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
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 [14–17] 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
One must establish whether an adverse event is a result of treatment and identify any mechanically correctable factors. A general algorithm for troubleshooting management is depicted in Fig. 35.1