Overview
Microscopic colitis is a common but under-recognised cause of chronic, watery, non-bloody diarrhoea, particularly in middle-aged and older adults. Despite causing significant symptoms, the colon appears completely normal on colonoscopy — the diagnosis is made only on microscopic examination of mucosal biopsies. There are two histological subtypes: collagenous colitis (characterised by a thickened subepithelial collagen band) and lymphocytic colitis (excess intraepithelial lymphocytes). It is strongly associated with NSAID use, proton-pump inhibitors (particularly lansoprazole), and certain antidepressants. Budesonide is the most effective treatment.
Symptoms
Chronic watery, non-bloody diarrhoea — often 5 to 15 loose stools per day
Nocturnal diarrhoea (waking from sleep to have diarrhoea — an important alarm feature)
Faecal urgency and, occasionally, incontinence
Abdominal cramping and bloating
Fatigue and unintentional weight loss during active disease
Common Causes
NSAIDs (aspirin, ibuprofen, naproxen, diclofenac) — one of the strongest modifiable risk factors
Proton-pump inhibitors, particularly lansoprazole and omeprazole
Certain antidepressants (SSRIs: sertraline, paroxetine; SNRIs)
Autoimmune tendency — frequently co-exists with coeliac disease, thyroid disease, and rheumatoid arthritis
Smoking — increases risk and worsens disease course
Self-Care Tips
Stop all NSAIDs and review every current medication with your doctor — removing the causative drug alone can lead to full remission
Avoid caffeine, alcohol, and high-fat foods which worsen diarrhoea during active disease
Stay well hydrated — chronic watery diarrhoea causes significant fluid and electrolyte loss
Budesonide (a topical oral corticosteroid) is the evidence-based first-line treatment — take as prescribed for the full course (usually 6–8 weeks)
Maintain a follow-up schedule — microscopic colitis can relapse and some patients require long-term low-dose maintenance therapy
Get tested for coeliac disease if not already done — it co-exists in approximately 10% of microscopic colitis patients
When to See a Doctor
Any chronic watery diarrhoea lasting more than 4 weeks warrants colonoscopy with biopsies taken from multiple segments even if the bowel looks normal — the diagnosis of microscopic colitis cannot be made without biopsy. Nocturnal diarrhoea, significant weight loss, or dehydration should prompt urgent assessment.
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