The Problematic Sacral Neuromodulation


Used in this review

Definition

Used in the literature

Reportable events

Suboptimal therapeutic responses and adverse events as defined below

Complications, treatment failure

1. Suboptimal therapeutic responses

Lack of efficacy

Inadequate clinical benefit or reduced response after the definitive implantation of a device. The improvement experienced during PNE is not reproduced and the patient has little or no clinically meaningful effect without a period of satisfactory outcome

Less satisfactory results, unsatisfactory results

Loss of efficacy

Reduction or cessation of therapeutic benefit after a period of satisfactory results. The patient had symptom improvement during PNE that was reproduced after device implantation, but the effect was lost either gradually or suddenly during the treatment period

Faded clinical response, less satisfactory results, results

2. Adverse events

Any new-onset symptom or medical problem that occurred during SNS and affected the patient unfavorably and was deemed to be related to the treatment (both device- and therapy-related)

Included terminology: pain, infection, urinary retention, change of sexual function, electric shock sensation, diarrhea

InterStim technical terminologies

Stimulator

Medtronic model 3023, 3058, Twin

IPG, pacemaker, InterStim, InterStimII

Permanent lead/Tined quadripolar lead

Medtronic model 3080, 3093, nontined or tined quadripolar lead

Electrode, quadripolar lead

Temporary lead

Medtronic model 3057, model 041830, nontined helical/nonhelical monopolar lead

Temporary wire, nonhelical wire, helical wire

Temporary stimulator

Medtronic model 3625
 
Device

Implanted stimulator and permanent lead

System

Displacement

The implanted lead has moved either completely or partially from the position

Dislodgement, dislocation, migration

Breakage

Obvious transection or kink of the lead

Bent lead

Surgical interventions

Replacement of permanent lead

Implantation of a new permanent lead

Lead revision

Repositioning of permanent lead

Implantation of the same or a new permanent lead in a different foramen

Re-siting of lead

Re-siting of stimulator

Relocation of the stimulator to a different site

Relocation of IPG/stimulator

Explantation

Removal of the permanent lead or stimulator or both

Removal

Other clinical management

Reprogramming

Change of stimulating poles and parameters (amplitude only, frequency and pulse width remain the same)

Reprogramming

Alternative programming

Change of stimulating pole combination and parameters (including change of pulse width and/or frequency)

Increase/decrease pulse width, frequency, or both

Termination

Termination of stimulation without device explantation

Treatment stop


Abbreviations: PNE peripheral or percutaneous nerve evaluation, IPG implantable pulse generator





Problems Associated with SNS



Suboptimal Outcome


Suboptimal outcome can be divided into two main categories:



  • Lack of efficacy: when the improvement experienced during the period of PNE is not reproduced and the patient has little or no clinically meaningful benefit after implantation


  • Loss of efficacy: when the improvement of symptoms ­during PNE is reproduced after SNS device implantation but the effect is lost either gradually or suddenly.

Lack or loss of efficacy is one of the most common problems after implantation, and its incidence is estimated to be as high as 12 % when assessing available data concerning the use of SNS for fecal incontinence [4]. One of the potential reasons for early failure is suboptimal location of the permanent device (quadripolar foramen electrode, usually a tined lead). This is often prematurely interpreted as a problem inherent in non-staged techniques during PNE. In a ­non-staged procedure, a thin, monopolar electrode is used during PNE and a permanent electrode and stimulator are subsequently implanted as a separate procedure. This may result in the permanent electrode not being placed in a ­position identical to that which resulted in an initially good response during PNE. This problem may be avoided with a staged process in which a permanent electrode is used for PNE; if this is clinically beneficial, a second stage procedure will merely involve connecting the lead that is already in place for conversion to an implant, which would then be attached to an added stimulator. This latter technique is more costly and usually is limited to the placement of one electrode during PNE. However, no study has yet specifically addressed comparative clinical outcomes between these two approaches.

Another possible cause for lack of efficacy is instability of the permanent electrode in the postoperative period and stabilization by fibrosis. As a consequence, it can be difficult to find an optimal stimulation setting without uncomfortable side effects.

Eventual loss of efficacy is less well understood and likely due to multiple causes often acting together. Mechanical factors relating to the device, such as electrode migration, a broken fiber within the electrode, a loose connection, or surrounding fibrosis with a loss of conduction, are speculated to play a larger role in lack of effectiveness with time. Nerve injury or damage during prolonged stimulation may contribute to alterations in longer-term efficacy, but our current knowledge of variations in neurophysiological and neurochemical mechanisms involved in SNS is ­limited. Furthermore, any progressive neurological disease may account for an initially positive therapeutic effect and potential worsening of a preexisting condition over time which may be beyond the therapeutic benefit of SNS implantation.


Pain


Pain can be caused by the mechanical presence of the device or may be an adverse effect of stimulation. The estimated incidence is 13.0 % [4, 5]. Pain is most commonly reported at the site of the implanted stimulator [3]. The presence of the impulse generator itself can result in skin erosion, hematoma, cellulitis, local allergic reaction, seroma, or wound dehiscence. If the patient loses a significant amount of weight and a substantial amount of subcutaneous tissue, the device can protrude. Pain in other sites, including the perineum, leg, or foot, also has been reported and in most cases seems to be an adverse effect of stimulation.


Infection


The reported incidence of infection is 3.9 % [6, 7]; however, a large multicenter study of SNS in fecal incontinence reported a rate of 10.8 %, with most infections occurring within 3 weeks of device implantation [8]. Staphylococcus aureus is the most frequent causative bacterium, which may be detected on tined leads [9].


Adverse Stimulation Effect


During SNS in fecal incontinence, adverse functional effects have been reported, including the need for deactivation during defecation and urination, respectively [10, 11]. Sleep disturbance may necessitate switching off stimulation at or during periods of increased sexual drive [12]. In a single report, one patient complained of a sensation of a minor electric shock when passing through an ambient electric or magnetic field (such as a store’s antitheft security system). The effect of SNS on pregnancy also is poorly understood or not well documented, for example, in one report a patient who had stimulation until 9 weeks of gestation prematurely delivered an infant with Down’s syndrome [13].


Broader Perspectives on Suboptimal Outcome and Adverse Events Associated with SNS


Treatment with SNS for functional bowel disorders followed on the success of the treatment in urinary incontinence, about which there have been substantially more reports with longer urologic follow-up. In these analyses, the incidence of suboptimal clinical benefit and complications was not uncommon: studies have shown that between 53 and 67 % of patients experienced at least one device- or therapy-related adverse event [1417] and between 30 and 54 % required surgical revision. The most common indications for surgical revision were pain around the stimulator and infection. The rate of device explantation because of either failure or adverse events has been reported at between 6 and 50 % [11].


Management of Suboptimal Outcome and Adverse Events: A General Approach


Apr 18, 2016 | Posted by in Reconstructive surgery | Comments Off on The Problematic Sacral Neuromodulation

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