Preoperative chemoradiation for rectal cancer causes prolonged pudendal nerve terminal motor latency

PURPOSE: A worsened anorectal function after chemoradiation for high-risk rectal cancer is often attributed to radiation damage of the anorectum and pelvic floor. Its impact on pudendal nerve function is unclear. This prospective study evaluated the short-term effect of preoperative combined chemoradiation on anorectal physiologic and pudendal nerve function. METHODS: Sixty-six patients (39 men, 27 women) with localized resectable (T3, T4, or N1) rectal cancer were included in the study. All patients received 45 Gy (1.8 Gy/day in 25 fractions) over five weeks, plus 5-fluorouracil ( 350 mg/m(2)/day) and leucovorin (20 mg/m(2)/day) concurrently on days 1 to 5 and 29 to 33. Patients who had rectal cancer with a distal margin within 6 cm of the anal verge had the anus included in the field of radiotherapy ( Group A, n = 26). Patients who had rectal cancer with a distal margin 6 to 12 cm from the anal verge had shielding of the anus during radiotherapy ( Group B, n = 40). The Wexner continence score, anorectal manometry and pudendal nerve terminal motor latency were assessed at baseline and four weeks after completion of chemoradiation. RESULTS: The median Wexner score deteriorated significantly ( P < 0.0001) from 0 to 2.5 for both Groups A ( range, 0 - 8) and B ( range, 0 - 14). The maximum resting anal pressures were unchanged after chemoradiation. The maximum squeeze anal pressures were reduced ( mean = 166.5 - 157.5 mmHg) after chemoradiation. This change was similar in both Groups A and B. Eighteen patients ( Group A = 7, Group B = 11) developed prolonged pudendal nerve terminal motor latency after chemoradiation. These 18 patients similarly had a worsened median Wexner continence score ( range, 0 - 3) and maximum squeeze anal pressures ( mean = 165.5 - 144 mmHg). The results obtained were independent of tumor response to chemoradiation. CONCLUSIONS: Preoperative chemoradiation for rectal cancer carries a significant risk of pudendal neuropathy, which might contribute to the incidence of fecal incontinence after restorative proctectomy for rectal cancer.