Faecal incontinence is a common and debilitating condition with multifactorial aetiologies. While pudendal nerve and anal sphincter neuromuscular dysfunction are thought to be important contributors in many instances, currently available diagnostic techniques unable to objectively assess their function. Also, while effective treatment options such as physiotherapy, surgery, and sacral neuromodulation are available for faecal incontinence, there is limited ability for existing diagnostic methods to predict treatment responses. We developed and evaluated a device to detect anorectal high-density electromyography (HD-EMG) of motor-evoked potentials (MEP) via trans-sacral magnetic stimulation (TSMS). We anticipate that improved diagnostic accuracy of neuromuscular dysfunction, and novel biomarkers, will inform and improve treatment decisions.

Patients undergoing pelvic floor investigations were recruited for this study. Anorectal probes with an 8x8 array of 1 cm spaced electrodes were developed for recording HD-EMG of the external anal sphincter. This probe provides spatiotemporal data of the electrical function of the external anal sphincter from both voluntary squeezes and evoked contractions from the TSMS of the pudendal nerve. HD-EMG probes were used to map motor-evoked potential amplitudes and latencies evoked via TSMS delivered with a powerful electromagnet, Magstim Rapid (Dyfed, UK). (Figure 1) In addition to the data from the HD EMG probes, the faecal incontinence severity index, anorectal manometry and endoanal ultrasound data were also collected.

Eleven participants were recruited. Feasibility, safety, and diagnostic workflows were established. The test was well tolerated with median discomfort scores ≤2.5/10, median pain scores ≤1/10, and no adverse events. Novel biomarkers of MEP latency and amplitude were developed.(Figure 2) Both MEP latency and amplitude significantly correlated with faecal incontinence severity index. Worse incontinence correlated with longer MEP latencies (r = 0.58, p <0.001) and lower amplitudes (r = -0.32, p=0.046).

TSMS and HD-EMG of the anorectum generate clinically valid biomarkers of neuromuscular function (latency, and amplitude), that correlate with symptom severity. This is a novel, safe, and well-tolerated diagnostic test.

This high-density EMG probe, in conjunction with trans-sacral magnetic stimulation, presents a novel diagnostic tool for evaluating pudendal nerve and external anal sphincter neuromuscular function. Further evaluation within the IDEAL framework for integration of new technologies into clinical practice are required to translate these novel biomarkers within a clinical decision-making pathway. Future studies should focus on assessing for correlations between the neuromuscular biomarkers and longer-term treatment outcomes. We present early evaluation of a novel diagnostic method. If, as we expect, the novel biomarkers are predictive of outcomes to treatment, this will mean a significant improvement in the care of this common and debilitating condition.