**2. Results**

In total, 192 patients received intravesical BoNT-A injections for refractory OAB symptoms during the study period. During the administration of injections, 65 (33.9%) patients were classified into the elderly group ( ≥75 years old), and the remaining 127 (66.1%) patients were classified into the young group. For the young and elderly groups, the mean age was 58.8 ± 11.9 and 82.0 ± 4.6 years old, respectively. A higher percentage of males was found in the elderly group compared to the young group (75.5% and 34.6%, respectively). More comorbidities were found in the elderly group, including hypertension, diabetes mellitus (DM), dementia, coronary artery disease, and chronic kidney disease. The multichannel urodynamic parameters for baseline bladder function prior to BoNT-A injection are listed in Table 1. For the filling phase parameters, the elderly bladders are more sensitive to filling, and have a smaller cystometric bladder capacity (CBC) compared to those of the young. For the voiding phase parameters, a higher detrusor pressure at the maximal flow rate (PdetQmax), a slower maximum flow rate (Qmax), and a smaller voided volume (VV) were found for the elderly group compared to the young group.

Primary outcomes after intravesical BoNT-A injections are shown in Table 2. At 6 months after the injection, 77.2% and 84.6% of patients in the young and elderly group remained subjective success, respectively. The subjective success rate was comparable in both groups at 3, 6, and 12 months after the injections. Additionally, more than 60% of patients in both groups experienced a certain period of subjective dryness without any urge incontinence. Compared to the baseline uroflowmetry parameters, the CBC and PVR were significantly increased, and the voiding efficiency was significantly decreased in both groups three months postoperatively. In addition, the postoperative CBC and VV were smaller, and Qmax was slower (265.8 ± 126.0 vs. 332.5 ± 158.1 mL, *p* = 0.010; 156.9 ± 106.1

vs. 220.4 ± 139.6 mL, *p* = 0.007; and 11.0 ± 7.3 vs. 15.5 ± 10.7 mL/s, *p* = 0.007, respectively) in the elderly group than in the young group. The prevalence of unfavorable outcomes such as a large PVR, urinary retention, and UTI did not vary between groups. For the young and elderly group, 29 (22.8%) and 18 (27.7%) patients were found to have large PVR, and 11 (8.7%) and 8 (12.3%) patients eventually experienced urinary retention and required catheterization to empty the bladder, respectively. Indwelling Foley catheters were used for all the 11 patients in the elderly group and 4 patients in the young group. Clean intermittent catheterization was used by the other 4 patients in the young group. The catheterization period persisted within one week for 7 patients, between one week to one month for 5 patients, and up to two months for 7 patients. Additionally, 18 (14.2%) and 6 (9.2%) patients in the young and elderly group experienced UTI, respectively.

**Table 1.** Patient demographics and baseline multichannel urodynamic parameters.


CAD: coronary artery disease; CBC: cystometric bladder capacity; CHF: congestive heart failure; CKD: chronic kidney disease; CVA: cerebrovascular accident; DM: diabetes mellitus; FS: full sensation; FSF: first sensation of filling; No.: number; PdetQmax: detrusor pressure at the maximal flow rate; PVR: post-void residual urine volume; Qmax: maximum flow rate; SD: standard deviation; US: urge sensation; VV: voided volume.

**Table 2.** Primary outcomes and unfavorable outcomes after intravesical BoNT-A injection.



**Table 2.** *Cont.*

CBC: cystometric bladder capacity; No.: number; PVR: post-void residual urine volume; Qmax: maximum flow rate; SD: standard deviation; UTI: urinary tract infection; VE: voiding efficiency; VV: voided volume. \* Wilcoxon signed-rank test *p* < 0.001 at 3 months compared to baseline.

Table 3 shows the baseline clinical characteristics and multichannel urodynamic parameters of elderly patients with or without postoperative unfavorable outcomes: 6 (9.2%), 18 (27.7%), and 8 (12.3%) patients in the elderly group had postoperative UTI, large PVR, and urinary retention, respectively. For baseline multichannel urodynamic parameters, patients with postoperative UTI tended to have lower bladder compliance (19.7 ± 12.5 vs. 61.0 ± 67.3 mL/cmH2O, *p* = 0.014) and a higher PdetQmax (56.2 ± 33.2 vs. 29.0 ± 17.4 cmH2O, *p* = 0.013) compared to those without UTI, whereas patients with postoperative large PVR or with urinary retention tended to have higher PdetQmax (40.1 ± 23.4 vs. 28.3 ± 18.6 cmH2O, *p* = 0.029; 55.5 ± 27.1 vs. 28.2 ± 17.3 cmH2O, *p* = 0.001, respectively) compared to those with normal PVR or without urinary retention. Regarding underlying comorbidities, patients with postoperative UTI had a higher prevalence of dementia, while patients suffering postoperative urinary retention had a greater prevalence of DM and cerebrovascular accidents.

For the elderly population, multivariate analysis revealed that female, lower baseline bladder compliance, and higher PdetQmax were significantly associated with postoperative UTI. In addition, a higher baseline PdetQmax and a history of DM were associated with urinary retention. However, the association between higher baseline PdetQmax and postoperative large PVR failed to achieve significance (OR: 1.027, *p* = 0.075) after adjusting for age and gender (Table 4).

Forty-three (33.9%) patients in the young group and 14 (21.5%) patients in the elderly group received subsequent injection cycles after the initial BoNT-A effect vanished, whereas the other 135 (70.4%) patients received only one episode of BoNT-A injection. The injection cycles between young and old patient groups are shown in Table 5.


**Table 3.** Baseline clinical characteristics and multichannel urodynamic parameters in elderly population with or without each unfavorable

by mean ± standard deviation or number (%).


**Table 4.** Univariate and multivariate logistic regression to identify factors associated with each unfavorable outcome in elderly population.

post-void residual urine; UTI: urinary tract infection. \* Univariate logistic regression *p* < 0.05. \*\* Multivariate Binary logistic regression.


**Table 5.** The subsequent BoNT-A injection cycles during the follow-up period after the first time BoNT-A injection for young and elderly patients with refractory overactive bladder.
