A term “co-existent overactive-underactive bladder (COUB)” has been proposed to describe a condition in which overactive bladder (OAB) and underactive bladder (UAB) coexist [1]. Few studies have investigated factors associated with COUB, as the definition of UAB has not been established. In this study, we explored factors associated with COUB determined by OAB symptom score and the definition of UAB proposed by a working group of the International Continence Society.

An internet survey on lower urinary tract symptoms was conducted among 6,210 adults. Participants were categorized into COUB, OAB alone, UAB alone, and non-OAB/UAB groups. OAB was diagnosed referring to the OAB symptom score definition [2]. UAB was defined as the presence of all three voiding symptoms (i.e., a slow urinary stream, hesitancy, and straining to void) in the definition proposed by the International Continence Society working group [3]. COUB was defined as the presence of both OAB and UAB. The non-OAB/UAB group means participants who do not meet any of the COUB, OAB, or UAB criteria. Participants’ characteristics and the cumulative number of deficits summing up comorbidities were compared among the four groups. Moreover, nominal logistic regression analysis explored factors associated with COUB.

The prevalences of COUB, OAB alone, and UAB alone in men were 4.3%, 9.6%, and 5.0%, respectively, and in women, 1.6%, 8.2%, and 2.4%. For both genders, mean age, the proportion of comorbid conditions, and the mean cumulative number of deficits differed significantly among the groups (p <0.001), with COUB being the oldest (64 and 74 years old, respectively), highest rate, and highest number (7.0 and 7.8, respectively) (Table 1). On multivariable analysis (Table 2), age (odds ratio [OR] 1.02), frailty (OR 1.98), affective/sleep disorders (OR 2.94), benign prostatic hyperplasia (OR 4.38), and erectile dysfunction (OR 1.79) were independent factors associated with COUB in men (p <0.05), while age (OR 1.04), frailty (OR 4.88), cardiorenal disorders (OR 2.83), neurological disorders (OR 3.04), anorectal dysfunction (OR 2.90), parity ≥3 times (OR 2.96), and pelvic organ prolapse (OR 4.83) were independent factors in women (p <0.05). The results were generally similar when participants with benign prostatic hyperplasia and pelvic organ prolapse were excluded from the analyses.

COUB are potentially developed as a result of ageing and the accumulation of deficits. Moreover, there may be gender differences in factors involved in male and female COUB. The study is limited by the inherent limitations of internet-based surveys, including limited coverage and self-selection bias. In addition, there was no information available on treatment, potentially affecting lower urinary tract symptoms, for comorbidities, and there are no established diagnostic criteria for UAB. The possible inclusion of participants with bladder outlet obstruction in the COUB as well as UAB alone groups is also a profound limitation.

COUB may be a distinct pathology rather than a transitional form from OAB to UAB. The presence of COUB should be kept in mind when treating elderly patients with multimorbidity.

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