What is the exact working mechanism of botulinum toxin A and sacral neuromodulation in the treatment of overactive bladder / detrusor overactivity? ICI-RS 2017

Aims: Botulinum toxin A (BTX-A) and sacral neuromodulation (SNS) are well established treatments for overactive bladder (OAB) and appear as standard of care in refractory cases in many international urological guidelines related to the subject. Despite long term use over decades their ‘exact’ working mechanisms are not entirely clear. At the ICI-RS meeting in Bristol in 2016 a think tank was convened to address the question.

Methods: The think tank conducted a literature review and an expert consensus meeting focussing on current established mechanisms and what could be learned from clinical experience and objective urodynamic data.

Results: Clinical and urodynamic results with BTX-A suggests effects on both filling and voiding parts of the micturition cycle. The salient data in this regard is presented as well as additional studies related to the urothelium and evidence for more central effects. Urodynamics have shown consistently increases in cystometric, bladder compliance and reductions in detrusor pressures during filling, however post void residuals also increase in a dose dependent fashion. During SNM activation of somatic afferent nerves inhibits bladder sensory pathways and reflex bladder hyperactivity. Evidence in the cat model suggests the inhibition of bladder activity occurs primarily in the CNS by inhibition of the ascending or descending pathways of the spinobulbospinal micturition reflex. Urodynamics have suggested improvement in filling phase such as increases in cystometric capacity and reduction in detrusor pressures during filling with little observed effects on voiding parameters.

Conclusions: The working mechanism of BTX-A and SNS is complex. The exact mechanisms are still unknown, although considerable progress has been made in our understanding. Further research proposals are suggested to help further elucidate these mechanisms.