Tenesmus is an intense, painful but fruitless desire to defaecate. It may be continuous or recurrent. The rectum feels full, but when the patient tries to pass a stool, nothing appears, or a little blood and mucus is passed.
Tenesmus is caused by a space-occupying lesion in the lumen or wall of the rectum that mimics the presence of faeces (e.g. polyp, carcinoma, thrombosed pile), or by miscellaneous causes such as proctitis and irritable bowel syndrome.