Pathophysiology of late anorectal dysfunction following external beam radiotherapy for prostate cancer

Patients treated with external beam radiotherapy (EBRT) may suffer from long-term anorectal adverse effects. The purpose of the present study was to assess long-term functional and structural anorectal changes in patients previously treated with EBRT for prostate cancer and to suggest the mechanism behind the development of the adverse effects.

Our previously proposed RT-induced anorectal dysfunction (RT-ARD) score, developed with the intention to survey anorectal dysfunction was used to identify patients with and without anorectal symptoms. Among 309 patients surveyed with the questionnaire, we chose 23 patients with the highest RT-ARD score and 19 patients with the lowest RT-ARD score. They were investigated by multimodal rectal sensory stimulation, standard anal physiological tests. Changes of the rectal mucosa were assessed by flexible sigmoidoscopy and graded by the Vienna Rectoscopy Score (VRS).

The mean follow-up time was 3.8 (range, 2.8; 8.6) years in patients with high RT-ARD and 3.8 (range, 2.6; 5.9) in patients with low RT-ARD. Endoscopic evaluation revealed higher VRS scores in patients with high RT-ARD compared to patients with low RT-ARD (p = 0.002). Patients with high RT-ARD had increased rectal sensory response to distension manifested both as volume (p = 0.006) and cross-sectional area (p = 0.04), and they had reduced maximum anal resting pressure assessed by anal manometri (p = 0.02).

Long-term anorectal symptoms correlate to changes in anorectal biomechanical properties and rectal mucosal injury. Our data suggests that RT-induced long-term anorectal dysfunction is multifactorial caused by injury of the rectal mucosa and the internal anal sphincter combined with increased rectal sensitivity and reduced rectal functional capacity.