Sigmoidoscopy and rectal biopsy

Sigmoidoscopy is a procedure done to identify the cause of persistent diarrhoea or of abnormal bleeding from the lower bowel. It is commonly carried out when the results of stool cultures have not been able to identify the cause of diarrhoea.

A rigid sigmoidoscope is the usual tool for rectal biopsy. It can only be passed approximately 15cm into the bowel and looks mainly at the rectum. Occasionally, a flexible sigmoidoscope (or colonoscope) is used; this is a flexible tube containing optical fibres.

A laxative is given prior to the procedure to ensure that the views of the bowel are not obscured; a bowel wash-out is usually not required. Small pieces of abnormal-appearing tissue (biopsies) are taken from the lining of the bowel to be analysed.

Possible lesions, inflammation, and ulceration of the rectum or colon can be seen and a possible cause for bleeding may be identified by this procedure. The biopsy specimens will help diagnose the cause of diarrhoea. Possible causes of diarrhoea could be cytomegalovirus (CMV), colitis, cryptosporidiosis, mycobacterium avium intracellulare (MAI) infection, or microsporidiosis.