Functional: Neuromodulation: Difference between revisions

* '''Pudendal Nerve'''

** Because the bladder afferent reflex works through sacral interneurons that then activate storage through pudendal nerve efferent pathways directed toward the urethral sphincter, the pudendal nerve is a logical target for developing neuromodulation therapies

** Neurophysiologic studies reveal that SNS works for bladder storage disorders by a similar inhibition of the micturition reflex as a result of electrical stimulation of sensory afferent fibers, in particular by depolarization of Aα and Aγ somatomotor fibers that affect the pelvic floor and external sphincter and thus inhibit detrusor activity. Because many of the sensory afferent nerve fibers contained in the sacral spinal nerves originate in the pudendal nerve, the pudendal nerve afferents are important targets for neuromodulating the inhibitory reflex on the micturition reflex

** '''Direct pudendal nerve neuromodulation stimulates more pudendal afferents than SNS provides and may do so without the side effects of off-target stimulation of leg and buttock muscles.'''

* '''Dorsal Genital Nerve''' (dorsal nerve of the penis in males, clitoral nerve in females)

** The terminal and most superficial branches of the pudendal nerve

** Found at the level of the symphysis pubis.

** Afferent nerves that carry sensory information from the glans of the penis or clitoris.

** Proximally, the dorsal genital nerves form a component of the pudendal nerve and then the sacral spinal roots.

** Contributes to the pudendal-pelvic nerve reflex that has been proposed as a mechanism of bladder inhibition.

*** Whereas squeezing the glans penis or manipulation of the clitoris is clinically known to help suppress bladder contractions as observed in behaviors of voiding avoidance, direct electrical stimulation of these organs does not produce a significant effect on the micturition reflex as measured by urodynamics during the storage phase. However, direct dorsal genital nerve electrical stimulation in experimental and clinical studies appears promising in producing an inhibition of the micturition reflex

* '''Posterior Tibial Nerve'''

** '''A mixed sensory and motor nerve'''

** '''Contains fibers originating from spinal roots L4 through S3 that modulate the somatic and autonomic nerves to the pelvic floor muscles, bladder, and urinary sphincter.'''

** Clinical trials of PTNS have been performed in detrusor overactive conditions with and without pelvic pain and urinary retention. Although clinical trials have produced variable results, PTNS is minimally invasive, demonstrates efficacy, and is easily applicable and well tolerated in all the LUT conditions studied.

** '''One of the major limitations of this therapy is the need for continued and repeated sessions'''

* '''Transcutaneous Electrical Stimulation'''

** Other methods of electrical stimulation have been used that seem to occupy a place midway between anal, vaginal, or perineal stimulation and sacral root stimulation

* '''Emerging Role for OnabotulinumtoxinA vs. Sacral Neuromodulation in Overactive Bladder'''

** The increasing use of OBTX in the therapy for OAB has yielded questions to how to decide whether to use OBTX or sacral neuromodulation in patients with refractory OAB.

** At present, patients with emptying disorders or those at risk for urinary retention who do not want to catheterize would not be ideal candidates for OBTX. Furthermore, these patients need to be aware of the re-treatment intervals approximately every 6 months and this may aid in decision making. On the contrary, if someone has neurogenic conditions, is not willing to undergo an implant (permanent), or may need future MRIs, sacral neuromodulation becomes a less attractive option.

* '''Complications and Troubleshooting of Sacral Neuromodulation'''

** '''Categorized as percutaneous test stimulation vs post-implant complications'''

*** '''Test stimulation'''

***# '''Lead migration (most common,''' 12%)

***# '''Technical problems'''

***# '''Pain'''

*** '''Post-implantation'''

**** '''Pain''' (15% at 12 months)

**** '''Pocket (IPG) Discomfort'''

***** '''Classified as pocket vs. output related'''

****** '''Pocket-related causes of discomfort include infection, pocket location (waistline), pocket dimension (too tight, too loose), seroma, and erosion'''

****** '''Output-related causes include sensitivity to unipolar stimulation (if this mode is used) or current leak.'''

***** '''See CW11 Figure 81-10 for Troubleshooting Algorithm for Implantable Pulse Generator Site Discomfort'''

***** '''Diagnosis and Evaluation'''

****** '''Turn off the device and ask the patient if the discomfort is still present to differentiate pocket-related from output-related causes'''

******* '''If the discomfort disappears, device output is probably causing discomfort.'''

******** '''Output-related'''

********* '''If the stimulation program is unipolar, switch to bipolar and see whether that eliminates discomfort.'''

********** Some patients are sensitive to the unipolar mode of stimulation, because the positive pole is the neurostimulator.

********* '''Another possibility is leakage of fluid into the connector.'''

********** This somehow creates a short circuit whereby the current from the device follows this fluid pathway out to the patient’s tissue.

********** Most patients report this as a burning sensation. Even though current is following this fluid out to the patient’s tissue, some of the current also may be getting to the electrodes as well, so some patients feel both burning in the pocket and stimulation in the perineum.

********** Reprogramming around this can be tried by using different electrode combinations.

*********** If reprogramming is unsuccessful, the patient is asked if the “burning” sensation is tolerable (it will not harm the patient’s tissues); if it is not tolerable, a revision may be necessary to dry out the connection sites

******** '''Pocket-related'''

********* '''If the discomfort persists, the cause is not related to the device output.'''

********* '''In the absence of clinical signs of infection, pocket-related causes such as pocket size, seroma, and erosion must be considered.'''

