Cortico-anorectal, Spino-anorectal, and Cortico-spinal Nerve Conduction and Locus of Neuronal Injury in Patients With Fecal Incontinence

Background & aims: The neuropathophysiology of fecal incontinence (FI) is incompletely understood. We examined the efferent brain-anorectal and spino-anorectal motor-evoked potentials (MEP) to characterize the locus of neuronal injury in patients with FI.

Methods: We performed bilateral transcranial, translumbar, and transsacral magnetic stimulations in 27 patients with FI (19 female) and 31 healthy individuals (controls, 20 female) from 2015 through 2017. MEPs were recorded simultaneously from the rectum and anus using 4 ring electrodes. The difference in MEP latencies between the transcranial (TMS) and translumbar transsacral magnetic stimulations was calculated as cortico-spinal conduction time. MEP data were compared between patients with FI and controls. Patients filled out questionnaires that assessed the severity and effects of FI.

Results: The MEP latencies with TMS were significantly longer in patients with FI than controls at most sites, and on both sides (P < .05). Almost all translumbar and transsacral MEP latencies were significantly prolonged in patients with FI vs controls (P < .01). The cortico-spinal conduction time were similar, on both sides, between patients with FI and controls. Ninety-three percent of patients had 1 or more abnormal translumbar and transsacral latencies, but neuropathy was patchy and variable, and not associated with sex or anal sphincter function or defects.

Conclusions: Patients with FI have significant neuropathy that affects the cortico-anorectal and spino-anorectal efferent pathways. The primary loci are the lumbo-rectal, lumbo-anal, sacro-rectal, and sacro-anal nerves; the cortico-spinal segment appears intact. Peripheral spino-anal and spino-rectal neuropathy might therefore contribute to the pathogenesis of FI.