Chronic diarrhoea: causes, tests and treatment

It can be really unpleasant living with a bout of diarrhoea where you frequently have loose, watery stools. Symptoms usually resolve on their own without the need to see a doctor, however, if you’re experiencing chronic diarrhoea (lasting four weeks or more), it might be a symptom of an underlying condition such as irritable bowel syndrome (IBS).

We’ve asked one of our highly-experienced gastroenterologists, Dr Ian Johnston, to explain the possible underlying causes of diarrhoea and how he would work with his patients to devise a treatment plan.

What is chronic diarrhoea?

Different definitions of chronic diarrhoea exist. From a medical viewpoint, there are two main definitions. The most commonly used definition is from a perspective of the patient's symptoms and is defined as three or more loose stools (of Bristol stool form 6 or 7) for three months or more. The Bristol stool chart is a widely used visual tool which allows patients and medical professionals to characterise their stool.

The other main definition is based on stool weight and is defined as more than 200g of stool per day. From a pragmatic point of view, I tend to define it as troubling, loose stool of a few times a day going on for a number of weeks.
 

What are the common underlying causes of diarrhoea?

It is important to remember that everybody gets diarrhoea from time to time and to a certain degree it can be part of everyday life. Diarrhoea is one of the body’s ways of preventing or eliminating infection from the body. We all know that if we eat a hot curry or other spicy food that we may occasionally get diarrhoea the following day due to the spices.

It is not, however, common or normal to have diarrhoea every day and features such as faecal incontinence are of course abnormal and should not be tolerated. These would usually need to be investigated further. 

The commonest causes of diarrhoea include infections which may be viral or bacterial. Common viral infections include Norovirus, which is usually associated with vomiting. Other common infections may result from infected food sources such as poorly cooked chicken and common bugs are salmonella, shigella and Campylobacter.

Some people have diarrhoea associated with cramping abdominal discomfort, especially associated with stress. If the patient is otherwise well with normal basic investigations such as blood tests and with no weight loss, this is suggestive of a diagnosis of irritable bowel syndrome (IBS). 

Often further tests are required to confirm this diagnosis, however. A recently recognised entity is that of bile acid diarrhoea (BAD) which could otherwise be misdiagnosed as irritable bowel syndrome. This is a disorder in the processing of bile acids and can lead to troubling diarrhoea multiple times per day which can go on for months and years. A specialised test called a SeHCAT test is required to diagnose this.

There are some other potentially serious causes of diarrhoea which should be considered especially if there is weight loss, rectal bleeding or if it occurs in later life. Bowel cancer should always be excluded in that setting and this can be done using a colonoscopy or CT scan. In other situations, one has to consider diagnoses of inflammatory bowel disease such as Crohn's disease and ulcerative colitis.
 

What tests are used for diarrhoea?

Simple tests are usually conducted by the general practitioner and include blood and stool tests to exclude infection. Other stool tests can be done to look for inflammation within the bowel.

Once referred to secondary care, tests that are considered include colonoscopy, CT or MRI scans and nuclear medicine scans such as a the SeHCAT scan. Colonoscopy is most useful for investigating diarrhoea as it allows direct rectal observation of the bowel lining. It allows exclusion of polyps and cancers and also allows for biopsies for further microscopic examination. 

CTs and MRIs have the advantage of being non-invasive however biopsies cannot be taken. Further specialised tests such as the SeHCAT test are used in specific clinical circumstances.
 

How would you work with a patient to devise a treatment plan?

The first part of any consultation is taking a thorough history. This involves asking detailed questions to find out when the diarrhoea started and if there are any other associated features such as blood loss, weight loss or fever. I would also find out more about the patient's past medical history, including if they are taking any medications and if they have any allergies.

It is crucial to take patient’s views into consideration especially if they have a particular condition that they would like to be investigated, or if they are particularly keen on a particular test, or if they would like to avoid a certain test. I would discuss with the patient the likely diagnoses what tests need to be done. 

Often tests have already been conducted or no further tests need to be done, in which case one can proceed to medical treatment. If further tests are required I would discuss these with the patient including the pros and cons of each.
 

What lifestyle changes would you recommend?

Certain lifestyle changes can be useful in the treatment of diarrhoea, depending on the cause. It is crucial for the doctor and patient to have a clear diagnosis or at least a clear path towards diagnosis through the use of tests.

Lifestyle changes which may be helpful will depend on the diagnosis. For instance, in diarrhoea predominant irritable bowel syndrome (IBS-D) certain dietary modification may be helpful. Some people find the exclusion of gluten helpful even in the absence of coeliac disease.

Some patients may have lactose intolerance which can be tested for using a breath test and they will of course benefit from a lactose-free diet. Usually, the reduction of dietary fibre can be helpful, but not in all cases. Other dietary or lifestyle factors must also be considered such as caffeine intake, smoking and consuming sugar-free fizzy drinks or chewing sugar-free gum.



Dr Johnston specialises in treating acid reflux, IBS, diarrhoea and he offers expert guidance in nutrition. You can book a first consultation using video call and our e-Consultation tool on his profile here.