The signs and symptoms of colitis are quite variable and dependent on the cause of the given colitis and factors that modify its course and severity.

Symptoms of colitis may include: mild to severe abdominal pain and tenderness (depending on the stage of the disease), recurring bloody diarrhea with/without pus in the stools, fecal incontinence, flatulence, fatigue, loss of appetite and unexplained weight loss.

More severe symptoms may include: shortness of breath, a fast or irregular heartbeat and fever.

Other less or rare non-specific symptoms that may accompany colitis include: arthritis, mouth ulcers, painful, red and swollen skin and irritated, red eyes.

Signs seen on colonoscopy include: colonic mucosal erythema (redness of the inner surface of the colon), ulcers, and bleeding.

People who develop microscopic colitis are characteristically, though not exclusively, middle-aged females. The average age of diagnosis is 65 but 25% of cases are diagnosed below the age of 45. Patients have a history of non-bloody watery diarrhoea, which may be profuse. Patients may also experience abdominal pain, fecal incontinence, and weight loss. Microscopic colitis is the diagnosis in around 10% of cases investigated for chronic non-bloody diarrhea.

Colonoscopic appearances are normal or near normal. As the changes are often patchy, an examination limited to the rectum may miss cases of microscopic colitis, and so a full colonoscopy is necessary. Multiple colonic biopsies are taken in order to make the diagnosis. Histological features of colonic biopsies indicating microscopic colitis are: greater than 20 intraepithelial lymphocytes per 100 epithelial cells and, additionally, 10-20 μm of a thickened subepithelial collagen band in collagenous colitis. Inflammation of the lamina propria, with mainly mononuclear cells, may be observed in collagenous colitis.

Differential diagnoses, which should be ruled out, include celiac disease, Crohn's disease, ulcerative colitis and infectious colitis.

Microscopic colitis refers to two related medical conditions which cause diarrhea: collagenous colitis and lymphocytic colitis. Both conditions are characterized by the presence of chronic non-bloody watery diarrhea, normal appearances on colonoscopy and characteristic histopathology findings of inflammatory cells.

There are many types of colitis. They are usually classified by the cause.

Types of colitis include:

Microscopic colitis causes chronic watery diarrhea with greater than 10 bowel movements per day. Some patients report nocturnal diarrhea, abdominal pain, urgency, fecal incontinence, fatigue, dehydration and weight loss. Patients report a significantly diminished quality of life.

Enterocolitis or coloenteritis is an inflammation of the digestive tract, involving enteritis of the small intestine and colitis of the colon. It may be caused by various infections, with bacteria, viruses, fungi, parasites, or other causes. Common clinical manifestations of enterocolitis are frequent diarrheal defecations, with or without nausea, vomiting, abdominal pain, fever, chills, alteration of general condition. General manifestations are given by the dissemination of the infectious agent or its toxins throughout the body, or – most frequently – by significant losses of water and minerals, the consequence of diarrhea and vomiting.

Among the causal agents of acute enterocolitis are:

- bacteria: "Salmonella", "Shigella", "Escherichia coli", "Campylobacter" etc.;

- viruses: enteroviruses, rotaviruses, Norwalk virus, adenoviruses;

- fungi: candidiasis, especially in immunosuppressed patients or who have previously received prolonged antibiotic treatment;

- parasites: "Giardia lamblia" (with high frequency of infestation in the population, but not always with clinical manifestations), "Balantidium coli", "Blastocystis homnis", "Cryptosporidium" (diarrhea in people with immunosuppression), "Entamoeba histolytica" (produces the amebian dysentery, common in tropical areas).

In addition to the extent of involvement, people may also be characterized by the severity of their disease.

- "Mild disease" correlates with fewer than four stools daily, with or without blood, no systemic signs of toxicity, and a normal erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP). Mild abdominal pain or cramping may occur. Patients may believe they are constipated when in fact they are experiencing tenesmus, which is a constant feeling of the need to empty the bowel accompanied by involuntary straining efforts, pain, and cramping with little or no fecal output. Rectal pain is uncommon.

