Through a proof-of-concept trial, we discovered that PRP may offer a potential solution for a specific group of patients experiencing anal incontinence following LAR or ISR. PRP derivatives have already been utilized in clinical settings to address a variety of regenerative needs including urinary incontinence, ocular ulcers, bone diseases, tendon injuries and tissue recovery after surgery [25, 26]. Several studies have underlined PRP as a safe and promising treatment for musculoskeletal maladies since it may contribute to the regeneration of the muscle cells, although its efficacy varies depending on specific indications [27]. A recent meta-analysis of prospective randomized trials has concluded that PRP is safe and effective in treating anal fistula [12]. Due to its regenerative properties, PRP can potentially be a logical treatment option for anal incontinence after rectal cancer surgery although it has yet to be tested in this context. As such, the current study hypothesized that PRP injection could be a useful option for addressing treatment of anal incontinence after LAR of ISR and enhance quality of life.

To homogenize the information and focus on fecal incontinence occurring after low anterior or intersphincteric resection, we used PRP for a highly selective group of patients. Cases with normal manometric findings were not included in the study. Patients with proven loss of rectal compliance or reduction in maximum tolerable volume or with an anatomical defect in the external muscle were also excluded since incontinence was probably not related to the functional deficiency in sphincter functions. Similarly, patients with lower external sphincter volume were not included because of the technical difficulty in accurate injection of the material in the muscles (see Table 3).

The primary focus of this study was to assess the efficacy of PRP injection in improving the Wexner score by a minimum of 2 points. We opted this scoring system and threshold level as previous studies have suggested that the Wexner score is the most suitable measure for assessing the severity of fecal incontinence, and 2 point improvement is deemed clinically significant [23, 24]. Although 35% of the study patients (n = 7) exhibited > 2 point improvement, comparison of pre- and post-injection Wexner scores did not reveal statistical significance. This may be because PRP did not work in some cases as several patients had the same or even worse Wexner scores after injection. Additionally, a smaller group of patients was able to discontinue the use of pads and antidiarrheal medications following PRP injection, while all patients had been using these items at the beginning of the study. The current information can be interpreted from two opposite perspectives. At first glance, one might conclude that PRP injection is not a viable option for incontinent patients due to the lack of significant difference between the pre- and post-injection Wexner scores. However, it is important to consider that a notable 35% of the cases did experience a clinically meaningful improvement in their incontinence scores, with some patients even reporting positive changes in their daily lives. Therefore, we believe that PRP injection has the potential to be helpful and warrants further investigation in future controlled trials.

Objective measures including manometry and EAUS were utilized for the evaluation of PRP injection to assess functional and anatomical changes, respectively. The manometric examinations revealed significant progress in squeezing pressure, indicating external sphincter function improvement following PRP injection. This is a promising outcome effect since it quantitatively demonstrates the functional effectiveness in such cases. These findings are in line with previous studies which have reported an improvement in parenchymal recovery and reduction in fibrotic scar size with PRP injection into the skeletal muscles [25,26,27]. However, our results failed to reveal statistical differences in pre- and post-injection EAUS measures for anatomical changes. This may be attributed to the challenge of identifying and measuring small changes in perianal muscle volumes. Additionally, manometric evaluation did not show a significant improvement in resting pressure. This could be due to the operation technique used on the patients as many underwent an intersphincteric resection that resulted in partial or total removal of internal sphincters. Additionally, even though our goal was to inject PRP directly into both internal and external muscles, some cases did not allow perfect visualization of the structures for injection due to narrower or defective internal muscles. However, we did observe that the improved group had slightly longer internal muscles, although the comparison was borderline insignificant (p = 0.057). Thus, we believe that an internal muscle reserve could be an important criterion for achieving better results after PRP injection. Furthermore, manometry examinations revealed a significant recovery in the first sensation with PRP injection. Although we are not sure of the exact reason for this finding, PRP may influence sensorial behaviors in the anal transitional zone. Further research is necessary to investigate this potential advantage of PRP in incontinent patients. Based on our research, use of PRP injections was found to positively impact certain aspects of QoL including physical functioning, role limitations, emotional well-being and social functioning. Nevertheless, it remains uncertain whether these improvements are attributable to the actual benefits of PRP treatment or simply a placebo effect given that patients are still taking medications and utilizing pads.