**** '''Surgical revision'''

***** '''Performed in 33% of cases to resolve an adverse event.'''

****** This included relocation of the neurostimulator because of pain at the subcutaneous pocket site and revision of the lead for suspected migration.

****** At the time of this study, the generator was implanted in the lower abdomen. This profile of complications has changed dramatically with use of the InterStim II generator and posterior (gluteal) pocket location.

***** '''Explant of the system was performed in 10% for lack of efficacy'''

**** '''Infection'''

***** '''Management: explantation of the whole system.'''

****** To date, no preoperative or perioperative antibiotic regimen has been decided to be best and should otherwise be left to surgeon discretion.

******* Antibiotic consideration should otherwise be targeted toward skin site pathogens and methicillin-resistant Staphylococcus aureus.

**** '''Decreased or absent response after a successful interval'''

***** '''See CW11 Figure 81-8 in Campbell's Urology for Diagnostic Algorithm and Troubleshooting for Recurrent Symptoms'''

***** '''When the patient presents with recurrent symptoms, evaluation of the stimulation perception is necessary. The possibilities are that the patient perceives:'''

****** '''The stimulation in a wrong location compared with baseline'''

****** '''No stimulation'''

****** '''Intermittent stimulation'''

****** Documentation of the exact location and amplitudes of the best stimulation parameters should be done early after successful implantation, to set as a baseline so when changes occur, the baseline can be noted.

***** '''Impedance measurement is used to check the integrity of the system when a patient presents with a sudden or gradual disappearance of stimulation'''

****** '''Impedance describes the resistance to the flow of electrons through a circuit.'''

******* The electrical circuit in this context starts at the neurostimulator’s circuitry and goes through the connectors to the extension wires, through the extension connector to the lead wires, through the lead’s electrodes to the patient’s tissue, and back either through another electrode and up the same path to the circuitry (bipolar) or to the neurostimulator case and into the circuitry (unipolar).

******* Most measurements of impedance fall within the 400- to 1500-ohm range.

******** '''If there is too much resistance, no current will flow (open).'''

******** '''If there is too little resistance, excessive current flow results in diminished battery longevity (short).'''

****** '''Open circuits'''

******* '''Can be caused by a fractured lead or extension wires and loose connections'''

******** If the circuit is broken somehow, electrons cannot flow

******* '''Impedance measurements are high (>4000 ohms)'''

******** '''Unipolar measurements are most useful for identifying open circuits''' because they take one lead wire measurement at a time, immediately identifying which connection or wire has the problem.

******* '''Patients generally feel no stimulation if an open circuit is present'''

****** '''Short circuits'''

******* '''Can be caused by body fluid intrusion into the connectors or crushed wires that are touching each other'''

******** Electrons always will follow the path of least resistance

******* '''Impedance measurements are low (<50 ohms) (short = low)'''

******** '''Bipolar measurements are most useful for identifying short circuits'''

******* '''Patients may or may not feel stimulation, or stimulation may not be present in the correct area''' (i.e., the generator site) '''or may vary in strength''' (i.e., a surging sensation).

***** The intraoperative algorithm for management of impedance problems includes initial testing of impedances; most physicians bypass intraoperative electrodiagnostics and just change the lead to avoid any continued problems postoperatively.

***** '''Wrong Location'''

****** '''If the patient reports that the stimulation location or pattern has changed, it is best to go back to each unipolar setting and map where the patient feels the stimulation.'''

******* The device is set to 0−, case+ and the patient is asked where she or he feels the sensation; next it is set to 1−, case+ and the patient again is asked about the sensation; next it is set to 2−, case+ and finally to 3−, case+.

******* '''If these combinations do not confirm the target area, the next step is to start programming bipolar combinations.'''

******* When those are exhausted, sometimes increasing the pulse width widens the stimulation area

******* If the programming possibilities are exhausted, revision for lead repositioning or relocation to the other side may be necessary.

***** '''No Stimulation'''

****** The obvious is checked first: the device parameters must be set high enough, an inadvertent on-off is checked (set magnet switch off to avoid inadvertent magnet activations), and whether the IPG is nearing the end of its life is checked.

****** Next, impedance readings are performed, paying close attention to unipolar impedances. These impedances measure one lead wire with the case, so it is easy to isolate a problem. Using unipolar impedances, it is possible to tell which lead wires are still intact and which ones are not, as mentioned previously. Programming of the electrodes is then continued with acceptable impedance measurements.

****** Bipolar measurements are checked to rule out short circuits as well (very low impedance measurements). If programming around the malfunctioning lead does not restore the stimulation, the patient will often need to undergo revision.

***** '''Intermittent Stimulation'''

****** Again, inadvertent on-off is checked.

****** Intermittent stimulation can be caused by either a loose connection or positional sensitivity. If a loose connection is suspected, palpating the connection site and re-creating the intermittency is a good clue as to where the problem lies.

****** Taking impedances while the patient reports the stimulation intermittently determines whether the problem is positional (acceptable impedances are still present) or mechanical (when the patient feels stimulation go off, the impedances are high).

****** With positional sensitivity, the lead position shifts when a patient moves in a certain direction (e.g., the patient reports that the stimulation goes away on standing). The lead position may have moved farther from the nerve during standing, and the amplitude may just need to be increased.

****** Intermittent stimulation represents a challenging dilemma to troubleshoot.