HIV associated diarrhoea

The broad differential diagnosis for HIV associated diarrhoea includes:
1. Bacterial infections (Salmonella, Shigella, Campylobacter)
2. Parasitic infections (Cryptosporidium, Isospora, Giardia, Microsporidia, Entamoeba histolytica)
3. Mycobacterial infections (Mycobacterium avium complex (MAC), Mycobacterium tuberculosis)
4. Viral infections (Cytomegalovirus)
5. Drug-associated diarrhoea (e.g. nelfinavir)
6. Idiopathic diarrhoea (HIV enteropathy).

CMV colitis is uncommon in patients who are not severely immunocompromized. GI tract involvement may occur alone or in the setting of disseminated disease. CMV has three major patterns of infection: primary infection (in the immunocompetent host causing few or no symptoms; after initial infection, latent viral infection occurs), secondary reactivation (patients seropositive with latent infection who reactivate because of immunodeficiency) and superinfection. Within the colon, ulcerative changes may be seen and watery diarrhoea can develop. As ulcers increase in depth, erosion into blood vessels may cause profuse bloody diarrhoea. Inflammatory polyps do develop, which, rarely, obstruct the colon. Severe inflammation and vasculitis sometimes leads to ischaemia and transmural necrosis, with subsequent perforation and peritonitis. Classically findings on microscopy include giant cells with large ovoid or pleomorphic nuclei containing basophilic inclusions (owl's eyes).