[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Gastrointestinal tract](https://durgical.com/en/general-pathology/areas/gi/) › Other colitis: microscopic, diversion, GVHD, drug

# Other colitis: microscopic, diversion, GVHD, drug

- Lesion

Several kinds of colitis cause diarrhoea with a normal-looking colon; only the biopsy reveals collagen bands, lymphocytes or dying cells.

Updated Nov 12, 2026

## Key points

- Diversion colitis: numerous mucosal lymphoid follicles in a bypassed segment; short-chain fatty acids from bacteria are missing; resolves when flow is restored.
- Collagenous colitis: thick subepithelial collagen band plus intraepithelial lymphocytes; mostly middle-aged and older women.
- Lymphocytic colitis: normal collagen, many intraepithelial lymphocytes; linked to coeliac disease and autoimmunity; NSAIDs and perhaps proton pump inhibitors can cause similar change.
- Both forms of microscopic colitis: chronic non-bloody watery diarrhoea without weight loss; endoscopy normal.
- Graft-versus-host disease: donor T cells; crypt-cell apoptosis with sparse lymphocytes, crypt dropout in severe cases.
- Checkpoint-inhibitor and mycophenolate colitis mimic graft-versus-host disease.

## What it is

Some forms of colitis are defined mainly by histology. Diversion colitis develops in a segment bypassed by an ostomy. Microscopic colitis (collagenous and lymphocytic) causes chronic watery diarrhoea with a normal endoscopy. Graft-versus-host disease and apoptotic colitis from drugs such as immune checkpoint inhibitors and mycophenolate are marked by epithelial apoptosis.

## Histology-defined colitides

| Type | Setting | Key histology | Endoscopy |
| --- | --- | --- | --- |
| Diversion colitis | Segment bypassed by an ostomy | Many mucosal lymphoid follicles | Red, friable |
| [Collagenous colitis](https://durgical.com/en/conditions/microscopic-colitis/) | Older women | Thick subepithelial collagen plus intraepithelial lymphocytes | Normal |
| [Lymphocytic colitis](https://durgical.com/en/conditions/microscopic-colitis/) | Coeliac disease, autoimmunity, drugs | Many intraepithelial lymphocytes, normal collagen | Normal |
| [Graft-versus-host disease](https://durgical.com/en/conditions/graft-versus-host-disease/) | After allogeneic stem cell transplant | Crypt apoptosis, crypt loss, sparse infiltrate | Variable, may be normal |
| Apoptotic (drug) colitis | Checkpoint inhibitors, mycophenolate | Increased epithelial apoptosis | Variable |

## Clinical notes

- Chronic watery diarrhoea with a normal colonoscopy calls for random biopsies.
- Checkpoint-inhibitor colitis may be severe enough to stop cancer treatment.

## Memory aid

Diverted: follicles. Collagenous: a pink band. Lymphocytic: a crowd of lymphocytes. GVHD and drugs: dying crypt cells.

## Test yourself

Think of the answer, then tap the question to see it.

## What defines collagenous colitis histologically?

A thickened subepithelial collagen band with increased intraepithelial lymphocytes and lamina propria inflammation.

## What is the most common histological finding in intestinal graft-versus-host disease?

Epithelial apoptosis, especially of crypt cells, with relatively sparse inflammation.

## Why does diversion colitis resolve after the ostomy is closed?

Faecal flow returns, restoring nutrients such as bacterial short-chain fatty acids to the colonocytes.

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## Elsewhere in DurgiPedia

- [Graft-versus-host disease](https://durgical.com/en/immunology/graft-versus-host-disease/)

## Connections

## Related 5

- [Ulcerative colitis vs Crohn disease](https://durgical.com/en/general-pathology/ulcerative-colitis-vs-crohn-disease/)
- [Coeliac disease](https://durgical.com/en/general-pathology/coeliac-disease/)
- [Ischaemic bowel disease](https://durgical.com/en/general-pathology/ischaemic-bowel-disease/)
- [Apoptosis: the intrinsic and extrinsic pathways](https://durgical.com/en/general-pathology/apoptosis-the-intrinsic-and-extrinsic-pathways/)
- [Injury by therapeutic drugs: the classic examples](https://durgical.com/en/general-pathology/injury-by-therapeutic-drugs-the-classic-examples/)

## Related conditions 3

- [Microscopic colitis](https://durgical.com/en/conditions/microscopic-colitis/)
- [Graft-versus-host disease](https://durgical.com/en/conditions/graft-versus-host-disease/)
- [Coeliac disease](https://durgical.com/en/conditions/coeliac-disease/)

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Ulcerative Colitis](https://www.ncbi.nlm.nih.gov/books/NBK459282/) (StatPearls (NCBI Bookshelf), 2025).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/general-pathology/other-colitis-microscopic-diversion-gvhd-drug/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/other-colitis-microscopic-diversion-gvhd-drug/