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/m²/day) and leucovorin (20 mg/m²/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. Poster presentation at the meeting of The American Society of Colon and Rectal Surgeons, Philadelphia, Pennsylvania, April 30 to May 5, 2005.