Hypothesis / aims of study
Pelvic floor disorders are a hidden epidemic, associated with substantial stress and profound economic burden. Assessment of pelvic floor muscle (PFM) activity is difficult, due to a lack of simple to use and reliable measurement techniques. The Multiple Array Probe Leiden (MAPLe) enables assessment of PFM activity and is capable of differentiating between muscle groups (1). Test-retest repeatability, performed on 20 healthy subjects, turned out to be moderate to excellent (1). Although the MAPLe is already in use in both clinical and research settings, we are unaware of studies examining the reliability of this probe among symptomatic patients. We aimed to evaluate the test-retest reproducibility of the MAPLe in male patients with lower urinary tract symptoms (LUTS).
Study design, materials and methods
Between April and October 2018, consecutive men aged ≥18 and referred to the urology department for moderate to severe LUTS were recruited. After informed consent, men completed symptom scores and underwent standardized physical examination and uroflowmetry. Next, an anal MAPLe measurement was carried out in supine position, according to the manufacturers’ protocol. This included three tasks: one minute rest, maximum voluntary contractions (MVC) and endurance contractions (EC). The summarizing result included a visual display and several variables: mean microvoltage (µV) during rest, and mean µV, maximum (max) µV and onset and offset time during MVC and EC. The urologist decided which treatment was initiated. Irrespective of the treatment choice, all men were re-assessed after approximately 6-8 weeks. For this substudy, we selected men with a wait-and-see approach or α-blocker therapy, assuming that pelvic floor function was not affected in these groups. MAPLe measurements with errors were excluded.
We calculated the average of the two assessments for each outcome, and as a measure of relative variability we estimated the coefficient of variation (CV) as standard deviation/mean*100. Possible systematic errors were visualized using Bland-Altman Plots. Spearman correlation coefficient (SCC) was used to determine correlation, which was categorized as: <0.30 negligible, 0.30-0.50 low, 0.50-0.70 moderate, 0.70-0.90 high and >0.90 very high correlation. Intraclass correlation coefficient (ICC) was used to determine consistency, which was categorized as: <0.50 poor; 0.50-0.75 moderate, 0.75-0.90 good and >0.90 excellent consistency. Due to small sample sizes, data were expressed as median and interquartile range. Statistical analyses were performed using SPSS® version 24.0 for Windows.
The study population included 57 men with moderate to severe LUTS, of whom 10 with wait-and-see and 11 with α-blocker therapy were selected for the test-retest assessment. Table 1 shows patient characteristics and average outcomes for both groups.
In the α-blocker group Bland-Altman plots illustrated systematic error with overall lower max µV and higher onset and offset times during the second measurement. In the wait-and-see group proportional error was shown for EC (mean µV) and MVC (offset time).
Overall, the reproducibility seemed poor according to the CV, SCC and ICC. The outcomes of max µV and onset times particularly showed high variation, low to weak correlation and poor consistency in both groups. On the other hand, the mean µV, especially in rest and EC, showed reasonable variations, moderate to high correlation and moderate to good consistency. The offset time outcomes varied in both treatment groups.
Interpretation of results
This is the first study to examine the test-retest reproducibility of the MAPLe in men with LUTS. Our results showed poor test-retest reproducibility for the majority of outcomes of the MAPLe assessment.
We feel that these results must be interpreted with caution, due to the small sample sizes, which has led to wide confidence intervals. It is yet unclear whether this outcome reflects a true problem with the MAPLe method itself or the influence of other confounding factors. For example, the poor reproducibility might be caused by incorrect PFM contractions during testing and a learning effect of the participants. Another possible confounder is real change in PFM activity over time due to long follow up time and/or treatment.