Lower urinary tract symptoms are common in patients with multiple sclerosis (PwMS). The main symptom is overactive bladder (OAB), characterized by urgencies, with or without urinary incontinence. Different mechanisms can lead to OAB in PwMS; detrusor overactivity is usually cited as the main one, however, impaired bladder sensations are also reported. Although assessment of bladder sensations is highly recommended, definitions of increased or decreased bladder sensations remain unclear, and the relationship between bladder sensations and the severity of bladder symptoms has been poorly studied(1). 

The aim of the study was thus to assess the relationship between bladder sensations during cystometry and the severity of overactive bladder symptoms. The second aim was to assess the impact of detrusor overactivity on bladder sensations.

Consecutive PwMS assessed with a standardized urodynamic test including 3 consecutive cystometries (20 ml/min, 100 ml/min and 100 ml/min with 4°C fluid (Ice water test (IWT))) between June 2020 and October 2022 were included in this retrospective study. Data collected were bladder diaries including an assessment of desire to void for each micturition, symptoms assessed with Urinary Symptoms Profile (USP), bladder sensations with first desire to void (FDV) and strong desire to void (SDV) during the 20ml/min cystometry, and presence of detrusor overactivity (DO) during at least one of the three cystometries. As no clear thresholds for earlier or delayed bladder sensations are defined, the volume between FDV and SDV was calculated for each patient (FDV-SDV) and used as a marker of bladder sensations assessment.

As DO has been previously described to impact bladder sensations, this hypothesis was verified first, and subgroup analyses on patients without DO were performed secondarily to assess the relationship between bladder sensations and OAB symptoms severity. 
Comparisons between patients with and without DO were performed using Welch t-tests or Wilcoxon rank tests. Correlations between bladder sensations and severity of overactive bladder symptoms were performed using Spearman correlations. Significance was taken as p < 0.05.

Two hundred and two patients were included (mean age 47.4±11.8 years, median EDSS 3 IQR [2-5], 74.3% of women). DO was found in 104 (51.5%) patients. Reduced FDV-SDV volume (<50 ml) was significantly associated with the occurrence of DO (27% vs 5%; p < 0.0001), and DO was associated with earlier sensations during cystometries (167±88ml vs 204±109ml for FDV, p=0.02; 285±131ml vs 353±116ml for SDV, p<0.001). The absence of cold perception during IWT was associated with DO (45% vs 23%, p<0.01). The proportion of micturitions done at urgent need to void on bladder diaries was not different between the two groups (26% for those without DO vs 28% for those with DO, p=0.69).

In patients without DO, FDV-SDV volume was correlated with voids frequency on bladder diaries (rho = -0.30; p=0.03), mean voided volume (rho = 0.52; p<0.001), and USP OAB sub-score (rho=0.32; p<0.01), especially with the item related to the warning time (time from first sensation of urgency to micturition or incontinence) (rho = 0.38; p<0.01) (Table1).

DO is associated with earlier bladder sensations, and the impact of DO on bladder sensations has been previously highlighted(2). However, in patients without DO, bladder sensory disorder is one of the mechanisms that could lead to OAB. Assessing the course of bladder sensations during noninvasive bladder filling, differences have been demonstrated between healthy volunteers and non-neurogenic patients with OAB(3). 
The definition of earlier or delayed sensations remains unclear, and the delay between FDV and SDV can play a role in OAB symptoms. We demonstrated a correlation between FDV-SDV and the warning time. This correlation is weak, probably because other factors impact the warning time as mobility impairment, emotions (such as fear to experience incontinence), and other sensory bladder parameters (delay of FDV, course of bladder sensations, number of different levels of bladder sensations, etc.).

Detrusor overactivity has an impact on bladder sensations during cystometries. In patients without detrusor overactivity, afferent bladder sensation disorders may have a significant impact on overactive bladder severity, especially in reducing the warning time.

Gajewski JB, Schurch B, Hamid R, Averbeck M, Sakakibara R, Agrò EF, et al. An International Continence Society (ICS) report on the terminology for adult neurogenic lower urinary tract dysfunction (ANLUTD). Neurourol Urodyn. 2018;37(3):1152-61.
Pfisterer MHD, Griffiths DJ, Rosenberg L, Schaefer W, Resnick NM. The impact of detrusor overactivity on bladder function in younger and older women. J Urol. mai 2006;175(5):1777-83; discussion 1783.
Heeringa R, van Koeveringe GA, Winkens B, van Kerrebroeck PEV, de Wachter SGG. Do patients with OAB experience bladder sensations in the same way as healthy volunteers? A focus group investigation. Neurourol Urodyn. avr 2012;31(4):521-5.