RE: PUDENDAL NERVE LATENCY TIME IN NORMAL WOMEN VIA INTRAVAGINAL STIMULATION
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GERALDO A. CAVALCANTI, GILBERTO M. MANZANO, LYDIA M. GIULIANO, JOAO A. NOBREGA, MIGUEL SROUGI, HOMERO BRUSCHINI

Division of Urology, University of Sao Paulo School of Medicine (USP), Sao Paulo, Brazil

Int Braz J Urol, 32: 697-704, 2006

To the Editor:

     We have to congratulate Cavalcanti et al. for their very nice study adding information on pudendal pathologies. They concluded that the vaginal approach represents an alternative for pudendal nerve distal motor latency time, with similar results to those achieved through the transrectal approach. Normative values obtained might serve as a comparative basis for subsequent physiopathological studies.
     We have for long time used the 2 approaches (vaginal and rectal) and find sometimes bizarre results. We recall that for measuring pudendal nerve motor time conduction a special device was developed at the St Mark’s London Hospital. It consists of a bipolar stimulating electrode fixed on a gloved index finger. A pair of surface recording electrodes is placed 3 cm proximally on the base of the finger. Using a rectal pathway the stimulating electrode is placed near the ischial spine. The recording electrode is at the level of the anal sphincter. Geraldo and al. describe a transvaginal stimulation. Pudendal nerve motor latency time obtained by transrectal or transvaginal stimulation has to be viewed with some uncertainty and doubts because we must have in mind the imprecision of the stimulation point, which is at the level of the ischial spine.
     An entrapment at this site cannot be detected and distortion of the stimulating potential by the different layers of tissues to go through can explain normal results even in presence of a neuropathy (Cavalcanti et al.). For the last 6 months, we have been use an insulated regional analgesia needle with electro-neuro-stimulation port (100 or 120 mm) placed above the ischial spine (by a transmuscular perineal route parallel to the ischiorectal fossa) to stimulate the pudendal nerve. The recording is made with a circular bipolar electrode placed in the anal sphincter with some advantages: the stimulations are made above the ischial spine permitting a detection of an entrapment even at this site, it localize with accuracy the site of entrapment (sacrospinous ligament, falciformis process, pudendal tunnel), there is less or no distortion of the potential, it can be used in women and men, it can be used as an intraoperative monitoring, it inform the surgeon at the time of the decompression on the ongoing of the procedure or the necessity of completing it, therefore, improving the surgical procedures.

Dr. Eric de Bisschop
Clinique de Montchoisi
Lausanne, Switzerland
E-mail: rajeshree@free.fr

Dr. Jean Pierre Spinosa
Department of Gynecology, Hôpital de Morges
Morges, Switzerland
E-mail: spinosa@deckpoint.ch

REPLY BY THE AUTHORS

     We are grateful for the interest shown in our study and especially thank you for information on potentials improvements in the technique used by Dr. Eric de Bisschop and Dr. Jean Pierre Spinosa.
     They shared their experience in obtaining the pudendal nerve terminal motor latency (PNTML) for both approaches (vaginal and rectal). We agree that imprecision of the stimulation point and the interposition of different layers of tissues between the pudendal nerve and the stimulus electrodes represent technical and biological factors that may interfere in the M-wave recordings, even reaching the supramaximum stimulus. However, the latency value must not be altered by these factors.
     They also described an interesting and novel technique to obtain the PNTML by utilization of needle electrode for pudendal nerve stimulation instead of St. Mark’s electrode. Other authors also designed an intra-rectal incurvated metallic rod stimulator with similar arguments, as an alternative method to assess the PNTML (1). A needle stimulator could obtain more quality recordings because the direct stimuli of the nerve can be reached and specific stimulation areas can be localized with accuracy. But the St. Mark’s electrode used in the study has the distance between the stimuli and recording sites known in a region of difficult access for measuring. This would become the method more standardized and appropriate for pelvic floor, besides probably causing less discomfort than the transmuscular perineal route. These alternative methods for PNTML assessment might be useful in routine practice, mainly for intraoperative monitoring. Nevertheless it should be tested in further studies.

Reference
1. Lefaucheur JP, Yiou R, Thomas C: Pudendal nerve terminal motor latency: age effects and technical considerations. Clin Neurophysiol. 2001; 112: 472-6.