- "Moderate disease" correlates with more than four stools daily, but with minimal signs of toxicity. Patients may display anemia (not requiring transfusions), moderate abdominal pain, and low grade fever, .

- "Severe disease", correlates with more than six bloody stools a day or observable massive and significant bloody bowel movement, and evidence of toxicity as demonstrated by fever, tachycardia, anemia or an elevated ESR or CRP.

- "Fulminant disease" correlates with more than ten bowel movements daily, continuous bleeding, toxicity, abdominal tenderness and distension, blood transfusion requirement and colonic dilation (expansion). Patients in this category may have inflammation extending beyond just the mucosal layer, causing impaired colonic motility and leading to toxic megacolon. If the serous membrane is involved, a colonic perforation may ensue. Unless treated, the fulminant disease will soon lead to death.

Specific types of enterocolitis include:

- necrotizing enterocolitis (most common in premature infants)

- pseudomembranous enterocolitis (also called "Pseudomembranous colitis")

Ulcerative colitis is normally continuous from the rectum up the colon. The disease is classified by the extent of involvement, depending on how far the disease extends:

- "Distal colitis", potentially treatable with enemas:

- "Proctitis": Involvement limited to the rectum.

- "Proctosigmoiditis": Involvement of the rectosigmoid colon, the portion of the colon adjacent to the rectum.

- "Left-sided colitis": Involvement of the descending colon, which runs along the patient's left side, up to the splenic flexure and the beginning of the transverse colon.

- "Extensive colitis", inflammation extending beyond the reach of enemas:

- "Pancolitis": Involvement of the entire colon, extending from the rectum to the cecum, beyond which the small intestine begins.

In spite of Crohn's and UC being very different diseases, both may present with any of the following symptoms: abdominal pain, vomiting, diarrhea, rectal bleeding, severe internal cramps/muscle spasms in the region of the pelvis and weight loss. Anemia is the most prevalent extraintestinal complication of inflammatory bowel disease. Associated complaints or diseases include arthritis, pyoderma gangrenosum, primary sclerosing cholangitis, and non-thyroidal illness syndrome (NTIS). Associations with deep vein thrombosis (DVT) and bronchiolitis obliterans organizing pneumonia (BOOP) have also been reported. Diagnosis is generally by assessment of inflammatory markers in stool followed by colonoscopy with biopsy of pathological lesions.

On colonoscopy, the mucosa of the colon typically looks normal, but biopsies of affected tissue usually show deposition of collagen in the lamina propria, which is the area of connective tissue between colonic glands. Radiological tests, such as a barium enema are also typically normal.

Once a diagnosis of pouchitis is made, the condition is further classified. The activity of pouchitis is stratified as:

- remission (no active pouchitis).

- mild to moderately active (increased stool frequency, urgency, infrequent incontinence).

- severely active (hospitalised for dehydration, frequent incontinence).

The duration of pouchitis is defined as acute (less than or equal to four weeks) or chronic (four weeks or more) and the pattern classified as infrequent (1-2 acute episodes), relapsing (three or fewer episodes) or continuous. Finally, the response to medical treatment as labelled as treatment responsive or treatment refractory, with the medication for either case being specified.

Inflammatory bowel disease (IBD) is a group of inflammatory conditions of the colon and small intestine. Crohn's disease and ulcerative colitis are the principal types of inflammatory bowel disease. It is important to note that not only does Crohn's disease affect the small intestine and large intestine, it can also affect the mouth, esophagus, stomach and the anus whereas ulcerative colitis primarily affects the colon and the rectum.

In histology, cryptitis refers to inflammation of an intestinal crypt.

Cryptitis is a non-specific histopathologic finding that is seen in several conditions, e.g. inflammatory bowel disease, diverticular disease, radiation colitis, infectious colitis.

Pouchitis is inflammation of the ileal pouch (an artificial rectum surgically created out of ileal gut tissue in patients who have undergone a colectomy), which is created in the management of patients with ulcerative colitis, indeterminate colitis, FAP, or, rarely, other colitides.

