Introduction

Sacral nerve stimulation (SNS) is a U.S. Food and Drug Administration-approved treatment that has grown in popularity over the years for its effectiveness and relatively long durability at treating refractory lower urinary tract as well as bowel symptoms, particularly overactive bladder (OAB) symptoms, nonobstructive urine retention and fecal incontinence.^{1, 2} Lead migration is a known complication of SNS with a reported rate of 10%–35%.^3–5 Herein, we present a case of device malfunction through lead migration due to twisting of the lead wires requiring surgical revision.

Case Report

The subject is a 70-year-old woman with a history of total hysterectomy, chronic lower back and radiating leg pain, and multiple back surgeries, who presented to us 8 years ago with mixed urinary incontinence. The patient had transobturator tape sling for mixed urinary incontinence, and her stress urinary incontinence had improved but she still had residual urge urinary incontinence that failed medical therapy. Accordingly, InterStim^® (Medtronic, Minneapolis, Minnesota) placement was planned after discussing treatment options with the patient. The procedure was performed in October 2014. The lead was placed on the right S3 sacral foramen and the battery on the left lower back. The patient experienced improvement of her urinary symptoms. During the course of her followup, the patient developed chronic lower back and leg pain, possibly attributable to myoskeletal causes, indicating magnetic resonance imaging (MRI) of the spine. Given the MRI incompatibility of the old implanted InterStim device, she had her device removed in August 2017. The device was reimplanted in November 2017 with successful results (Fig. 1). Recently, she encountered multiple falls and developed recurrence of her storage lower urinary tract symptoms. Interrogation of the implantable pulse generator (IPG) and lead revealed high impedance, which suggested lead breakage. Followup pelvic x-ray showed abnormal twisting and full migration of the lead from the sacral bone (Fig. 2). The patient was counseled about the findings, and since she previously experienced improvement of lower urinary tract symptoms she was counseled on InterStim revision and replacement with the new MRI-compatible IPG and lead. During the procedure, we found the lead completely broken off the IPG, fully migrated off the sacrum and with multiple bizarre twists. Another interesting intraoperative finding was that the IPG was found to be freely floating in the pocket, with the pocket seeming too capacious (Fig. 3). The old implant was removed, the IPG pocket was refashioned and a new InterStim device was placed without difficulties with return to baseline urinary function.

Discussion

Figure 1. Initial pelvic x-ray after device reimplantation showing the device in correct position. A, posteroanterior view. B, lateral view.

Figure 2. Followup pelvic x-ray showing lead migration. A, posteroanterior view. B, lateral view.

This is an unusual case of InterStim lead migration where the lead became dislodged from the sacrum and twisted multiple times within the IPG pocket, which ultimately led to complete detachment of the IPG from the lead. While rare, this most likely occurred due to significant capacious pocket being left behind, allowing for the multiple twisting to occur. This is supported by the fact that we found the IPG to be freely floating inside the pocket and the fact that the IPG will not be allowed to flip multiple times creating those twists without enough room to do so. Guzman-Negron et al in 2020 described 2 similar cases.⁶ One patient had recurrent OAB symptoms after full InterStim implant and was found to have lead migration with twisting. The second patient underwent a full InterStim implant with initial improvement of symptoms which recurred 6 months later without any history of trauma, and the twisted lead wire was again replaced with no difficulty. Siegel et al in 2000 reported their experience with 219 patients in the original MDT-103 study where they identified complications in 181 participants, most of which were secondary to lead migration (11.8%) and lead and/or IPG-related pain (17.4%), with approximately 10.5% having their implant explanted for lack of efficacy after initial successful lead stimulation.³ Additionally, van Kerrebroeck et al in 2007 followed 163 SNS patients for 5 years and noted that 19.9% and 42.1% of patients required surgical intervention due to complications at year 1 and 5, respectively.⁷ However, they attributed this high complication rate to the fact that their study population included complicated cases that had undergone surgery during the procedure learning curve and with relatively old surgical techniques.⁷ Moreover, White et al in 2009 concluded that after a mean followup of approximately 3 years, 30.3% of their SNS patients experienced complications, with lead migration, infection and IPG-related pain occurring in 5.9%, 3.5% and 2.7% of the patients, respectively, while confirming a history of trauma, chronic pain and duration of followup to be frequently implicated.⁸ Lead migration rates appear to vary in the literature, potentially explained by varying implanter experiences, differing clinical practices and different definitions of migration. Our case brings an interesting point that falls/trauma may be another factor responsible for leaving the patient susceptible to future device dysfunction due to breakage or lead damage. In those situations, it may be prudent to perform device interrogation and system check. In addition, we found a pelvic x-ray to be very helpful in identifying the lead position. To prevent future occurrences, we recommend creating a suitable sized pocket for the IPG. Too tight a pocket space can lead to erosion of the implant and chronic pain. Too spacious a pocket, on the other hand, can risk fluid collection/infection as well as similar complications of lead twisting and IPG malposition as in this case.

Figure 3. Intraoperative pictures of the lead and IPG.

Conclusion

InterStim is an established treatment modality for refractory OAB. Lead migration is a known complication of the procedure. Recurrence of patient urinary and/or fecal symptoms raises the suspicion of lead migration. InterStim device interrogation and pelvic x-ray can help establish the diagnosis. Proper patient counseling to avoid lead/IPG trauma and physical shock as well as sticking to the proper technique can help minimize this complication.