The relationships between the results of contemporary tests of anorectal structure and sensorimotor function and the severity of fecal incontinence

Background: Diagnostic investigations for fecal incontinence (FI) assess the structure and sensorimotor function of the anorectum. Investigations include anorectal manometry, anorectal sensory testing, pudendal nerve terminal motor latencies (PNTML), and endoanal sonography. The severity of FI and results of investigations are often discordant and the rate of symptom resolution following treatment remains <40%. High-resolution anorectal manometry (HRAM) and three-dimensional endoanal ultrasound (3D-US) have been introduced during the last decade. This study aims to assess the strength of relationships between contemporary investigation results and FI severity. Methods: Adults presenting for investigation of FI were assessed using the St Mark’s FI severity score (SMIS), HRAM, anorectal sensory testing, PNTML, and 3D-US. Key Results: 246 patients were included. There were significant relationships between the SMIS and HRAM (resting pressure r_s = −0.23, 95% CI = (−0.34, −0.11), P <.001; squeeze pressure (r_s= −0.26, 95% CI = (−0.37, −0.14), P <.001) and 3D-US (anterior EAS length r_s = −0.22, 95% CI = (−0.34, −0.09), P =.001). The relationships between SMIS and HRAM had a greater effect size in those with urge-predominant symptoms (resting pressure: r_s = −0.40, 95% CI = (−0.57, −0.20), P <.001, squeeze pressure: r_s = −0.34, 95% CI = (−0.52, −0.12), P =.003). Overall, the variance in SMIS accounted for by anorectal investigations was 8.6% (R² = 0.098, adjusted R² = 0.086, P <.001). Conclusions and Inferences: Anorectal investigations are not strong predictors of FI severity. These findings may reflect the multifactorial, heterogeneous pathophysiology of FI, the limitations of the SMIS and anorectal investigations, and contributing factors extrinsic to the anorectum.