Sacral neuromodulation (SNM) is a two-stage surgical procedure for refractory bladder dysfunctions and faecal incontinence. Appropriate screening for success during the test period (Stage I) to determine a good candidate for a full implant (Stage II) is crucial since the high financial burden for the social security. Ideally screening of subjective and objective success is performed by the evaluation of standardized patient reported outcome measures (PROMS) and an accurate analysis of bladder and/or bowel diaries, so as standard of care prescribes. We aimed to carry out a quality control on our own tertiary centre screening and decision strategy by answering the following research questions: 1) Is the current decision strategy on our SNM patient population applied conform the standard of care? 2) What is the current prevalence of false positive cases at short term follow-up, i.e. 1 month after Stage II? and 3) Can we reduce the number of false positive cases by applying the standard of care?

A single tertiary centre prospective study was held between February 2018 and October 2019.  Fifty-three patients planned for a two-stage tined lead procedure, from both the Urology (UD) (n= 36) and Colorectal surgery department (CRD) (n=17) were enrolled. According to the current practice, the decision to proceed from Stage I to Stage II (i.e. positive advice) was made at the control visit during the test period. The evaluation was accomplished based on a quick, rather intuitive screening for changes in bladder and bowel diary parameters and on the anamnesis of patient satisfaction. As a quality control on the physician’s advice for implant, a mathematical re-analysis of bladder and bowel diaries was performed after the control visit. An improvement of at least 50% in one or more of the bothersome voiding and/or bowel diary parameters was considered as objective success (ObS). Subjective success (SS) was defined as a score of ≥ 5/7 on the validated Patient Global Impression of Change (PGIC) questionnaire, administered at the end of the test period (PGIC1) and at 1 month after Stage II (PGIC2). Correct advice according to standard of care was fulfilled if both ObS and SS were present. False positive cases were defined as patients reporting a PGIC2 score < 5/7 (no change to somewhat better, but hardly any difference), in spite of having SS during the test phase and being implanted. Patients with missing PCIG1 scores and missing diaries were excluded from analyses (n=12).  Descriptive statistics using SPSS version 25.0 were performed.

Forty-two patients were included for analysis, median age (IQR) 52 years (46-64), 76% female. Indications were OAB wet (n=10), OAB dry (n=2) & bladder pain syndrome (BPS) (n=2), non-obstructive urinary retention (n=6), Fowler syndrome (n=5), faecal incontinence (n=7) and combined incontinence (n=10). The total conversion rate was 81% (34/42), with a 81% (26/32) and 80% (8/10) implantation rate for UD and CRD respectively. 1) A positive advice for implantation had a positive predictive value (PPV) of 94% (32/34) to predict the presence of both ObS and SS and a negative predictive value (NPV) of 75% (6/8). This implicates that 9% of the cases (4/42) got incorrect advice for implantation conform the criteria of standard of care. 2) Twenty-eight patients from the 34 implanted cases completed the PGIC2 questionnaire. Continued SS (PGIC2 ≥ 5/7) was reported in 89% (24/27), implicating a prevalence of false positive cases of 11% (3/27). In one case subjective success at 6 months follow-up was restored after reprogramming.  3) Two on 4 implanted cases with absence of SS at 1 month follow-up, did not show concomitant ObS and SS during the test phase, the other 2 on 4 did.

1) Ninety-one percent (38/42) of the advices under the current decision practice were given conform the criteria of standard of care. However, 2 patients being good candidates for a full implant were incorrectly refused from Stage II, whereas 2 patients who did not show both ObS and SS during the test phase got incorrectly a positive advice for implant. 2 + 3) The prevalence of false positives is rather low. However, this number could have been reduced if both the objective and subjective changes would have been assessed by thorough mathematical diary analysis and the use of a standardized questionnaire. Nevertheless, a small percentage (2/4) of cases with loss of SS at 1 month follow-up couldn’t have been avoided if standard of care would have been applied. The sample size of false positive cases was too small to conduct a multivariate analysis in search of predictive factors for this loss of SS, but a possible placebo effect should be kept in mind.

Ninety-one percent of the advices for implantation in our tertiary centre met the criteria of standard of care. Moreover, the prevalence of false positives at one month follow-up showed to be low. Thorough analysis of both objective and subjective success and the requisite of meeting both criteria can reduce the number of false positive cases at 1 month, but cannot completely avoid them. In the future more research is needed to define factors, others than inaccurate screening, that can predict loss of subjective success.