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Microscopic Colitis

Microscopic colitis is discovered in about 10% of patients who have undergone colonoscopy for chronic diarrhoea.
Diagnosis is based on histological biopsy samples collected during a colonoscopy.
The most common subtypes: collagenous colitis and lymphocytic colitis
Aetiology and pathogenesis are unknown.
A benign disease, varied clinical course, medication only if necessary

Incidence about 10 new cases/100 000 person years
- More common in women than in men
Occurrence is more common after the age of 50 years and increases with age, but the disease may also occur in children.

Colonoscopy
- The endoscopic view often has a normal appearance.
- Tissue biopsies must always be taken if diarrhoea is the principal symptom.
Histological analysis will reveal, among other things, inflammatory changes in the lamina propria and degeneration of the epithelium.
- Collagenous colitis: thickened subepithelial collagen layer
- Lymphocytic colitis: increase in the number of intraepithelial cells, mainly lymphocytes
- Inflammatory changes throughout the entire large bowel, most markedly at its start and midsection, sometimes also in the ileum
Laboratory investigations are those used in the basic examination of any patient with diarrhoea; see also article Prolonged diarrhoea in the adult Prolonged Diarrhoea in Adults.
- Basic blood count with platelet count, ESR, CRP, sodium, potassium, creatinine
- Thyroid-stimulating hormone (TSH), transglutaminase antibodies
- Faecal calprotectin normal or elevated

Differential diagnosis of chronic non-bloody diarrhoea (see Prolonged Diarrhoea in Adults)

The incidence of autoimmune diseases is high among patients, particularly coeliac disease must be excluded
Rheumatic conditions, collagenosis, different pain syndromes, fibromyalgia
Possible link with medicines: aspirin, other NSAIDs, proton pump inhibitors (PPI) or H₂-receptor blockers; SSRIs

Symptomatic; regular medication is often not needed
Dietary advice as for irritable bowel syndrome (IBS) Functional Bowel Disorders and the Irritable Bowel Syndrome (IBS).
Dietary fibre may be beneficial in mild disease forms.
Loperamide: on a regular basis or as needed, high enough dose

Cholestyramine is effective in some patients even in the absence of co-existing bile acid malabsorption: (½-1 sachet 1-3 times daily)
- The patient may try stopping the medicine during an asymptomatic phase
- Note! Cholestyramine affects the absorption of other medicines
Glucocorticoids (bear the adverse effects in mind)
- Budesonide SIR
  - Administered as a course with gradually decreasing doses
    - E.g. 9 mg for 1-2 months, 6 mg for 1-2 months, 3 mg for 1-2 months
  - Best proven efficacy, but the symptoms often recur when the medication is discontinued
- Budesonide MMS
  - Budesonide is released in the colon.
  - Used in ulcerative colitis
  - Evidence is so far lacking for the use in microscopic colitis.
- Courses of prednisolone if the above medication proves ineffective
- 5-ASA medications as in ulcerative colitis
  - Mesalazine or sulphasalazine
  - Will help about 50% of the patients.
  - Medication can be stopped in an asymptomatic phase.
Sometimes azathioprine, methotrexate, TNF-alpha inhibitors
- In the presence of very severe symptoms, continual need for glucocorticoids; in specialist care!
National legislation as regards the reimbursement of medicines applies.

The prognosis is good.
- Spontaneous remissions and several years with no symptoms are possible
Not known to increase the risk of, for example, bowel cancer.
- No need for endoscopic follow-up
Evaluation and management by a specialist is indicated if the symptoms are troublesome and the patient needs repeated courses of budesonide.