more recently developed 5-aminosalicylate preparations, such as mesalazine or olsalazine.

Azathioprine either in combination with steroids or alone can be used to reduce steroid doses needed for maintenance and prolongation of remission. Side-effects include bone marrow depression, skin rash, and febrile reactions. Azathioprine is usually reserved for the patients with the most resistant chronic disease.

There is no evidence that antibacterial agents have any effect in ulcerative colitis, but intravenous antibiotics may be administered to some patients with severe ulcerative colitis prior to surgery.

Treatment with loperamide, codeine phosphate, or diphenoxylate decreases stool frequency and water and electrolyte losses, but it is not recommended. It may mask signs of severe disease and may precipitate a toxic dilatation. If the proximal colon is normal, hard constipated stool may accumulate proximal to the diseased left colon and treatment with a stool softening or bulking agent may be necessary.