A comparison of ambulatory and conventional urodynamic studies in men with borderline outlet obstruction

To compare detrusor function and outlet behaviour on ambulatory urodynamic monitoring (AUM) with conventional cystometrography in symptomatic men with borderline evidence of bladder outlet obstruction (BOO), as determined by conventional cystometrography, and to assess the usefulness of AUM in reclassifying this population of patients into obstructed and unobstructed groups.

Sixty-nine consecutive men (mean age 59.6 years) with lower urinary tract symptoms (mean International Prostate Symptom Score 19.1) and borderline BOO on a medium-fill conventional urodynamic study (CUS) were examined prospectively with AUM. Detrusor contractility, obstruction grade, maximal voiding detrusor pressure (pdet(max)), detrusor pressure at peak flow (pdet Qmax) and peak flow rate (Qmax) determined by both methods were compared. The incidence of detrusor instability (DI) detected by both modalities was also evaluated.

There was considerable disagreement between the investigations during the voiding phase. Detrusor contractility was higher on AUM than on CUS (P= 0.003) and obstruction grade was significantly lower on AUM (P=0.018). There was no difference in pdet(max) nor pdet Qmax. The mean (95% confidence interval) Qmax was higher on AUM, at 12.9 (1.3) mL/s, than on CUS, at 8.9 (0.8) mL/s. On the Abrams-Griffiths nomogram the most significant changes were six men (10%) from equivocal to obstructed, seven (11%) from equivocal to unobstructed and two (3%) from obstructed to unobstructed on CUS and on AUM, respectively. Thus, in 24% of patients there was a potentially clinically significant change resulting from the information generated by AUM. DI was identified on CUS in 26 (41%) men and on AUM in 25 (40%); 35 men (56%) had evidence of DI on either AUM or CUS.

The significant disagreement between the findings on CUS and AUM suggests that the conditions under which pressure-flow investigations are carried out significantly affect findings in borderline cases. The reclassification of patients by AUM into obstructed and unobstructed groups occurs in 24% and may be clinically relevant. AUM appears to be complementary to CUS in the assessment of men who are borderline for obstruction on conventional testing, but the clinical implications of this have yet to be determined.