Introduction

Inflammatory bowel disease (IBD) is a medical term describing chronic inflammatory disorders that affect the gastrointestinal (GI) tract.¹ IBD involves the inflammation of the GI tract caused by an abnormal immune response to the guts microbiome.² This can include long lasting diarrhoea, stomach pains, blood or mucus in your stool, rectal bleeding, fatigue and unexplained weight loss.¹

There are two main types of IBD: Crohn’s disease (CD) and ulcerative colitis (UC).¹ CD is an inflammatory disease that can affect the entire GI tract, causing it to become swollen and irritated.² It can also cause the bowel wall to thicken in a process called transmural inflammation.² UC is another chronic inflammatory bowel disease caused by an abnormal immune response and causes inflammation of the inner lining of the large intestines. 

Coeliac disease is a disease where there is an abnormal immune response to the small intestine when gluten is consumed.³ The immune system causes damage to the gut, which causes nutrients to not be absorbed into the body.

The gastrointestinal (GI) tract is an important part of the digestive system and the organs include:⁴

• Mouth - chewing of the food
• Pharynx - tube in the neck that is important in digesting the food 
• Oesophagus - tube that joins the pharynx to the stomach and where the food travels when swallowed
• Stomach - organ responsible for digesting the food using enzymes and acids to break down the food to enter the small intestines
• Small intestine - receives digested food from the stomach, further breaks it down using enzymes whilst absorbing nutrients from the food into the body and discarding the waste
• Large intestine (gut), whose function is to absorb water from the undigested food, to remove waste from the body and to form faeces 
• Rectum - is where faces are collected until it's ready to leave, and it also absorbs water
• Anus is the opening where stool passes out of the body

It is important to understand IBD and coeliac disease as they affect millions of people all around the world. As they are both chronic diseases, they place a significant burden on the healthcare systems globally whilst simultaneously affecting the patients quality of life. 

Inflammatory Bowel Disease (IBD)

Overview and prevalence

As described earlier, IBD is the inflammation of the GI tract caused by an abnormal immune response to the gut microbiome.² There are two types of IBD - CD and UC that differ in the location of where inflammation occurs in the GI tract and the depth of bowel wall inflammation.² CD can affect the entire GI tract from the mouth to the anus but it mostly affects the small and large intestine, whilst UC causes inflammation of the colon and rectum.² Both CD and UC can be categorised by their severity (mild, moderate and severe) and where it is located.² 

IBD prevalence was found in 321 patients per 100,000 population in 2021 and this has increased substantially from 2006 where the prevalence was 200 individuals per 100,000 population.⁵ IBD is more prevalent in the North American and European populations than in Africa or Asia.² IBD occurs most commonly in individuals aged 15 to 30 years old, with 25% of patients developing IBD during adolescence.² IBD is more common in developed countries and where the climate is colder.² 

Aetiology

The cause of IBD is not fully understood as there is no universal cause present in all patients.^1,2 

Genetics is a factor that plays an important role in developing IBD. CARD15 gene is associated with IBD and this gene is responsible for regulating apoptosis which is an important element in the immune response that causes cell death to occur.² CARD15 gene is more important in CD compared to UC.² In some patients, the gene NOD2 is mutated causing dysregulation in the GI immune system.⁶ This causes the immune system to incorrectly target the microbiome in the gut, causing inflammation.⁶

The environment is a trigger that can cause IBD to develop.⁶ A popular theory is the hygiene hypothesis where autoimmune diseases such as IBD are caused by a lack of exposure to pathogens when we were younger due to an improvement in sanitation.⁶ This can lead to specific environmental triggers that can lead to IBD and these include:

• Smoking: the relationship between smoking and IBD is not fully understood but tobacco is a known causation. Active smokers are less likely to develop UC compared to non-smokers and ex-smokers but the opposite is true in developing CD^2,6
• Oral contraceptives pill: IBD is thought to develop using contraceptive pills due to the effect of oestrogen⁶
• Appendectomy: is the surgical removal of the appendix and is negatively associated with UC but an increased risk of developing CD⁶ 
• Diet: diet is considered a risk of developing IBD but the specifics are not fully known. Some studies show that a diet high in sugar and saturated fats is associated with the development of IBD⁶
• Breastfeeding: reduces the chance of infants developing IBD compared to formula-only babies.⁶ This is due to breastfeeding providing the infant with important healthy microbes and important antibacterial and anti-inflammatory properties⁶
• Non-steroidal anti-inflammatory drug: can cause direct damage to the mucus layer of the GI tract⁶

Pathophysiology

The intestinal immune system is the main cause of IBD. Usually, the intestine epithelial cells protect pathogens from entering the GI tract and causing infection. However, during IBD, the excessive inflammation destroys the lining barrier.² An abnormal immune response triggered by the guts microbiome is responsible for the inflammation which leads to tissue damage in the GI tract, causing symptoms to appear.

