Neurophysiological modification of pelvic floor parameters during sacral nerve neuromodulation
Original article by ELENA ANDRETTA (1) - EDOARDO OSTARDO (2) - CRISTINA ZULIANI (3)
LAURA DE BIAGGI (4) - TIZIANA DE SANTO (4)
(1) Department of Urology - General Hospital Dolo (Venice)
(2) Department of Urology - City Hospital S.ta Maria degli Angeli Pordenone
(3) Department of Neurology - General Hospital Mirano (Venice)
(4) Medtronic Italia
Key words: Sacral nerve stimulation, Pelvic floor, IPG, Perineal innervation.
INTRODUCTION
Sacral neuromodulation (SNM) works on the neural
reflexes that influence the bladder, rectum and pelvic floor.
Since the initial experience of the nineteen eighties SNM
has been widely used to treat both bladder and rectal dysfunction
but the exact mechanism of action is still unknown.
The aim of this study was to investigate the functional modifications
of peripheral perineal innervation using SNM.
MATERIALS AND METHODS
The study involved 27 patients (3 males, 24 females)
affected by urinary incontinence (44%), urinary retention
(30%), obstructed defecation (18%), fecal incontinence
(4%), and chronic pelvic pain (4%). The average treatment
time - using Interstim implantable pulse generator (IPG) -
was 56 months (range 19-88) and all patients experienced
full remission of symptoms with the electrical parameters
individually programmed. The following tests were performed:
1) Electromyography (EMG) of the external anal
sphincter (EAS); 2) EMG of the urethral sphincter (US)
at rest, in voluntary contraction and in reflex contraction;
3) Somatosensory evoked potentials (SEPs); 4) Pudendal
nerve terminal motor latency (PNTML). The tests were performed
with IPG on and off and data were statistically analyzed
using the Student's t-test.
RESULTS
We observed the following significant changes: EMG 1)
A rise in amplitude of motor unit potentials (MUPs) during
maximal contraction in the US with IPG on - average 31.5
± 24.4 uV compared to IPG off average 25.5 ± 25.8 uV -
(p = 0.058). 2) Duration of MUPs at resting was decreased
with IGP switched on and this decrease was greater for US
- average 4.2 ± 0.9 msec compared to IPG off average 4.6
± 1.1 msec (p = 0.010) - as well as for EAS - average 3.4.
± 0.9 ms compared to IPG off average 4.2 ± 1.2 ms (p =
0.049). (Figs. 1, 2, 3) 
PNTML. After the IPG was turned on,
examination of PNTML revealed a decrease in latencies on
both sides. The data collected were: average 1.8 ± 0.36 msec
compared to IPG off average 1.9 ± 0.37 msec (p = 0.036)
on stimulated side and average 1.85 ± 0.6 msec compared to
IPG off average 2.1 ± 0.9 msec (p = 0.024) on the unstimulated
side (Fig. 4).
The remaining examinations and parameters were
unchanged.
DISCUSSION
Some Authors 1, 2, 3 suggested the use of electrodiagnostic
techniques in order to better or to reprogram SNM but
nobody has reported improve studies about the effects of
SNM on perineal responses. We have observed that SNM produces significant changes
in EMG and in PNTML. With regard to EMG, SNM has
increased the amplitude of activation pattern in US and has
decreased the MUPs duration at rest in both sphincters.
These
results suggest a greater recruitment of pelvic muscular fibers
and a better synchronization of fibers firing, moreover lasting
in time. The decrease of latencies in PNTML, observed on
both sides, probably means that SNM stimulates motor conduction
velocity of pudendal nerves and suppresses integration
between peripheral innervation and spinal cord.
CONCLUSIONS
SNM produces significant modifications in function of
peripheral perineal innervation. We observed an increase of
amplitude of voluntary contraction in SU-EMG, a decrease
of duration of MUP at rest in sphincters and a decrease of
latencies of PNTML on both sides.
- Benson JT. Sacral nerve stimulation results may be improved by electrodiagnostic techniques. Int Urogynecol J 2000; 11: 352-7.
- McLennan MT. The role of electrodiagnostic techniques in the reprogramming of patients with a delayed suboptimal response to sacral nerve stimulation. Int Urogynecol J 2003; 14: 98-103.
- Malaguti S, Spinelli M, Giardiello G, Lazzeri M, Van Den HomberghU. Neurophysiological evidence may predict the outcome of sacral neuromodulation. J Urol 2003; 170: 2323-2326.
Correspondence to:
Dr. ELENA ANDRETTA
E-mail: elenaandretta@libero.it