Neural pathway of bellows response during SNM treatment revisited: Conclusive evidence for direct efferent motor
Donald Vaganée1,2, Jeroen Voorham3, Jalesh N Panicker4
1Department of Urology, Antwerp University Hospital, Edegem, Belgium.
Background:
In sacral neuromodulation (SNM) patients, it is thought the bellows response elicited upon sacral spinal nerve stimulation is reflex-mediated. Therefore the mechanism of action of SNM is considered to be at the spinal or supraspinal level. These ideas need to be challenged.
Objective:
To identify the neural pathway of the bellows response upon sacral spinal nerve stimulation.
Design, Setting, And Participants:
Single tertiary center, prospective study (December 2017-June 2019) including 29 patients with overactive bladder refractory to first-line treatment.
Intervention:
Recording of the pelvic floor muscle response (PFMR) using a camcorder and electromyography (EMG) (intravaginal probe and concentric needles) upon increasing stimulation during lead or implantable pulse generator placement.
Outcome Measurements And Statistical Analysis:
The lowest stimulation intensity needed to elicit a visual PFMR and electrical PFMR was determined. Electrical PFMRs were subdivided according to their latency.
Outcome:
the association between visual and electrical PFMRs. Statistical analyses were performed using the weighted kappa coefficient.
Results:
Three different electrical PFMRs could be identified by surface and needle EMG, corresponding with a direct efferent motor response (R1), oligosynaptic (R2), and polysynaptic (R3) afferent reflex response. Only the R1 electrical PFMR was perfectly associated with the visual PFMR (κ = 0.900).
Conclusions:
The visual PFMRs upon sacral spinal nerve stimulation are direct efferent motor responses. A reopening of the discussion on the mechanism of action of SNM is possibly justified.