Long-term effect of PRP application was analyzed, and Wexner scores were evaluated at least 4 years after PRP application. Since four out of five patients who responded to the questionnaire reported stable Wexner scores, we believe that the improvement gained with PRP application remains secure in the long term in most of the patients who benefit at the beginning.

Current study aims to identify the factors that can predict the patients who would benefit from PRP application. The study found that type 2 diabetes was the sole significant aspect, as all three patients with type 2 diabetes reported a boost in their Wexner scores following PRP injection. Nevertheless, since there was only a limited number of patients with type 2 diabetes, the validity of this finding may be subject to debate.

A significant argument may be made regarding the clinical relevance of the improvement in Wexner scores after PRP injection. Although one-third of the patients declared > 2 points of progress in their Wexner scores, among this group, only one (5%) stopped using pads and three (15%) stopped taking antidiarrheal medications. So, we believe that although an improvement of > 2 points in Wexner scores in 35% of patients is a meaningful finding, the clinical consequence of PRP application in these cases may not be remarkable and has an impact on patients’ daily lives. This is probably a critical subject to be analyzed in further studies.

This study has certain strengths and limitations. The inclusion criteria were very selective, as PRP injection theoretically had the greatest impact on patients with weakened muscle strength. Therefore, patients with a loss of rectal compliance or insufficient neo-rectum volume identified during the manometer evaluation were excluded, while those with weakened perianal muscle strength were included as they were more likely to benefit from PRP injection. Another advantage is that the evaluation measures were multidimensional and included both patient-reported outcomes and several objective measures. Accordingly, the response to treatment was evaluated using QoL and incontinence questionnaires, as well as some objective measures including EAUS and anal manometer, to reveal anatomical and functional changes following PRP injection. The most significant limitation was the lack of a control group since the study was designed as a proof-of-concept trial. Besides, a study without a control group cannot rule out the potential effects of other causes on changes in QoL and improvement in continence over time after surviving cancer.

While the small sample size may be considered acceptable for an early phase or pilot study, it is also important to note that a few participants withdrew before undergoing manometry (n = 4) and EAUS (n = 3) 6 months after PRP application. Therefore, the final analyses for these measures were completed in 17 and 16 cases, respectively. Additionally, there is concern about confusing Wexner scores obtained at 6 months. Most patients remained stable or experienced limited or significant improvement in the severity of their incontinence; however, worse Wexner scores than initial ones were reported in some cases. A recent study on the expectations of community-living incontinent individuals regarding fecal incontinence treatments revealed that the highest priority of incontinent patients was complete elimination of fecal incontinence as well as a decrease in the amount and frequency of leaks [28]. Although the reason(s) for this unexpected outcome in the current study remains unclear, it might be related to higher expectations of the patients receiving PRP injection, and we cannot entirely dismiss the possibility of a true-negative impact of PRP on incontinence severity. Finally, the current study could not measure the effect of neoadjuvant radiation/chemoradiation on sphincter functions, since almost all patients received radiation before the operation. In addition, all patients were asked to continue regular pelvic exercises, and the benefit may be related to this practice.

In conclusion, considering the primary outcome measure, PRP did not improve the Wexner scores in fecal incontinence patients after rectal cancer surgery. However, administering PRP injection to perianal muscles may be advantageous for certain incontinent patients since this treatment can potentially improve their Wexner scores. The benefit in Wexner scores seems to continue in long-term follow-up. Additionally, some patients may no longer need to rely on medications or pads. PRP injection can improve the squeezing pressure and first sensation feeling in manometer examination as well as improve a few QoL measures. Nevertheless, further research is warranted to identify patient subpopulations that are most likely to benefit from PRP injection.