A deep dive in sacral neuromodulation to improve its efficacy and understanding of its action
Authors:   , Tilborghs Sam 
Published: July 2024

Sacral neuromodulation (SNM) is an effective treatment for patients with voiding dysfunctions, such as overactive bladder (OAB) and nonobstructive urinary retention (NOUR), that are resistant or intolerant to conservative treatments. These conditions significantly impact quality of life and healthcare costs. This thesis reviews studies on SNM and OAB, focusing on patient selection, lead placement, testing techniques, and safety and efficacy to enhance successful SNM therapy outcomes. SNM has proven to be safe and effective for treating OAB in the short-, medium-, and long-term without limiting other treatment options. No major irreversible complications were noted. Key factors for successful SNM therapy include patient selection, lead placement, and testing techniques. While no consensus on predictive factors for patient selection exists, the first-stage tined lead procedure has shown more reliable testing results and better patient selection for SNM compared to percutaneous nerve evaluation (PNE). The test stimulation phase remains the most crucial prognostic factor for long-term success. Chapter 2 investigates if a “supervised” three-week test phase increases the success rate and relates the need for reprogramming during the test phase to the one-year outcome for implanted patients. Our data showed that weekly follow-ups and reprogramming during a three-week test phase increased the number of patients who responded successfully and proceeded to implantation and chronic SNM treatment with proven durable success. Thus, a supervised three-week test phase is recommended. Chapter 3 assesses the neurophysiological basis behind troubleshooting and reprogramming by analyzing motor and sensory responses to lead stimulation. Monopolar configurations provided more efficient therapy delivery than bipolar configurations. Swapping polarity or changing the cathode position led to different sensory and motor responses, offering potential reprogramming options. These findings serve as a guiding tool during reprogramming and a basis for further research on clinical outcomes. Chapters 4 and 5 explore the use of pelvic floor muscle (PFM) electromyography (EMG) during lead placement and programming as a predictor of a successful SNM test phase. Intraoperative PFM EMG under general anesthesia aids accurate lead targeting. A correlation between therapy efficacy and PFM motor response during programming was found, linking lead placement to SNM outcomes. Responders generally exhibited lower motor thresholds (MT), lower MT/sensory thresholds ratios, higher compound muscle action potentials (CMAPs), and higher continuous PFM activation at subsensory stimulation levels. Chapter 6 examines Burst stimulation, a new SNM paradigm, showing it induced higher bladder and urethral pressure increases than conventional SNM, suggesting a higher degree of autonomic nervous system stimulation. Individual parameters such as frequency and amplitude may be important for SNM efficacy, warranting further research. Chapter 7 discusses the main findings in the context of current knowledge. Chapter 8 provides prospects for SNM in a rapidly evolving patient population.