Detrusor underactivity (DU) is defined as low detrusor pressure or short detrusor contraction in combination with a low urine flow rate resulting in prolonged bladder emptying and/or a failure to achieve complete bladder emptying within a normal time span; a high postvoid residual may be present [1]. Treatment of DU is a real challenge: pharmacologic treatment is usually ineffective, whilst surgery is not indicated. Neuromodulation techniques have been used in patients with LUTS; in particular, percutaneous tibial nerve stimulation (PTNS) has shown to be promising in treating detrusor overactivity and has been proposed also for the treatment of non-obstructive urinary retention; however, there are no conclusive study on the efficacy of PTNS on DU [2]. In addition, there are no factors that can help to foresee patients’ response to PTNS or that might be predictive of success, defined as improvements in voiding, storage and quality of life. The aim of this study was to investigate which parameters are able to predict the success of PTNS in non-neurologic patients with DU.

This was a prospective non controlled single center study in non-neurologic patients who underwent PTNS for DU in 2021. Exclusion criteria were neurologic diseases, diabetes and concomitant urinary tract infections. All patients had a complete urodynamic to confirm the diagnosis of DU and were evaluated with IPSS (International Prostatic Symptoms Score) and IPSS QoL (International Prostatic Symptoms Score Quality of Life) questionnaire, bladder diaries and uroflowmetry before and after completing the PTNS cycle (12 sessions). Patients’ satisfaction to treatment was evaluated with Patient Global Impression of Improvement (PGI-I) scale (from 1= “very much better” to 7= “very much worse”) and the scores 1-2 were used to define success. Basing on PGI-I, patients were divided in responders and non-responders. Data regarding age, sex, IPSS, bladder diaries, intensity of stimulation used and presence of flexion of the big toe during PTNS were collected, compared between the two groups (responders vs. non-responders) and analyzed. Fisher’s exact test was used to examine the significance of the association between the variables and treatment outcome, and p-value was considered significant for when < 0.05).

A total of 17 patient (age range 26-76 years; mean age 45,6 years; median age 36 years; M=11, F=6) with a diagnosis of DU were included in this study. Eleven patients (64,7%) reported significant improvements of their urinary symptoms and were considered responders (PGI-I: 1 or 2), whilst six patients (35,3%) did not report any improvement and were considered non responders (Figure 1). Of all parameters evaluated, age, sex, intensity of stimulation used, changes in bladder diaries were comparable and did not show any significant difference among responders and non-responders. Before treatment, IPSS values were on average lower among the responders, while IPSS QoL were similar; after treatment, both IPSS and IPSS QoL showed a significant improvement in the responders [IPSS: from mean 19.7 to 12.18 (↓38.17%); QoL: from mean 4.54 to 2.91 (↓35.9%)], while a similar trend was not observed in the non-responders [IPSS: from mean 26.5 to 22.5 (↓12.1%); QoL: from mean 4.66 to 4.66 (↓0%)]. Flexion of the distal phalanx of the big toe was found to be significantly more frequent among the responders: in fact, it was present in 10 out of 11 responders (90,9%) whilst it was reported for only 1 out of 6 non responders (16,6%) (P-value 0.005) (Figure 2).

At present, there are no conclusive studies on the efficacy of PTNS on treatment on DU and no predictive factors of successful outcome for PTNS in detrusor underactivity have been found. According to our data, more than 60% of the patients undergoing PTNS for DU reported improvement in their LUTS, confirmed by better IPSS and IPSS QoL values after treatment. In addition, we found that age, sex, IPSS, and variables from bladder diaries are not predictive of PTNS success. Interestingly, we found that the intensity of stimulation used every session showed no relation with the rate of success. According to our data, only the presence of the flexion of the distal phalanx of the big toe was significantly associated with a successful outcome at the end of the treatment and could be considered a predictive factor for success in patients treated with PTNS for DU. This finding was not reported or noted in previous studies and further research are needed for validating our data and evaluating if flexion of the big toe may be critical in predicting the success of PTNS also in overactive or/and neurologic patients. Moreover, it suggests that re-positioning the needle whenever the flexion of the big toe cannot be elicited could improve the rate of response and therefore the success of PTNS.

In conclusion, the flexion of the big toe during PTNS is the only factor that can predict success of PTNS treatment, defined as patients’ subjective improvement. This highlights the importance of provoking the big toe’s flexion during the stimulation, suggesting that needle re-positioning might be needed whenever the flexion does not happen. Further studies are needed to confirm this finding and to further validate the use of PTNS in patients with DU.

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Gaziev G, Topazio L, Iacovelli V, Asimakopoulos A, Di Santo A, De Nunzio C, Finazzi-Agrò E. Percutaneous Tibial Nerve Stimulation (PTNS) efficacy in the treatment of lower urinary tract dysfunctions: a systematic review. BMC Urol. 2013 Nov 25;13:61. doi: 10.1186/1471-2490-13-61. PMID: 24274173; PMCID: PMC4222591.