Bowel symptoms · Patient guidance
Persistent watery diarrhoea: could it be microscopic colitis?
Why a normal-looking bowel may still need tissue samples.
In short
Persistent watery diarrhoea can have several causes. Microscopic colitis is one: the bowel lining may look normal during colonoscopy, while tissue samples reveal inflammation under a microscope.
- A normal-looking bowel does not, by itself, exclude microscopic colitis.
- Blood tests, stool tests and a medicine review help guide the investigation.
- Biopsies are useful when the symptoms and clinical assessment make this condition a possibility.
- Severe diarrhoea with dehydration or severe abdominal pain needs urgent medical care.
The colonoscopy report says the bowel looked normal, but you are still making urgent trips to the toilet. The next useful question is whether biopsies were taken, what they showed, and what else could explain the diarrhoea.
If you have not had a colonoscopy, your GP can help decide which tests are appropriate.
A normal appearance is useful information. It is not the same as checking the lining under a microscope. NIDDK explains why biopsies are needed to diagnose microscopic colitis.
Understanding microscopic colitis
Microscopic colitis is inflammation of the large bowel that is identified in small tissue samples. The main types are collagenous colitis and lymphocytic colitis. These names describe what the pathologist sees under the microscope.
It is a form of inflammatory bowel disease, but it differs from Crohn’s disease and ulcerative colitis. It is also different from irritable bowel syndrome, or IBS. Similar symptoms do not mean the conditions have the same cause or treatment. Crohn’s & Colitis Australia explains the condition and its types.
The usual symptom is ongoing watery diarrhoea without visible blood. Urgency, accidents, abdominal discomfort and diarrhoea that wakes you at night can occur. Symptoms may settle and then return. These features can suggest a need for further assessment, but they cannot diagnose microscopic colitis on their own. NIDDK describes the symptoms.
Why take biopsies if the bowel looks normal?
A colonoscopy shows the surface of the bowel. A biopsy answers a different question: what is happening within a tiny sample of that lining?
When microscopic colitis is suspected, samples are collected through the colonoscope and sent to a pathology laboratory. The laboratory report is separate from the immediate visual findings. Ask for both reports when reviewing an earlier procedure. NIDDK describes this diagnostic process.
The European microscopic colitis guideline recommends samples from at least the right and left sides of the colon. Sampling only the rectum is not sufficient to exclude it. A stool inflammation test called faecal calprotectin also cannot reliably rule it out. European microscopic colitis guideline.
This does not mean everyone needs biopsies or a repeat colonoscopy. The reason for the original test, the samples already taken and your current symptoms all matter.
Checks before another colonoscopy
Start with your GP and the pattern of your symptoms. Note when the diarrhoea began, whether it happens at night, any weight change, recent travel and recent antibiotics. Bring previous test results and a complete list of medicines and supplements.
Assessment may include blood tests, coeliac testing and stool tests for infection. The choice depends on your history. Queensland Health asks GPs to include your symptoms and previous results in a referral. This helps the specialist decide which tests you need. Queensland Health diarrhoea guidance.
If coeliac testing is planned, keep eating gluten until testing is complete. Starting a gluten-free diet beforehand can make the results inaccurate. Tell your doctor if you have already changed your diet. Coeliac Australia diagnostic guidance.
Persistent diarrhoea deserves assessment even if an earlier test was reassuring. The broader guide to changes in bowel habits explains how accompanying symptoms affect the next step.
Medicines that may be contributing
The European guideline reports links between microscopic colitis and some medicines, including anti-inflammatory painkillers, acid-reducing medicines called proton pump inhibitors, and some antidepressants. A link does not prove that a medicine caused the condition in one person.
Timing can be helpful: did symptoms start after a medicine was introduced or changed? Your prescriber can weigh this against why you need the medicine and whether an alternative is appropriate. Do not stop prescribed medicines yourself. The European guideline distinguishes medicine associations from causation.
Include medicines bought without a prescription in the discussion. Bring the packets or an up-to-date list if the names are difficult to remember.
Treatment after a confirmed diagnosis
The next step is a treatment plan based on symptom severity, other conditions and your medicines. Treatment often involves medication; budesonide is commonly used. Your treating clinician explains the expected benefits, possible adverse effects and follow-up. A diagnosis does not mean surgery is the usual treatment. NIDDK treatment information.
Diet changes may help particular symptoms, but no diet has been shown to heal microscopic colitis. Restricting several food groups without guidance can make eating harder without answering the underlying question. A dietitian can help where food triggers, lactose intolerance or another diagnosed condition need attention. NIDDK diet and nutrition information.
Before leaving the results appointment, ask who will oversee treatment and how to arrange review if symptoms persist or return. Keep a copy of the pathology report with your procedure report.
When does diarrhoea need urgent care?
Seek urgent medical attention for severe diarrhoea, dehydration, heavy rectal bleeding, or diarrhoea with severe abdominal pain. Dehydration can cause a dry mouth, marked thirst and reduced urination. Go to an emergency department if you are seriously unwell; call 000 in a medical emergency.
Arrange medical review for ongoing diarrhoea, blood or mucus in the stool, fever, unexplained weight loss or diarrhoea at night. Do not wait for a routine endoscopy appointment if your condition is worsening. Healthdirect guidance on diarrhoea and urgent care.
How can Colonoscopy Brisbane help?
Colonoscopy Brisbane provides assessment and endoscopic investigation of bowel symptoms. If a colonoscopy is appropriate, tissue samples may help investigate the cause of your diarrhoea. The results are considered alongside your symptoms and earlier tests.
For an appointment with Dr Goutham Sivasuthan, bring your referral, medicine list, stool and blood results, and any previous colonoscopy and pathology reports. This helps make the consultation useful even if your earlier procedure was elsewhere.
Read about the colonoscopy service or contact the team about a referral. Further testing depends on the assessment; a consultation does not automatically lead to another scope.
Frequently asked questions
Can I have microscopic colitis with a normal colonoscopy?
Yes. The bowel can look normal while biopsies show microscopic colitis. Check whether your earlier investigation included appropriate samples and a pathology report before assuming the condition was excluded.
Does watery diarrhoea always mean microscopic colitis?
No. Infection, coeliac disease, medicines and other conditions can cause similar symptoms. Your history and selected tests help distinguish them.
Should I request a repeat colonoscopy straight away?
Not automatically. Ask your treating clinician to review the original procedure and biopsy reports first. The decision depends on what has already been assessed and what has changed.
Can I manage it by changing my diet?
Diet changes may ease symptoms, but they do not replace diagnosis or the treatment plan for confirmed microscopic colitis. Avoid starting a gluten-free diet before any planned coeliac testing is complete.
This article provides general information for adults and does not replace individual medical advice or your treating team’s instructions.
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