Editing Functional: Neuromodulation (section)

=== Technique ===

* '''<span style="color:#ff0000">Sacral nerve stimulation (SNS) by the InterStim procedure is performed in 2 stages:'''
** '''<span style="color:#ff0000">Stage I: clinical trial of a temporary or permanent lead for external stimulation'''
** '''<span style="color:#ff0000">Stage II: implantation of a subcutaneous implantable pulse generator (IPG)'''

==== Stage I ====

* '''During the initial introduction of sacral neuromodulation therapy, patients undergo a percutaneous nerve evaluation by the placement of a unilateral percutaneous lead in the S3 foramen'''
** Whereas some physicians still prefer to perform the first stage by a percutaneous nerve evaluation approach, many have adopted a permanent tined lead placement
* Insert figure
* '''Procedure'''
** '''The location of the S3 foramen is approximated by measuring 9 cm cephalad to the drop-off of the sacrum and 1-2 cm lateral to the midline on either side'''.
** '''<span style="color:#ff0000">The nerve is tested for the appropriate S3 motor response:'''
*** '''Test stimulation is repeated on each electrode, and the responses are observed.'''
*** '''Sacral nerve responses'''

{| class="wikitable"
|'''Nerve root'''
|'''Motor'''
|'''Sensory'''
|-
|'''S2'''
|'''Plantarflexion of the entire foot with lateral rotation''' and clamp movement of the anal sphincter
|'''Leg and thigh'''
|-
|'''<span style="color:#ff0000">S3'''
|
* '''<span style="color:#ff0000">Plantar flexion of the great toe[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1476095/&#x20;say&#x20;plantar&#x20;flexion §] AND'''
* '''<span style="color:#ff0000">Bellows reflex (anal wink. contraction of the perineal area, which represents contraction of the levator muscles)'''
|Parasthesias or sensation of pulling of '''<span style="color:#ff0000">rectum, scrotum, or vagina'''
|-
|'''S4'''
|'''Bellows reflex only'''
|Sensation of pulling in the '''rectum only'''
|}

*'''<span style="color:#ff0000">An S3 response should be noted on ≥2 of the electrodes'''
** '''A sensory response is not needed to confirm proper placement if the correct S3 motor response is observed, although this is debatable.'''
*** '''Although controversial, proper localization of the device may be improved if one can localize the stimulation at the time of lead positioning to sensation of the vagina-rectum juncture in females and perineoscrotal area in males'''
**'''When a motor response is absent despite correct placement:'''
**# '''Ensure that the patient has muscle twitches and is not under neuromuscular blockade.'''
**# '''After confirming lack of neurmuscular blockage, raising the conscious level of the patient during the procedure and detecting the correct sensory response will confirm proper localization'''
*** '''A clinical response may still be obtained during the screening trial period despite the absence of the motor response'''
** '''Follow-up'''
*** '''Changes in LUTS and postvoid residuals (PVRs) are recorded in a detailed bladder diary'''
**** '''If improvement is minimal or absent, revision or bilateral percutaneous lead placement may be attempted.'''
**** '''If > 50% improvement in symptoms of urgency/frequency or urgency urinary incontinence is attained, a permanent IPG is implanted'''
*** '''The length of the trial with the external pulse generator may vary slightly from patient to patient, by the indication, and by the surgeon’s practice preference.'''
**** '''In patients with urgency/frequency and urgency urinary incontinence, a 1-2-week trial is generally adequate.'''
**** '''For retention, a longer trial of 3-4 weeks or more may be necessary before a desired clinical response is obtained.'''

==== Stage II ====

* '''Entails placement of the IPG'''