Clinical presentation

Symptoms of IBD includes:¹

• Diarrhoea associated with blood or mucus
• Abdominal pain
• Rectal bleeding
• Nausea and vomiting
• Weight loss
• Fatigue

Diagnosis

IBD is diagnosed through a combination of clinical history, medical images and laboratory diagnosis.⁷

Patient history is first taken and symptoms understood to rule out other bowel diseases.

To detect Crohn’s disease, endoscopy is used and for ulcerative colitis, colonoscopy is used. Other imaging tools are used like:

• Contrast tomography 
• MRI
• CT

Laboratory diagnosis includes using stool tests and blood tests.⁷

Treatment

Each treatment of IBD will depend on the severity of the patient and the aim of the treatment is to reduce the inflammation in both CD and UC.²

For CD, there is no cure and treatment is based on preventing the symptoms from returning. Medicines are the usual treatment and these include:

• Aminosalicylates: used to treat mild to moderate UC and CD and works by preventing inflammation
• Corticosteroids: anti-inflammatory medicines
• Immunomodulators such as methotrexate; reduces immune response which reduces inflammation.
• Biologics therapies like TNF alpha blockers

Surgery is used to remove the damaged tissues in the GI tract.⁷

Coeliac disease

Overview

Coeliac disease is an autoimmune disease triggered by gluten that causes inflammation in the small intestines.⁸ The prevalence of coeliac is between 0.5 to 1% of the population but its prevalence is increasing more each year despite coeliac being underdiagnosed.^8,9 Coeliac disease is more common in patients with other autoimmune diseases such as type 1 diabetes and autoimmune thyroid disease.⁸

Etiology

Coeliac disease is caused by an abnormal immune response to gluten which is a protein found in nature. Individuals with HLA-DQ2 or DQ8 genes are more susceptible to developing coeliac disease, as the genes encode proteins that present gluten to the immune system, marking gluten as a foreign material and initiating the immune response.¹⁰ 

Pathophysiology

Damage occurs to the small intestine due to a protein in gluten called gliadin which causes inflammation in the small intestine.⁸ The inflammation causes tissue damage in the small intestine which prevents nutrition absorption.⁸ This leads to poor health of the individuals.

Symptoms

Symptoms of coeliac disease can vary in severity and these include:³

• Diarrhoea
• Abdominal pain
• Stools with high level of fat
• Bloating
• Indigestion
• Constipation
• Vomiting
• Fatigue
• Unexplained weight loss
• Infertility
• Itchy rashes
• Malnutrition

Diagnosis

Diagnosis for coeliac will first include taking a family history followed by a blood test that measures gluten antibodies in the blood.³ If the blood test is positive, doctors may also request for a biopsy of the small intestine. Before testing, patients will be told to eat gluten to get an accurate testing.³ 

Treatment

Coeliac patients are recommended to eat a strict gluten-free diet. By excluding gluten from your diet, more tissue damage is prevented, which alleviates symptoms such as diarrhoea. This however is a life-long diet but specialists are available to help make the transition easier.³

Comparison and contrast

Similarities between IBD & coeliac disease

1. Both IBD and coeliac disease are chronic inflammatory diseases within the GI tract. The chronic inflammation is responsible for their symptoms such as diarrhoea, abdominal pain, and fatigue for both medical conditions
2. Both diseases are caused by an abnormal autoimmune response which causes the immune system to target healthy tissue cells which initiates inflammation, leading to further damage of the GI tract

Differences between IBD & coeliac disease

1. IBD and coeliac disease differ in the location of the GI tract they affect. IBD (Crohn’s) affects the entire GI tract from the mouth to the anus whilst coeliac disease is more localised at the small intestine
2. The triggers for the disease also differ. In IBD, there are several reasons that cause the immune response to target the gut microbiome, which causes inflammation and tissue damage. However, in coeliac disease, an autoimmune response is triggered in response to gluten which is found in food, which damages the small intestine, preventing nutrients absorption

Summary

IBD is the inflammation of the GI tract caused by an abnormal immune response to the gut microbiome.² There are two types of IBD, CD and UC which are characterised by the GI tract and the depth of bowel wall inflammation. Coeliac disease is an autoimmune disease triggered by gluten that causes inflammation in the small intestines.⁸ 

Both of these medical conditions are chronic inflammatory diseases that affect the GI tract caused by an abnormal immune response that mistakenly targets healthy tissue causing damage to the GI tract. The damage to the GI tract is responsible for the symptoms experienced by the patients. It is important to understand the difference between IBD and coeliac disease to properly manage patient symptoms, prescribe correct treatments, and to improve patient care. There is no cure for either IBD and coeliac disease, and properly managing the disease is crucial for improving patients' quality of life.