Clinical and Urodynamic Predictors for Sacral Neuromodulation Outcomes in Overactive Bladder

Overactive bladder syndrome (OAB) is a prevalent disorder that affects about 10% of the adult population and \> 40% of elderly. It is defined by the presence of urgency, with or without urge incontinence, in the absence of infection or other pathology. In 1997 through 1999, sacral nerve stimulation SNS (InterStim, Medtronic Inc., Minneapolis, Minnesota) was approved by the U.S. Food and Drug Administration (FDA) for treating urge urinary incontinence, urinary urgency, and frequency. Despite the large numbers of SNS performed, the only objective clinical evaluation of OAB is urodynamic detrusor instability (UDI) with some evidence suggesting a correlation with outcomes after sacral neuromodulation. Interestingly, the mechanism of action of SNS is not fully understood. Theories include direct activation of efferent fibers to the striated urethral sphincter causing reflex relaxation of the detrusor or potential activation of afferent fibers selectively which can lead to inhibition at spinal and supraspinal levels. Somatic sacral afferent inflow activation at sacral level affects the storage and emptying reflexes in the bladder and central nervous system, explaining the beneficial effects of neuromodulation on both storage and emptying functions of the bladder. Malaguti and his colleagues detected somatosensory evoked potentials during sacral neuromodulation, revealing that sacral neuromodulation works by both sacral afferent activity and somatosensory cortex activation. As sacral neuromodulation is clinically proven for both storage and emptying bladder dysfunctions, it is difficult to isolate its action to either sacral afferent or efferent circuits in the micturition reflex pathway. In our study, we are going to study sacral neuromodulation outcome predictors from the clinical and urodynamic perspectives in order to help identifying the right candidates for sacral neuromodulation procedure.