Reproducibility of Cystometry in Overactive Detrusor

Abstract

Objective: To examine the reproducibility of cystometry in the overactive detrusor.Methods: The study sample involved 30 patients of the placebo arm in double–blind clinical trials for an overactive detrusor. They had demonstrated detrusor overactivity and underwent the second cystometry after 2–4 weeks. Nonparametric tests for paired data were used to examine the reproducibility of four variables: volume at first desire to void, volume at first involuntary contraction, cystometric capacity, and the maximum pressure of involuntary contraction. Percent change and within–subject standard deviation were calculated to assess intraindividual variability.Results: The second test results showed a significant and systematic change for the better. Volume variables increased by 10–13% (p<0.01), involuntary contraction was not elicited in 3 cases (10%), and the maximum contraction pressure decreased by 18% in the remaining cases. Intraindividual variability was not small. Seventeen patients (57%) demonstrated ≧25% change in one or more variables, and the 95% confidence interval of cystometric capacity, for example, was calculated as (x –57, x +57), where x is a test result. No specific patients’ demographics were found related to variability.Conclusion: Repeat cystometry in the overactive detrusor is not highly reproducible and may be subject to a systematic effect for the ‘better’. Whether this is due to the placebo effect or the learning effect could not be determined.