A variety of pathophysiological mechanisms have been proposed for pouchitis, but the precise pathogenesis (biological cause) remains unknown. A pilot study on the effect of reducing dietary FODMAP intake on bowel function in patients without a colon ran by Croagh C, Shepherd SJ, Berryman M, Muir JG, Gibson PR indicates there might be a relation between Pouchitis and FODMAP content of diets.

The incidence of a first episode of pouchitis at 1, 5 and 10 years post-operatively is 15%, 33% and 45% respectively.

Patients with pouchitis typically present with bloody diarrhea, urgency in passing stools, or discomfort while passing stools. The loss of blood and/or dehydration resulting from the frequent stools will frequently result in nausea. Extreme cramping and pain can occur with pouchitis.

Endoscopy in patients with pouchitis usually reveals erythematous pouch mucosa, loss of pseudocolonic vasculature or other architecture, and friability of the mucosa. Biopsies show evidence of inflammatory cells or red blood cells in the lamina propria.

Chemical colitis is a type of colitis, an inflammation of the large intestine or colon, caused by the introduction of harsh chemicals to the colon by an enema or other procedure. Chemical colitis can resemble ulcerative colitis, infectious colitis and pseudomembranous colitis endoscopically.

Prior to 1950, hydrogen peroxide enemas were commonly used for certain conditions. This practice will often result in chemical colitis.

Soap enemas may also cause chemical colitis.

Harsh chemicals, such as compounds used to clean colonoscopes, are sometimes accidentally introduced into the colon during colonoscopy or other procedures. This can also lead to chemical colitis.

Chemical colitis may trigger a flare of ulcerative colitis or Crohn's colitis. Symptoms of colitis are assessed using the Simple Clinical Colitis Activity Index.

Signs and symptoms of enteritis are highly variable and vary based on the specific cause and other factors such as individual variance and stage of disease.

Symptoms may include abdominal pain, cramping, diarrhoea, dehydration, fever, nausea, vomiting and weight loss.

Lymphocytic colitis is a subtype of microscopic colitis, a condition characterized by chronic non-bloody watery diarrhea. The colonoscopy is normal but histology of the mucosal biopsy reveals an accumulation of lymphocytes in the colonic epithelium and connective tissue (lamina propria). Collagenous colitis shares this feature but additionally shows a distinctive thickening of the subepithelial collagen table. The peak incidence of lymphocytic colitis is in persons over age 50; the disease affects women and men equally. Lymphocytic colitis was first described in 1989.

The diagnosis of CMV colitis is based on serology, CMV antigen testing and colonscopy with biopsy.

Clinical suspicion should be aroused in the setting of immunocompromised patient but it is much rarer in immunocompetent patient.

Although it is known that CMV colitis is almost always caused by reactivation of latent CMV infection in immunocompromised patients, new infection of CMV or reinfection of different strain of CMV can cause colitis in immunocompetent hosts.

Because asymptomatic CMV viremia and viruria is common and about 1/3 of symptomatic CMV infection is caused by reinfection of different strain of CMV, the diagnosis of CMV colitis needs more direct causality. It is practically achieved by colonoscopy or sigmoidoscopy tissue sampling and pathological evidence of CMV infection under microscope. Positive CMV IgG doesn't necessarily mean that it is reactivation of latent infection because of the possibility of reinfection of different strain.

Pancolitis or universal colitis is a very severe form of ulcerative colitis. This form of ulcerative colitis is spread throughout the entire large intestine including the right colon, the left colon, the transverse colon, descending colon, and the rectum. A diagnosis can be made using a number of techniques but the most accurate method is direct visualization via a colonoscopy. Symptoms are similar to those of ulcerative colitis but more severe and affect the entire large intestine. Patients with ulcerative colitis generally exhibit symptoms including rectal bleeding as a result of ulcers, pain in the abdominal region, inflammation in varying degrees, and diarrhea (often containing blood). Pancolitis patients exhibit these symptoms and may also experience fatigue, fever, and night sweats. Due to the loss of function in the large intestine patients may lose large amounts of weight from being unable to procure nutrients from food. In other cases the blood loss from ulcers can result in anemia which can be treated with iron supplements. Additionally, due to the chronic nature of most cases of pancolitis, patients have a higher chance of developing colon cancer.

