Does the method of cystometry affect the incidence of involuntary detrusor contractions? A prospective randomized urodynamic study

The International Continence Society (ICS) defines overactive detrusor as "one that is shown objectively to contract during the filling phase while the patient is attempting to inhibit micturition." The aim of the present study was to assess whether instructing the patient neither to try void nor to inhibit micturition during filling cystometry may improve the detection rate of involuntary detrusor contractions (IDCs). Forty-two consecutive patients (mean age 65 ± 13.5 years), referred for urodynamic evaluation of persistent irritative lower urinary tract symptoms were prospectively enrolled. All patients were presumed, by history, to have IDCs. Cystometry was performed twice at the same session, each time by using randomly different instructions: Method 1, patients were instructed to try to inhibit micturition during bladder filling; and Method 2, patients were instructed to neither try to void nor try to inhibit micturition, but simply report his or her sensations to the examiner. The occurrence, as well as the urodynamic characteristics of IDCs, were analyzed separately and compared between the two filling methods. Method 1 identified only 20 cases of IDCs, while Method 2 identified 27 cases (48 versus 64% of the study population, respectively; P = 0.02). Analysis of urodynamic characteristics revealed a clear trend of reduced bladder volume at which IDCs occurred when patients were instructed to neither try to void nor to inhibit micturition during bladder filling; however, statistical significance was not established (189 ± 122 versus 240 ± 149 mL, respectively; P = 0.13). All other urodynamic characteristics of IDCs were similar in both methods. In conclusion, better detection rates of IDCs were achieved by instructing the patient to neither try to void nor try to inhibit micturition, but simply report his or her sensations to the examiner, during filling cystometry. If the patient is instructed to inhibit micturition during bladder filling - about 26% of the IDC cases are misdiagnosed.