The effect of sacral nerve modulation on cerebral evoked potential latency in fecal incontinence and constipation

Influence of sacral nerve modulation (SNM) on cerebral somatosensory evoked potentials (SEP) was determined in patients with incontinence and constipation.

Selection of patients with incontinence and constipation for SNM could be improved.

The latency (ms) of SEP induced by pudendal nerve stimulation was compared before (T0) and at 1 month during peripheral nerve evaluation (PNE) of SNM at frequencies of 21 Hz (T1) and 40 Hz (T2). The results were correlated with clinical outcome at 6 months.

In 16 of 23 incontinent patients with clinical "success" from SNM (Wexner incontinence score ≤7), there was a significant difference between P40 latency at T0 and T2 (38.81 vs. 37.49 ms, P = 0.049). In the 7 with "failure," there was no change between T0 and T2. In 12 of 19 constipated patients with "success" (Wexner constipation score ≤15), there was no difference between T0 and T2 P40 latency (39.28 vs. 38.25 ms, P = 0.374). In the 7 with "failure," there was a significant fall in P40 latency (41.20 vs. 39.30 ms, P = 0.047) but not to the normal range. The T0 P40 latency in incontinent patients having "success" was significantly higher than in the normal range (P = 0.044). In constipated patients it was significantly higher than in the normal range in both those with "success" (P = 0.001) and "failure" (P = 0.022).

Measurement of P40 latency of SEP at baseline and at 1 month of SNM at a frequency of 40 Hz may help to predict the outcome of SNM and thus influence the decision for permanent implantation for patients with incontinence and constipation.