Sacral neuromodulation is a medical technique that involves the application of electrical stimulation at the S3 nerve root. Generally, electrical stimulation therapy seeks to artificially galvanize efferent neurons or neuromuscular junctions via low-energy electrical pulses, causing involuntary muscle contractions that, over time, can strengthen and improve voluntary muscle function. Sacral neuromodulation in particular evolved from the general field of transcutaneous electric nerve stimulation (TENS), but was modified to include subcutaneous implantation of an electric stimulating device at the base of the spinal cord. It is typically considered for patients that require long-term rehabilitation.
Sacral neuromodulation is practiced therapeutically with the aim of either activating or inhibiting the contraction of the external sphincter and pelvic floor muscle. Electrical stimulation occurs at a frequency of 2.1-130Hz[1] and is used to treat organ or muscular malfunction in the genital region. Common ailments which may be alleviated by sacral neuromodulation include excessive frequency of urination, urinary retention, obstructive defecation, sexual dysfunction, and pelvic pain,[2] as well as fecal incontinence.[3] Given that implantation involves surgery, it is generally considered as an option only for patients that have seen little improvement with non-invasive treatment. However, therapeutic success remains moderately high, ranging from 61 to 90 percent.[4]
Prior to reversible placement of an implantable pulse generator (IPG), a testing phase of 2-8 weeks must be completed to ensure that the patient is likely to benefit from sacral neuromodulation. Local anesthesia is first administered to alleviate discomfort. Three small incisions are made in the upper buttock region, then a temporary lead is inserted and connected to an external pulse generator. If the patient experiences a significant improvement of symptoms, an IPG is placed in the upper buttock region as a more permanent solution.[5] The sacral neuromodulation implantation procedure is relatively safe and has not been known to result in death. However, common negative outcomes of the procedure include infection (up to 10 percent of cases),[6] pain at the implantation site (14 percent), and necessary lead revision or replacement (16 percent).[7] Given these complications, reoperation rates have been reported as high as 39 percent.[8]
Given the pain and recovery time associated with surgical implantation of an IPG, some patients opt for percutaneous tibial nerve stimulation (PTNS), which is a low-risk, non-surgical treatment. PTNS requires 12-weekly, 30-minute treatments, in which a needle electrode is placed at the tibial nerve and sends electric impulses to the sacral nerve plexus. The therapy is relatively painless and patients typically describe a “tingling” sensation.[9] However, studies have found improved clinical outcome with sacral neuromodulation as opposed to PTNS,[10] and permanent implantation allows for increased ease of treatment in patients that require long-term therapy. Furthermore, the FDA is currently reviewing a proposal for an IPG that is 80 percent smaller and rechargeable, which may significantly reduce the severity and frequency of surgery.[11],[12] Therefore, physicians will likely have to carefully consider the needs of the patient when presenting either therapy as a suitable option.
References
[1] SUMMARY OF SAFETY AND EFFECTIVENESS DATA (SSED). Axonics Sacral Neuromodulation (SNM) System for Urinary Control – P180046 2019. https://www.fda.gov/medical-devices/recently-approved-devices/axonics-sacral-neuromodulation-snm-system-urinary-control-p180046.
[2] Sucar-Romero S, Escobar-del Barco L, Rodríguez-Colorado S, Gorbea-Chávez V. Estimulación del nervio tibial posterior como tratamiento de la disfunción del piso pélvico. Revisión de la bibliografia [Posterior tibial nerve stimulation for pelvic floor dysfunction. Review]. Ginecol Obstet Mex. 2014;82(8):535-546.
[3] Gupta P, Ehlert MJ, Sirls LT, Peters KM. Percutaneous tibial nerve stimulation and sacral neuromodulation: an update. Curr Urol Rep. 2015;16(2):4. doi:10.1007/s11934-014-0479-1.
[4] Tutolo M, Ammirati E, Van der Aa F. What Is New in Neuromodulation for Overactive Bladder?. Eur Urol Focus. 2018;4(1):49-53. doi:10.1016/j.euf.2018.04.019.
[5] Sacral Neuromodulation: A Guide for Women. The Pelvic Floor Society UK. 2013.
[6] Lee, C., Pizarro-Berdichevsky, J., Clifton, M.M. et al. Sacral Neuromodulation Implant Infection: Risk Factors and Prevention. Curr Urol Rep. 2017; doi:10.1007/s11934-017-0663-1.
[7] Sacral Neuromodulation (Bladder Pacemaker). Melbourne Bladder Clinic. 2016.
[8] Gevelinger M.M., Sanderson D.J., Jaworski E., Doyle P.J.
Evaluation of Sacral Nerve Stimulation Device Revision and Explantation in a Single Center, Multidisciplinary Study. Neuromodulation, 2019; doi:10.1053/j.scrs.2017.07.006.
[9] Percutaneous Tibial Nerve Stimulation – PTNS – Overactive Bladder. Urology Austin 2020. https://urologyaustin.com/urology-specialties/percutaneous-tibial-nerve-stimulation-ptns/.
[10] Simillis C, Lal N, Qiu S, et al. Sacral nerve stimulation versus percutaneous tibial nerve stimulation for faecal incontinence: a systematic review and meta-analysis. Int J Colorectal Dis. 2018;33(5):645-648. doi:10.1007/s00384-018-2976-z.
[11] Blok B, Kerrebroeck PV, Wachter SD, Ruffion A, Aa FVD, Jairam R, et al. Three month clinical results with a rechargeable sacral neuromodulation system for the treatment of overactive bladder. Neurourology and Urodynamics 2018; doi:10.1002/nau.23465.
[12] Coolen RL, Groen J, Blok B. Electrical stimulation in the treatment of bladder dysfunction: technology update. Med Devices (Auckl). 2019; 12:337–45.