Introduction

The definition of colitis is the inflammatory process of the large intestine, which connects from the end of the small intestine to the end of the rectum in the human body. There are various forms of colitis due to different aetiologies. Ischaemia, infection, abnormal immune response etc. can be the root of colitis disease. 

The four most common colitis have the following prevalence in the world: 12.6 per 100,000 person-years for ischaemic colitis from 1976 to 2009 with age-increased risk, 10.2 per 100,000 person-years for Crohn's disease and 15.7 per 100 000 person-years for ulcerative colitis from 2000 to 2018, and 25 to 30 per 100,000 for infectious colitis caused by Campylobacter jejuni, which is the most prevalent bacterium in the infectious colitis.^1,2,4 This article will briefly introduce different colitis diseases and mainly focus on ischaemic colitis and other colitis including inflammatory bowel disease and infective colitis.  

Different types of colitis

• Ischaemic colitis: "Ischaemia" means insufficient oxygenated blood flow for cells to maintain normal metabolic activity. Similarly, ischaemic colitis can be interpreted as reduced blood flow to the colon, which can lead to reversible and sometimes irreversible damage.⁴ Reversible damage includes colon mucosal ulceration, bleeding, and inflammation, and irreversible damage includes gangrene, fulminant colitis, stricture formation, and chronic ischaemic colitis.^2,5
• Inflammatory bowel disease: Inflammatory bowel disease comprises of Crohn's disease and ulcerative colitis (UC).⁷ The disease results from an abnormal immune response to gut bacteria and organisms, inducing repetitive inflammation of the gastrointestinal tract. Furthermore, serious inflammation causes further deterioration of intestinal epithelium and exaggerates the risk of microflora exposure.⁷
• Infectious colitis: Infectious colitis is caused by bacteria, viral, and parasite infections in the colon.² Escherichia coli (E.coli) is a co-existing bacteria in the human body. Although it is the normal microflora of gut tracts in humans, specific subgroups such as enterohemorrhagic E.coli cause bloody diarrhoea and toxin production. The bacterial infection could be from the intake of contaminated vegetables or poorly cooked beef.²
• Microscopic colitis: The pathogenesis of microscopic colitis is still not well-defined. It encompasses collagenous colitis(CC), lymphocytic colitis (LC), and incomplete microscopic colitis and is caused by genetic alteration, immune dysregulation, or autoimmunity.^6,8 Furthermore, this disease also has a high prevalence in the elderly and causes them to have the symptoms of chronic watery and non-bloody diarrhoea.⁶
• Drug-induced colitis: Drugs like non-steroid anti-inflammatory drugs (ibuprofen, diclofenac, and naproxen etc), proton pump inhibitors ( omeprazole, lansoprazole, and esomeprazole etc ), beta-blockers (atenolol, bisoprolol and labetalol etc), aspirin, and statins may induce colitis.^6,9
• Radiation colitis: It could be related to pelvic radiotherapy for gynaecological
  (dealing with the health diseases of women), rectal and urological (urinary system) cancer.⁶

Diagnosis

Differentiation of the colitis types depends on a comprehensive examination in clinical practice including laboratory tests, multidetector CT, and colonoscopy or proto-sigmoidoscopy.⁶

• Laboratory test: A complete blood count test, liver function panel, and metabolic tests can help medical professionals understand patients' hemodynamic and biochemical status quickly. For ischaemic colitis, there is no specific marker to detect the disease but some elevated markers such as lactate, creatine kinase, CRP or amylase would indicate poor systemic circulation of patients.²
• Multidetector CT and thin sections: The CT can show precise inflammatory changes in the colonic wall so physicians would be able to collect more evidence before confirming the diagnosis, especially for Crohn's disease and ulcerative colitis differentiation.⁶
• Colonoscopy or proctosigmoidoscopy: Colonoscopy or proctosigmoidoscopy plays an important role in the colitis diagnosis differentiation. This is when a thin tubed camera is inserted into the intestinal tract via the rectum to visualise the inner walls of the intestines for damage. Images obtained can allow physicians to visualise the mucosal change and inflammatory locations in the colonic wall. Especially for ischaemic colitis, colonoscopy remains the most sensitive diagnostic tool.^3,6
• Electrocardiogram/echocardiogram: Ischaemic colitis may result from poor systemic perfusion and is highly related to heart disease, so transthoracic echocardiogram and electrocardiogram may be performed to assess heart function.⁶

Clinical presentation

In general, patients with colitis will present with symptoms including consistent or intermittent abdominal pain, abdominal bloating, bloody stools, dehydration, diarrhoea, fever, and constant urge to pass stools.⁹ The elderly population has a relatively high prevalence of ischaemic colitis. They usually present with bloody diarrhoea and leukocytosis with the initial onset of acute crampy abdominal pain.³ 

For inflammatory bowel disease, patients may have the symptoms of bloody or mucusy diarrhoea, abdominal pain, and a severe urge to pass stools.⁷ However, the location of abdominal pain is slightly different: Crohn's disease presents with right lower quadrant pain and ulcerative colitis presents with left lower quadrant pain.⁷ 

For infectious colitis caused by bacteria, patients present with similar symptoms as compared to presenting symptoms in other types of colitis like abdominal pain, diarrhoea, urge to pass stools and fever.¹ However, for infectious colitis caused by viruses, patients will have upper gastrointestinal symptoms such as nausea and vomiting.²  

Treatment

Different causes of colitis correspond to different therapies. There is no standard
treatment to apply for all different types of colitis. The general principle of colitis treatment is allowing bowel rest and hydration by administering intravenous fluid accordingly. Also, broad-spectrum antibiotic administration may be necessary if colonic inflammation is moderate or severe. 

In ischaemic colitis, if patients present with acute peritoneal pain or tenderness on palpation but are under stable hemodynamic status, it is recommended that these patients undergo an urgent colonoscopy to confirm the ischemic areas and inflammatory degrees.² If ischaemic colitis progresses to an infective condition like peritonitis or intestinal perforation, surgery may be involved.^{3, 6}  

Summary

Colitis is an inflammatory process of the colonic gut. The clinical presentations of diseases vary from disease-caused agents. The article has mainly introduced ischemic colitis, inflammatory bowel disease, and infectious colitis disease mechanisms. It could be poor perfusion in the colon, malfunctioning immune response, and bacteria or viral infection. Diagnosis justification relies on laboratory tests, multidetector CT, thin section, electrocardiogram, colonoscopy or proctor-sigmoidoscopy etc. 

In particular, colonoscopy plays a vital role in confirming the diagnosis of colitis types. The clinical symptoms of colitis may include abdominal bloating, bloody stools, dehydration, diarrhoea, fever and constant urge to pass stools. However, colitis with different aetiologies may have different clinical presentations and therefore require different clinical therapies. Providing the public with basic knowledge of ischemic colitis and other types of colitis can raise awareness of disease severity and potential treatments, prompting them to seek further assistance in hospitals before the condition deterioration.