The urodynamic study (UDS) is critical for a correct diagnosis and management of neurogenic lower urinary tract dysfunctions (N-LUTD) in patients with spinal cord injuries (SCI): more of 80% of them will experience some kind of N-LUTD which undermine the safe, effective and controlled storage and voiding of urine, may lead to infections and upper urinary tract (UUT) deterioration and have a negative impact on the patients' quality of life [1].
In particular, during the cystometric phase it is possible to evaluate the detrusor overactivity leak point pressure (DOLPP), defined as the lowest detrusor pressure rise with detrusor overactivity at which urine leakage first occurs in the absence of a voluntary detrusor contraction or increased abdominal pressure [2].
The role of DOLPP in the neurogenic population is still controversial for the lack of data and the lack of standardization of its measurement: often mistaken for D-LPP, there are no reliable cut-offs, and a multi-database search did not reveal any specific SCI-based study on neurogenic DOLPP. Moreover, it is not clear if there other urodynamic parameters that may predict the risk of UUT deterioration in this population. 
The primary aim of this study was to investigate the relation between urodynamic (UD) profiles and the onset of vescico-ureteral reflux (VUR) and to determine which urodynamic variable best correlated to VUR, considered a risk-factor for UUT deterioration, in adult SCI patients. Secondary aim was to establish a reliable neurogenic DOLPP cut-off value of safety for UUT.

The study was a retrospective comparative single-centre study based on the review of UDS of adult neurological patients. The UDS have been performed in the years 2010 – 2021 in a referral centre for functional Urology, accordingly to the ICS reports on Good Urodynamic Practices (GUP) [3]. 
SCI patients with a complete filling cystometry, at least 1 cystography or renal ultrasound and a follow-up >1 year were included and data regarding age, history, pharmacological treatment, physical examination, kind of micturition (spontaneous, CIC, CV), UD reports and follow-up were collected and examined. Basing on the presence of VUR at cystography or hydronephrosis at ultrasound, patients were divided into 2 groups (Group A = no VUR; Group B: VUR). Characteristics of our cohorts are reported in Table 1. 
UD parameters such as maximum Cystometric capacity (CCmax), maximum detrusor pressure during filling cystometry (Pdetmax), bladder filling at first detrusor contraction (BF-DC) and N-DOLPP were collected.
Data were entered into Microsoft Excel (Microsoft, Redmond, WA, USA) and compared between the two groups, and the relations between UD variables and VUR were analized. Chi square test was used to compare categorical variable. Quantitative data were compared by Student’s T test for unpaired data. ROC curves were used to evaluate Sensibility (SE) and Specificity (SP) for each NDO-LPP cut and to individuate the optimal NDO-LPP cut-off. P-values <0.05 were considered statistically significant.

A total of 64 patients were included in this study: 53 (82.8%) in Group A (no VUR) and 11 (17.2%) in Group B (VUR).
The two groups were overall homogeneous for characteristics, site of lesions and sex distribution.
Table 2 shows the comparison of the UD variables between the 2 groups: CCmax mean values were significantly lower in group B compared to group A (243.5 ml vs. 447.5 ml, p<0,0001) and so were BF-DC value (146.8 vs. 279.8 ml, p=0,001). Pdetmax and NDO-LPP had instead an opposite trend: they both were significantly higher in group B than in group A. In particular, Pdetmax mean values were 77 cmH2O in group B and 39 cmH2O in group A (p=0,0003), whilst NDO-LPP was 41 cmH2O in group A and 61 cmH2O group B (p=0,025). 
From the ROC curve analysis, the most accurate NDO-LPP cut-off value in term of prediction of VUR was 40 cmH2O: this cut-off allowed to correctly classify 62.5% of patients and showed a sensibility of 72.7% and a specificity of 60.4%.

According to our data, VUR was associated to lower bladder capacity, precocious DO (lower bladder filling at first DC), higher mean N-DOLPP and higher Pdetmax during detrusor overactivity at filling cystometry. These findings are consistent with the existing literature that report that high detrusor pressures, DO and low bladder compliance are linked to an increased risk of UUT damage. 
Considering a cut-off value of 40cmH2O, the incidence of VUR was 28% for NDO-LPP >40 cmH2O, whist it dropped to 9% for lower NDO-LPP. Comparing the NDO-LPP classes (< 40 cmH2O and > 40 cmH2O), the odds ratio for VUR was 4.06 (CI95% 0.97-17.10, p=0.056), therefore NDO-LPP > 40 cmH2O can be considered a risk-factor for developing VUR in neurological SCI patients. No patient with a NDO-LPP <20 cmH2O showed VUR.

Our study confirms the importance of UDS for SCI patients for evaluating the personal risk of UUT damage and establishing an effective treatment. In particular, we found that low bladder capacity, detrusor overactivity at low filling and with high pressure and NDO-LPP > 40 cmH2O are significantly related to the presence of VUR and therefore the ideal treatment should aim to improve bladder capacity and compliance and reduce detrusor overactivity. We also proposed the NDO-LPP 40 cmH2O cut-off as predictor of VUR, the caveat being that it is only a screening tool and it must be paired with other UD variables to better identify patients at high risk of UUT deterioration and optimize their management.

Blok, B. et al. EAU Guidelines on Neuro-Urology EAU Guidelines. Edn. presented at the EAU Annual Congress Amsterdam 2022. (EAU Guidelines Office, Arnhem, The Netherlands. http://uroweb.org/guidelines/compilations-of-all-guidelines/, 2022).
Tarcan, T., Demirkesen, O., Plata, M. & Castro-diaz, D. ICS Teaching Module?: Detrusor Leak Point Pressures in Patients With Relevant Neurological Abnormalities. Neurourol. Urodyn. 36, 259–262 (2017).
Abrams, P. et al. THE STANDARDISATION OF TERMINOLOGY IN LOWER URINARY TRACT FUNCTION: REPORT FROM THE STANDARDISATION SUB-COMMITTEE OF THE INTERNATIONAL CONTINENCE SOCIETY. Urology 1, 37–49 (2003).