Sacral neuromodulation for low urinary tract dysfunction: overview and mechanisms of action

Objectives

Sacral neuromodulation (SNM) is widely used since the 1990's for overactive bladder (OAB) and non-obstructive urinary retention (NOUR) with good clinical results. Though, its mechanisms of action are not fully elucidated.

Materials and methods

This narrative review intends to explore the various hypotheses of mechanisms of action in SNM, and to propose a theoretical model of action based on the current literature.

Results

SNM may modulate afferent signaling primarily through sub-sensory activation of pelvic floor muscles, which in turn may generate afferent input transmitted via the spinal cord to supraspinal structures, rather than through direct afferent neural stimulation. SNM may restore the balance between the sympathetic nervous system (SNS) and parasympathetic nervous system (PSNS) by decreasing activity in the anterior cingulate cortex and increasing activity in the median prefrontal cortex. SNM may also modulate the activity of the limbic system (cingulate cortex, insula), that is related to emotions and is frequently dysregulated in Fowler's syndrome – a specific NOUR entity, and patients with OAB. In NOUR, SNM may restore the periaqueductal gray activity through a diminution of excessive inhibitory afferent messages, particularly through modification of the activity of the median prefrontal cortex. Finally, sacral neuromodulation (SNM) may influence neural plasticity at the peripheral, spinal, and/or supraspinal levels; however, the underlying mechanisms and specific neurophysiological changes remain incompletely understood.

Conclusion

While our understanding of the mechanisms of action of SNM is still evolving, emerging data point toward a multifaceted process involving modulation of peripheral afferent input, spinal processing, and supraspinal structures - including those involved in sensorimotor integration, emotional regulation, and autonomic balance.