Unilateral vs bilateral sacral neuromodulation in pigs with formalin-induced detrusor hyperactivity

To investigate the efficacy of unilateral vs bilateral sacral neuromodulation (SNM) under standard experimental conditions by stimulating the dorsal sacral roots in pigs with formalin-induced detrusor hyperactivity. After lumbosacral laminectomy in eight alpha-chloralose-anaesthetized Gottinger mini-pigs, the dorsal roots of the nerve S3 were inserted into separate compartments of a size-modified Brindley electrode. Detrusor hyperactivity was induced by intravesical instillation of a 0.25% formalin solution. Stimulation of the separated dorsal roots was performed on the unilateral right, respectively, the unilateral left side, as well as bilaterally and with stimulation off-phases in a randomized pattern. A biphasic rectangular signal (impulse 200 mu s, 20 Hz, 2.0 V) was used for SNM. The bladder pressure values were registered on a urodynamic unit and evaluated as contractions and amplitudes per minute. During unilateral stimulation, the mean (sem) number of contractions was reduced significantly from 4.73 (0.66) to 2.73 (0.62). The amplitude was also reduced significantly from 12.86 (1.23) to 8.32 (0.66). By contrast, bilateral stimulation lowered the mean (sem) number of overactive detrusor contractions to 1.08 (1.02) and the amplitude to 3.08 (2.42), which are highly significant reductions. In this porcine model, bilateral neurostimulation was a more effective method of SNM than unilateral stimulation. We assume that this is due to the additive effect of stimulating both sides, as well as the greater chance of stimulating the relevant dorsal roots of the sacral nerve fibres. By contrast, unilateral neuromodulation may be only partially effective by not being capable of influencing the entire bladder, or possibly by allowing new formation of neuronal pathophysiological pathways.