Overview

On average, it takes two to three years to accurately diagnose irritable bowel disease (IBD) and irritable bowel syndrome (IBS) in a patient.¹ While IBD is the chronic inflammation of the gastrointestinal (GI) tract,² IBS instead is a functional disorder of the GI tract.³ Since they share many symptoms, they are often mistaken for one another. 

A recent case-control study showed that IBD patients are three times more likely to be previously misdiagnosed or treated for IBS.⁴ A misdiagnosis of IBD can be harmful, as it prevents a patient from getting the proper healthcare they need to reduce the symptoms and complications that arise from the inflammation. Untreated IBD prolongs damage to the digestive system, increasing the risk of colon cancer.⁵ Hence, a more detailed comparison of the two medical conditions will be made to better identify the symptoms and risk factors of IBD and IBS.

IBD

As mentioned previously, IBD is classified as an inflammatory disease of the GI tract. While the exact cause of IBD is still unknown, its effect leads to dysbiosis of the gut microflora.⁶ Dysbiosis refers to the imbalance between gut microorganisms (primarily bacteria). Bacteria and humans have a symbiotic relationship: while we give these beneficial bacteria a nutrient-rich environment to survive, they return the favour by preventing the colonisation of harmful bacteria and supporting the digestion of our meals.⁷ An imbalance in this harmonious composition of gut microorganisms can cause damage to the intestinal barrier. Since a damaged intestinal barrier leads to the invasion of harmful microorganisms,⁸ it is widely theorised why an inappropriate immune response is triggered. IBD comprises two types of disease: Crohn’s disease and ulcerative colitis.

Crohn’s disease

American gastroenterologist Burrill B. Crohn and his colleagues distinguished Crohn’s disease from the frequently overdiagnosed intestinal tuberculosis in 1932.⁹ Similarly to ulcerative colitis, incidence and hospitalisation of Crohn’s disease has been the most common in the northern latitudes of Europe and America.¹⁰ Recent decades have however shown a particular increase in incidence in Asia and Africa, likely due to environmental changes from industrialisation.¹¹ 

Though this is a leading theory, understanding the risk factors of the disease can better aid prevention and diagnosis. A person has a 25-40% higher risk if they have a family history of Crohn’s disease; smoking can increase the incidences of flare-ups; it is likely for someone to develop the disease following infectious gastroenteritis; and for the first five years post-operation, appendicectomy can increase the risk of Crohn’s disease.¹² What makes Crohn’s disease different to ulcerative colitis is that chronic inflammation presents itself throughout the gut and on the entire thickness of its lining, developing ulcers from the mouth to the anus, compared to ulcerative colitis where inflammation occurs only in the colon.¹³ As a result, the symptoms are widely spread and can vary in severity. The core symptoms are:

• Diarrhoea
• Cramping and abdominal pain
• Weight loss

However, the following can also manifest in Crohn’s disease:

• Anaemia
• Red eyes or eye pain
• Fatigue
• Fever
• Nausea or loss of appetite
• Joint pain or soreness
• Red and tender bumps under the skin¹⁴

Ulcerative colitis 

As described by the President of the Royal College of Physicians Sir Samuel Wilk in 1875,¹⁵ ulcerative colitis is the chronic inflammation and ulceration that occurs strictly in the colon on the gut's inner lining.¹⁶ Though Crohn’s disease is more common among IBD cases, it still affects approximately five million people worldwide,¹⁷ with a predominant occurrence in adults.¹⁸ Areas where distinct differences have been found between ulcerative colitis and Crohn’s disease include the risk factors and symptoms. Despite the family history and use of non-selective non-steroidal anti-inflammatory drugs also increasing the risk of ulcerative colitis, the risk instead significantly decreases for those who do smoke or have not had an appendicectomy.¹⁹ Nonetheless, this should be taken with caution as stopping smoking is still recommended when weighing the benefits and risks. Interestingly, isolating the components of tobacco products, especially nicotine,²⁰ has become a conversation starter for its potential use in IBD therapy. In regards to the symptoms, the following is most commonly observed:

• Recurring diarrhoea
• Blood in stool or rectal bleeding 
• Mucus or pus in stool 
• Abdominal pain, particularly when passing stool
• Frequent urge to have a bowel movement- even if it's empty

More severe cases may include:

• Fatigue
• Fever
• Nausea or vomiting 
• Weight loss²¹

IBS

While IBD and IBS share some similar symptoms, the pathophysiology is fundamentally different between the two. IBS is defined as the abnormal function of the GI tract; though the cause of IBS is also unknown, dysbiosis is also considered a possible theory. 

Specific to IBS, it is suspected that stress and other physiological factors can cause dysbiosis. There is a bidirectional signalling network between the brain and gut (mostly referred to as the gut-brain axis) that connects the emotional and cognitive aspects of the brain to the functionality of the gut.²² A stressful event can possibly cause changes in the gut microbiota composition and decrease in the threshold for pain in the intestines (visceral hypersensitivity).²³ This causes people with IBS to feel heightened pain or discomfort where their intestines are.

According to the National Institute of Diabetes and Digestive and Kidney Diseases, women are two times more likely to have IBS than men. Other risk factors include people under the age of 50 years, family history of IBS, stressful life events, and severe infection in the digestive system.³ Like in ulcerative colitis, IBS is more prevalent in non-smokers than smokers.²⁴ However the evidence for this is less conclusive, as the study was carried out in one country. 

Though the global prevalence of IBS is high, it is highest in South America.²⁵ Similarly to IBD, there is a strong correlation between IBS and industrialisation. Industrialisation leads to changes in dietary consumption, stressful lifestyle changes, and pollution - all of which may adversely affect gut health.¹ IBS is split into three categories that are categorised by the core symptoms: IBS-constipation (IBS-C), IBS-diarrhoea (IBS-D), and IBS-mixed (IBS-M).

IBS-C vs IBS-D vs IBS-M

An American study has shown that people with constipation-predominant IBS are more likely to feel self-conscious and have difficulty concentrating than those with diarrhoea-predominant IBS.²⁶ However, people with diarrhoea-predominant IBS have been shown in the same study to avoid going outdoors, especially if there is no bathroom. Both types of IBS have significant negative impacts on day-to-day activities, reducing their quality of life. Alongside recurrent abdominal pain/ discomfort, people are diagnosed with one of the three types of IBS in accordance with the Bristol Stool Scale (BSS):

• IBS-C: BSS 1 or 2 for at least a quarter of bowel movements 
• IBS-D: BSS 6 or 7 for at least a quarter of bowel movements 
• IBS-M: at least 25% of bowel movements of 1-2 and 6-7 each²⁷

Additional symptoms include: 

• Bloating, exacerbating abdominal pain/ discomfort
• Increased flatulence 
• Mucus in stool
• Fatigue 
• Nausea 
• Backache
• Bowel incontinence²⁸

Summary

Distinguishing IBD and IBS from each other may be difficult as they present similar symptoms (i.e. diarrhoea, abdominal pain, fatigue, nausea and changes in stool) and both are likely due to dysbiosis in the gut. However, they each have their unique characteristics that are crucial to identify during diagnosis. While IBD involves chronic inflammation, IBS presents an array of hypersensitivity-related symptoms. Also, each have their subtypes that are distinct from each other. Crohn’s disease presents inflammation and ulcers anywhere from the mouth to the anus, whereas they are restricted to the colon in ulcerative colitis. A proper medical and family history and clinical evaluation are key to preventing misdiagnosis. Whether they need specific drugs or changes in their diet, patients can receive the appropriate treatment for their GI-related medical condition.