Hypothesis / aims of study
Various patterns of detrusor overactivity (DO) have been described in literature[1, 2], and their clinical relevance have been discussed by the ICI-RS 2018.[3] This group stated that the patterns of DO need new definitions based on the stage of filling at which DO occurs, and on the shape and frequency content of an individual DO wave. Precise boundaries for these definitions have, however, not been included in the ICI-RS manuscript. To be clinically relevant, the patterns of DO should be reproducible and unambiguous. The goal of this study therefore is to assess the usability of the definitions of the patterns of DO mentioned by the ICI-RS 2018 and to explore the comprehensiveness required for future definitions. Furthermore, the incidence of these patterns in a historical cohort of urodynamic studies (UDS) are described.
Study design, materials and methods
This retrospective study in a tertiary hospital included all ICS standard UDS (PMID: 27917521) performed in the year 2021 on patients with a minimum age of 18 years. Patients with augmentation cystoplasties were excluded. All UDS were performed using the Nexam Pro (MMS/Laborie, Portsmouth, NH) with a water-filled system and filling rate of 10% of the largest voided volume (bladder diary) per minute.
One investigator scored all DO patterns and categorized patient’s clinical diagnosis to one of ten groups (Table 1). The following DO patterns were defined, either by the investigator or otherwise by their most recent definition in literature: 1: Absent: no DO contractions; 2: Phasic (cited): ‘characteristic wave form and may or may not lead to urinary incontinence’[1]; 3: Terminal (cited): ‘detrusor contraction occurring near or at the maximum of cystometric capacity, which cannot be suppressed, and results in incontinence or even reflex bladder emptying’[2]; 4: Compound (cited): ‘phasic detrusor contraction with a subsequent increase in detrusor and base pressure with each subsequent contraction’[2]; 5: Sustained (cited): ‘continuous detrusor contraction without returning to the detrusor resting pressure’[2]; 6: Other: patterns that do not meet the criteria listed above. Other types mentioned in literature are: a single contraction that is not terminal, or multiple sporadic contractions that are not phasic)[3]; 7: Undefinable: patterns that could not be properly measured e.g. due to a disturbed detrusor pressure trace. After-contraction[3] was not scored in this study.
In this study, two investigators achieved consensus on what constitutes the 'characteristic wave form' mentioned in the definition of phasic DO (2). Consensus was that the wave frequency in a phasic pattern does not have to be exactly constant (i.e. time intervals between waves may vary but an exact cut-off was not defined, a factor 2 variation was decided to be too large). A pattern can only be phasic after three waves due to the frequency constraint (e.g. two waves was scored as ‘other’), and wave amplitude in a phasic pattern may vary (e.g. the amplitude of the final wave increases significantly and terminates the filling phase). Regarding the definition of terminal DO (3): if a patient reports strong desire during a contraction or cannot suppress the contraction it is practice in our hospital to give permission to void to prevent over-inhibition or incontinence. These cases were scored as ‘Terminal DO’ in this study. It was agreed that only one pattern of DO can exist per UDS.
First the absence of DO was extracted from the urodynamic diagnosis in written UDS reports in the hospital’s patient management system. The UDS where DO was present were subsequently scored by examining the cystometry graphs at a time scale of 10 minutes per landscape A4 page and a pressure scale of 0 to 100cmH2O. The investigator scored high pressure DO (yes/no) if the detrusor pressure exceeded 40cmH2O at any point during DO. The investigator also scored UDS quality (good/average/poor), presence of hindering rectal activity on the abdominal pressure trace which obscured the pattern of DO (yes/no), concurrent loss of compliance (yes/no), decision certainty (yes/no) and recorded any considerations during decision making.
Results were analyzed using Excel 2016 (Microsoft, Redmond, WA) and presented using descriptive statistics.
Results
In total 391 UDS of 380 patients were included after the exclusion of 11 UDS. DO was absent in 163 UDS (43% of total). DO pressure patterns were undefinable in 16 UDS due to hindering rectal activity (6) and/or poor measurement quality (12). The relative distribution of the remaining 212 patterns of DO was: 31% phasic, 31% terminal, 10% compound, 6% sustained, and 22% other. The incidence of ten clinical diagnosis categories in each pattern of DO are given in Table 1. DO pressures were high in 43% of phasic, 51% of terminal, 43% of compound, 69% of sustained and 31% of other patterns. Often a high pressure phasic pattern had a relatively large increase in amplitude for the last contraction, which then terminated the filling phase.
For UDS where DO was present, the investigator was unsure of the chosen pattern of DO in 97 cases. Besides hindering rectal activity (21) and suboptimal measurement quality (26), the definitions and agreed upon interpretations of DO patterns were sometimes still too ambiguous to apply to certain UDS. Most often the distinction between a phasic or other (i.e. multiple sporadic contractions) pattern was challenging to make because the wave frequency was not constant.
Interpretation of results
The most recent definitions of the ICI-RS 2018 patterns of DO are usable, but not unambiguous. Phrases like 'characteristic wave form' are open for interpretation, and therefore cause uncertainty during their application. The usability and reproducibility of these patterns of DO could be improved by objectifying their definitions. Characteristics of phasic wave forms should be described in terms of ranges of frequencies and amplitudes. Furthermore, we propose to include in the definition of terminal DO that the contraction terminates the filling phase, regardless of incontinence.
Application the current definitions in a historical UDS cohort showed some notable results. As expected based on figure 1 in ICI-RS 2018, most sustained patterns had a high pressure, but high pressures also occurred >40% in phasic, terminal and compound patterns meaning no pattern was inherently spared. The incidence of clinical diagnosis categories in each pattern of DO can help form hypotheses on their clinical relevance. Phasic and terminal patterns included UDS from all reported patient categories, with the phasic pattern containing relatively more neurogenic patients (notably spina bifida) and the terminal pattern containing relatively more male LUTS and post-prostate intervention incontinence. Furthermore, compound patterns only occurred in males or patients with neurogenic dysfunction and sustained patterns almost only occurred in patients with a neurogenic dysfunction.