Study of the rectal electric activity of the uninhibited rectal detrusor (overactive rectum): A new concept of pathogenesis

Background/Objective: One of the causes of fecal incontinence is uninhibited rectal detrusor syndrome (URDS). Patients with this condition either perceived the first rectal sensation after the onset of involuntary rectal contraction or not at all. We investigated the hypothesis that the abnormal rectal contractility in URDS may be caused by deranged rectal electric activity. Methods: Twenty-five patients with URD (114 women and 11 men; age, 44.7 +/- 10.3 years) and 10 healthy volunteers (6 women and 4 men; age, 42.8 +/- 8.7 years) were studied. URDS was diagnosed by rectometry and provocative test. A transcutaneous EMG was performed with one electrode placed lateral to each sacroiliac joint and the third one midway between the greater trochanter and the ischial tuberosity. Two 20-minute recording sessions were performed for each subject. Results: Slow waves (SWs) with regular rhythm and similar parameters (frequency, amplitude, conduction velocity) from the 3 electrodes were recorded from the healthy volunteers. They showed a significant increase in the parameters on saline filling of the rectum. The SWs of patients with URDS exhibited a ``dysrhythmic{''} pattern with irregular parameters, which were different in the 3 electrodes and inconsistent during recording. They showed areas of tachyrhythmia, bradyrhythmia, and arrhythmia. On provoking rectal overactivity, the SWs showed an increased dysrhythmic activity. Conclusions: The patients with URD exhibited a ``dysrhythmic{''} electric pattern with areas of variable electric activity. The tachyrhythmic areas seem to initiate the urgency and fecal incontinence of URDS. It is suggested that a disordered rectosigmoid pacemaker causes the dysrhythmic waves.