Lymphoma

Lymphoma occurs more often in HIV positive patients, particularly in those with advanced HIV disease. Most lymphomas are B cell in origin and are of high grade. Intrathoracic disease most frequently occurs in the context of disseminated disease.

Microsporidia are also an important cause of diarrhoea as well as being associated with hepatitis, peritonitis, sclerosing cholangitis, sinusitis, and renal failure. Diagnosis is difficult as the spores are only 1-5μm in diameter. A number of centres have reported successful identification of spores in stool using trichrome and fluorescent stains but morphology is best determined using electron microscopy. Albendazole has shown promise in AIDS patients with microsporidiosis but may only be active against Encephalitozoon intestinalis and not Enterocytozoon bienusi.

Isospora belli is an infrequent cause of diarrhoea in AIDS patients in the USA and Europe but accounts for up to 25% cases of chronic diarrhoea in patients in tropical and subtropical countries. Response to trimethoprim­sulphamethoxazole has been described.

Cyclospora sp. is the most recent protozoan to be associated with diarrhoea in AIDS. It appears to be more common in the developing world and in returning travellers and like Isospora belli appears to be sensitive to trimethoprim-sulphamethoxazole.

Other protozoa including Entamoeba histolytica are frequently identified in stools from HIV-infected homosexual men but appear not to be pathogenic.

Cytomegalovirus colitis occurs in less than 5% of patients with AIDS. Symptoms include bloody diarrhoea, abdominal pain, and fever. Sigmoidoscopy may show diffuse erythema and mucosal ulceration. Diagnosis is histopathological and is made on the basis of characteristic intranuclear “owl's-eye” inclusion bodies or detection of CMV antigen with monoclonal antibodies. Treatment is with ganciclovir or foscarnet.

Adenoviruses have been identified by culture and electron microscopy in HIV-infected homosexual men with diarrhoea. No specific treatment is available.