Study design, materials and methods
Study designg
Prospective cohort study
Materials and methods
In this prospective study between January 2015 and September 2017, we recruited 170 patients with MS who underwent a videourodynamic study with selective sphincter EMG due to lower urinary tract symptoms (LUTS). A follow-up of a year was carried out and finally 114 patients (84 women [74%] and 30 men [26%]; mean age (± standard deviation) 49 ± 10.0 years, finished the study.
Sample size was calculated based on the data provided by Wiedemann et al. [1] and Bemelmans et al. [ 2]. Assuming an Expanded Disability Status Scale (EDSS) score difference of 1.5 points, a standard deviation (SD) of 2.36 points, an alpha level of 5%, and a statistical power of 80%, the minimum sample size was calculated at 37 patients per group.
MS was diagnosed by the Hospital’s Neurology Department. We comprehensively reviewed patients’ clinical histories, recording data on demographic, neurological (including level of disability, measured using the EDSS and urological variables (including presence and type of LUTS and rUTIs). Recurrent urinary tract infections were diagnosed according to the criteria of the European Association of Urology. Thirty-seven patients (32%) had rUTIs.
The videourodynamic study and selective sphincter EMG were performed in accordance with the specifications of the International Continence Society (ICS) and guidelines for Good Urodynamic Practice.
For statistical analysis we used the Fisher exact text and the chi-square test for qualitative variables and the t-test to compare the means of parametric data. Quantitative data were tested for normal distribution using the Kolmogorov-Smirnov test. Statistical significance was set at P < 0.05.
Results
Relationship between clinical variables and rUTI occurrence.
Statistically significant differences were observed for symptom progression time (longer in patients with rUTIs), MS duration (longer in patients with rUTIs), EDSS score (higher in patients with rUTIs), and MS type (greater rUTI frequency in primary progressive MS and secondary progressive MS).
Relationship between videourodynamic findings and rUTI occurrence.
Significant differences were observed in maximum flow rate (lower in patients with rUTIs), voided volume (lower in patients with rUTIs), bladder voiding efficiency (greater post-void residual volume in patients with rUTIs), Stress Urinary Incontinence (SUI) (greater rUTI frequency in patients with SUI), detrusor pressure at maximum flow (lower in patients with rUTIs), and BCI score (lower in patients with rUTI).
No statistically significant differences were observed between between neurourological findings and rUTI occurrence
Interpretation of results
Our study identified a series of clinical and urodynamic risk factors for rUTIs.
Clinical risk factors were symptom progression time (longer in patients with rUTIs), MS duration (longer in patients with rUTIs), EDSS score (higher in patients with rUTIs), and MS type (greater rUTI frequency in patients with PPMS and SPMS).
Regarding to urodynamic risk factors, reduced flow rate and bladder voiding efficiency may be secondary to impaired detrusor contractility or to bladder outlet obstruction. The fact that patients with rUTIs had lower detrusor pressure at maximum flow, similar BOOI to those of patients without rUTIs, and significantly lower BCI suggests that impaired detrusor contractility is the main functional risk for the voiding phase.
We also observed that patients with SUI displayed a significantly higher frequency of rUTIs. This is probably also related to detrusor contractility. Valentini et al. [3] observed a direct correlation between detrusor contractility and urethral resistance (which is related to SUI); patients with SUI would have lower urethral resistance and therefore impaired detrusor contractility. Therefore, the greater frequency of rUTIs in patients with SUI would also be explained by impaired detrusor contractility.