Pancolitis is a kind of inflammatory bowel disease (IBD) that affects the entire internal lining of the colon. The precise causes of this inflammatory disorder are unclear, although physicians currently believe that autoimmune diseases and genetic predispositions might play a role in its progress. Genes that are known to put individuals at risk for Crohn’s disease have been shown to also increase risk of other IBD including pancolitis. Furthermore, an individual may also develop pancolitis if ulcerative colitis of only a small portion of the colon is left untreated or worsens. Current treatment of pancolitis is focused on forcing the disease into remission, a state where the majority of the symptoms subside. Ultimately, the goal is to reach an improved quality of life, reduction in need for medicine, and minimization of the risk of cancer. Medication utilized in treatment includes anti-inflammatory agents and corticosteroids to alleviate inflammation and immunomodulators which act to suppress the immune system. Immunomodulators are used in severe cases of ulcerative colitis and often utilized to treat patients with pancolitis who have shown little improvement with anti-inflammatories and corticosteroids. However, in this case it can further expose the patient to other diseases due to the compromised immune system. A final option of treatment is available in the form of surgery. Generally, this option is reserved for only the cases in which cancer development is highly suspected or major hemorrhaging from ulcers occurs. In this case the entire colon and rectum are removed which both cures the pancolitis and prevents any chance of colon cancer. Patients who undergo surgery either must have their stool collect in a reservoir made in place of the rectum or have the end of the small intestine attached to the anus. In the latter case the diseased portion of the anus must be removed, but the muscles are left intact, allowing bowel movement to still take place.

Colitis-X is a term used for colitis cases in which no definitive diagnosis can be made and the horse dies. Clinical signs include sudden, watery diarrhea that is usually accompanied by symptoms of hypovolemic shock and usually leads to death in 3 to 48 hours, usually in less than 24 hours. Other clinical signs include tachycardia, tachypnea, and a weak pulse. Marked depression is present. An explosive diarrhea develops, resulting in extreme dehydration. Hypovolemic and endotoxic shock are manifest by increased capillary refill time, congested or cyanotic (purplish) mucous membranes, and cold extremities. While there may initially be a fever, temperature usually returns to normal.

Clinical signs are similar to those of other diarrheal diseases, including toxemia caused by "Clostridium", Potomac horse fever, experimental endotoxic shock, and anaphylaxis.

Enteritis is inflammation of the small intestine. It is most commonly caused by food or drink contaminated with pathogenic microbes. but may have other causes such as NSAIDs, cocaine, radiation therapy as well as autoimmune conditions like Crohn's disease and coeliac disease. Symptoms include abdominal pain, cramping, diarrhoea, dehydration, and fever. Related diseases include inflammation of the stomach (gastritis) and large intestine (colitis).

Duodenitis, jejunitis and ileitis are subtypes of enteritis which are only localised to a specific part of the small intestine. Inflammation of both the stomach and small intestine is referred to as gastroenteritis. Inflammation of related organs of the gastrointestinal system are:

- gastritis

- gastroenteritis

- colitis

- enterocolitis

Cytomegalovirus colitis, also known as CMV colitis, is an inflammation of the colon

Causes

The infection is spread by saliva, urine, respiratory droplets, sexual contact, and blood transfusions. Most people are exposed to the virus in their lifetime, but it usually produces mild or no symptoms in healthy people.

However, serious CMV infections can occur in people with weakened immune systems. This includes patients receiving chemotherapy for cancer and patients on immune-suppressing medicines following an organ transplant.

In rare instances, more severe CMV infection involving the GI tract has been reported in people with a healthy immune system.

Anoscopy can be used to diagnose the majority of cases of proctocolitis.

Fibrosing colonopathy is a disease that arises in patients with cystic fibrosis treated with enteric coated pancreatic enzyme supplements. The disease is associated with high dose of these supplements. The clinical presentation of fibrosing colonopathy is non-specific. Abdominal pain, distension, vomiting, and constipation are frequent

features and have led initially to confusion with distal intestinal obstruction syndrome. In some instances, the clinical and radiological features were suggestive of Crohn's disease or inflammatory colitis.