Hypothesis / aims of study
A working group of the International Consultation on Incontinence Research Society recently proposed the definition of coexisting overactive–underactive bladder (COUB) as a possible new syndrome [1]. This syndrome is characterized by coexisting storage and emptying symptoms in the same patient, without implying any specific urodynamic/functional findings or causative physiology; and these symptoms are suggestive of urodynamically demonstrable coexistent detrusor overactivity/underactivity but can be caused by other forms of urethro‐vesical dysfunctions. It has been hypothesized that the COUB detrusor is abnormally activated during the filling phase without a complete rest, thus wasting energy required for the next voiding phase, which is then impaired due to muscle asthenia and exhaustion. Aim of this retrospective study was to verify this hypothesis, on data coming from the urodynamic database of a single center.
Study design, materials and methods
We included male patients undergoing urodynamic study (filling and voiding phase included pressure/flow study) at our center between 2011 and 2022. All patients were affected by lower urinary tract symptoms (LUTS). Neurologic disease (multiple sclerosis, stroke/ictus, Parkinson disease or spinal injury) and patients with previous urinary tract surgery were excluded. Urodynamic study (cystometry followed by pressure/flow study) was performed with a 6 Fr catheter and 8 Fr rectal balloon to measure, respectively, bladder pressure (Pves) and abdominal pressure (Pabd). Urodynamic tests had been performed respecting the International Continence Society Good Urodynamic Practices and Terms [2]. Patients were divided in two groups (A and B): patients with normal detrusor function (NDF) and patients with detrusor overactivity (DO) during the filling phase. Number of patients with bladder
outlet obstruction (BOO, defined for a bladder outlet obstruction index, BOOI, >40), number of patients with detrusor underactivity (DU, defined for a bladder contractility index, BCI <100), BCI, voiding efficiency (bladder capacity - post-void residual urine (PVR)/ bladder capacity) and post - voiding residual (PVR) were compared in the two groups. Furthermore, DO patients were divided in two subgroups, according to the volume of appearance of DO (before vs. at or after 200 mL) and mean BCI in these two subgroups was calculated.
Results
We analyzed 202 male patients with LUTS (mean age 63,5 years). Thirty-two (15,84%) patients had long-term urinary catheters and 3 (1,5%) performed clean intermittent catheterization (CIC). Ninety-one patients (45,1%, Group A) showed NDF and 111 patients (54,9% Group B) DO, 83 of them (74,8%) have phasic detrusor contractions and 28 (25,2%) have pre - voiding detrusor overactivity; only 18 (8,9%) men showed DO incontinence. Mean values of filling and voiding parameters are reported in Table 1. During the voiding phase, 90 patients (44,6%) were obstructed (BOOI > 40), 49 (24,2%) were equivocal (20< BOOI > 40) and 63 (31,2%) were not obstructed (BOOI <20). Forty-three (38.7%) and 31 (34%) patients showed BOO in Group A and B, respectively. Thirty-one (27,9%) and 25 (27,5%) patients showed DU in Group A and B, respectively. During the filling phase, 69 (75,8%) patients of the group B showed DO before a filled volume of 200 mL, while 22 (24,2%) patients at a filled volume >200; their mean BCI was 114,7 and 111,5, respectively (p=0,6896).
Interpretation of results
To our knowledge, this is the first study trying to assess possible differences in terms of detrusor contractility in patients with detrusor overactivity or normal detrusor function in the filling phase. In this series, we were not able to find differences between patients with DO or with NDF in terms of detrusor function during the voiding phase. In particular, the number of patients with DU wascomparable in the two groups. The voiding efficiency, PVR and BCI were also comparable in the two groups. These findings seem to contradict the hypothesis that in the COUB, DU could be caused by the wasting of energy used during bladder filling, determining impaired voiding due to muscle asthenia and exhaustion. Further data against this hypothesis come from the observation that BCI is similar in patients with early (before bladder filling of 200 mL) and late appearance of DO. We preferred to use voiding efficiency, instead of voided volume because this last could be influenced by the presence of DO, which may reduce the bladder capacity, as found in this series and in previous studies. It is worthy to note that the number of patients with BOO was also comparable in the two groups, thus not interfering significantly in all the evaluations. Limits of this study are the retrospective design and the presence of only symptomatic patients in this database without a control group of asymptomatic subjects. The strengths of this study are the use of data coming from a single center and urodynamic data obtained following the ICS good urodynamic practices.