To determine the clinical and urodynamic differences in the presentation and the value of simultaneous fluoroscopy in dysfunctional voiding (DV) and primary bladder neck obstruction (PBNO); the 2 most common causes of non-neurogenic “functional” bladder outlet obstruction in women.

A review of our urodynamic study database (March 2003 to August 2009) was conducted. DV was diagnosed when increased external sphincter activity was found during voluntary voiding on electromyography (EMG) or fluoroscopy. PBNO was diagnosed when a failure of bladder neck opening was noted on fluoroscopy during voiding. The demographics, symptoms, and urodynamic study parameters were collected. Comparisons were done using chi-square and 2-tailed t-tests.

DV was diagnosed in 34 women and PBNO in 16. The patients with DV were younger than those with PBNO (40.9 vs 59.2 years, P < .001). Women with DV showed a clinical trend toward having more storage symptoms than those with PBNO and fewer voiding symptoms. Patients with DV had a greater mean maximal flow rate (12 vs 7 mL/s, P = .027) and lower mean postvoid residual urine volume (125 vs 400 mL, P = .012). No significant differences were found in maximal detrusor pressure, detrusor pressure at maximal flow rate, or detrusor overactivity. EMG showed increased activity during voiding in 79.4% of those with DV and 14.3% of those with PBNO (P < .001).

Clinically, women with DV and PBNO had similar presentations, although those with PBNO had poorer emptying. The flow rates and patterns seemed to differ between those with DV and PBNO, although the voiding pressures were similar. EMG alone would have given the wrong diagnosis in 20.6% of those with DV (false negative) and 14.3% of those with PBNO (false positive). When fluoroscopy is used to define these entities, the accuracy of EMG to differentiate them is questionable.