Lower urinary tract symptoms (LUTS) significantly impact older adults and are associated with a substantial deterioration in health-related quality of life in this population. The relationship between LUTS and aging is thought to be due, in large part, to aging of the bladder, as a number of changes in bladder function and structure are known to be very common with advanced age. Two urodynamic abnormalities which may commonly underlie a patient’s LUTS, detrusor overactivity (DO) and detrusor underactivity (DU), are both increasingly prevalent with older age. In a subset of patients, DO may coexist in combination with DU (DO-DU). Detrusor overactivity (DO) with detrusor underactivity (DU) (DO-DU) was described as typical of aging (1). Combined DO-DU was first described in older women. This report indicate that non-neurological diseases could cause DO-DU, but other studies show that DO-DU occurred in various neurological diseases (2). The theory of a pathophysiologic progression from DO to DU is supported by growing evidence of common etiological factors between DO-DU, DO, and DU. Nevertheless, the etiology of DO-DU remains poorly understood, and likely involves multiple complex factors. 
Older age is separately related to both DO-DU and comorbidity burden, while neurological diseases are related to both DO-DU and comorbidity burden. It remains unclear whether comorbidity burden is associated with this unique form of lower urinary tract dysfunction in patients with neurological diseases. We aimed to explore potential associations between DO-DU and comorbidity burden in neurologic older women.

The present study is a single center cross-sectional analysis of consecutive female patients who underwent urodynamic evaluation from 2016 to 2019 in a university hospital-based rehabilitative medicine department specializing in geriatrics. 
The participants were community dwelling women who presented for a geriatric assessment and warranted urodynamic evaluation benefited from a same-day urodynamic study, performed by a physiatrist with expertise in functional urology and geriatrics. Inclusion criteria were female gender, age ≥65 years, and presence of neurological pathology. Exclusion criteria were an inability to urinate or a bladder voiding efficiency<5% (defined as the ratio between voided volume and total bladder capacity) or a bladder outlet obstruction on urodynamic assessment.
Participants were categorized as having DO, DU, combined DO-DU, or a negative study. The clinical assessment consisted of a comprehensive medical history and physical examination, as well as and an assessment of mood, cognition, functional performance, nutrition status, mobility, and urinary symptoms. Demographic and medical data including co-morbidities, as measured by the Cumulative Illness Rating Scale (CIRS), were collected. The CIRS-G has been robustly validated and is known to be predictive of hospitalization and mortality among geriatric patients in multiple settings. The association between DO-DU and comorbidity burden, was assessed in univariate analysis.

A total of 185 women aged ≥65 years underwent urodynamic evaluation during the study period, of whom 103 were excluded due to the absence of neurological disease. Correspondingly, sixty-one women met the criteria for inclusion in the analysis (Figure 1). Median participant age was 72 (69-77) years, 57 patients (93%) had a central nervous system disease, and the median CIRS-G score was 7(5-9) (Table 1). The most common neurological pathology was stroke (31%). Among included subjects, the most frequent complaint that led to the urodynamic assessment was urgency urinary incontinence (34%). The most common urodynamic diagnosis was DO (36%), followed by DU (26%), negative urodynamic study (21%), and DO-DU (16%). On univariate analysis, there was no significant association between urodynamic diagnosis, age or comorbidity burden measured by the CIRS-G. Voiding symptoms assessed by urinary symptom profile score were significantly more severe in patients with DU.

The data do not show any significant differences between this urodynamic diagnosis and comorbidity burden or age. We cannot conclude on the existence of an association between comorbidity burden and DO-DU in our specific population. 
The outcome of the study may be explained by a low statistical power, which may be related to a small sample size. The number of patients excluded, for no voiding or uninterpretable voiding, was significant. The main explanation for these exclusions is that the conditions of the urodynamic study were not those of normal voiding. Another explanation could be related to the pathophysiology of DO-DU which could be explain by the impairment of several neurological functions. Indeed, DO-DU could be related to multiple factors rather than a single factor. In the CIRS-G, neurological pathology is a maximum 4-point item. The CIRS may not be the ideal tool to use in these patients with neurological pathologies and perhaps another tool reflecting the patient's disability, such as the frailty index, might be more interesting to use. In addition, data were obtained from a specialized, geriatric-focused practice, such that the observed associations may differ in a primary care or inpatient hospital setting, as well as among younger patient populations. Thus, the comorbidity burden would also be less important in our study population than in another geriatric population. Afterwards, patients referred to our department are often followed by physicians, implying a probable better management of their comorbidities and thus a lower CIRS. One possible explanation is that there is no association between DO-DU and age or comorbidity burden, and the neurological pathology would explain all alone the LUT dysfunction. However, in studies on Parkinson's disease, there is an association between duration of the disease and urodynamic diagnosis, which suggests that age plays a role in the association between DO-DU and neurological diseases (3).

We cannot conclude that increased cumulative medical comorbidity burden is predictive of combined DO-DU in the older neurological population. Although DO-DU is more common in older and neurological populations, associations between DO-DU and age or comorbidity burden were not found. Several hypotheses can explain this negative result notably a low statistical power due to the small sample size of the population. The pathogenesis of DO-DU is likely more complex than chronological aging alone and merits further study. This study is part of a desire for a better understanding of DO-DU to improve its treatment.

Resnick NM and Yalla SV: Detrusor hyperactivity with impaired contractile function. An unrecognized but common cause of incontinence in elderly patients. JAMA 1987; 257: 3076–3081
Yamamoto T, Sakakibara R, Uchiyama T, et al: Neurological diseases that cause detrusor hyperactivity with impaired contractile function. Neurourol Urodyn 2006; 25: 356–360
Uchiyama T, Sakakibara R, Yamamoto T, et al: Urinary dysfunction in early and untreated Parkinson’s disease. J Neurol Neurosurg Psychiatry 2011; 82: 1382–1386

Continence 2S2 (2022) 100477
DOI: 10.1016/j.cont.2022.100477