Urethral instability: clinical and urodynamic characteristics.

Filling cystometry was performed on 397 patients with lower urinary tract complaints. The overall prevalence of urethral instability was 12.6% (50/397). Of these 187 patients had detrusor instability (DI). Within the DI group, clinical and urodynamic characteristics were compared. Patients with an unstable urethra had a shorter functional urethral length (P = 0.005). For those with DI, 28 of 187 (15%) had urethral instability. Forty (21%) women had a decrease in maximal urethral pressure that preceded the detrusor contraction (type II DI). When those with type II DI were excluded, the difference in functional urethral length was not observed. Patients with type II DI experienced an earlier sensation of fullness of 228 mL compared with 283 mL for the other patients with DI (P = 0.001). There was a positive association between urethral instability and type II DI. Four different patterns of urethral pressure changes were observed. Based on these findings, it appears that a urethral abnormality may be the primary disorder in patients with type II DI. The differentiation of the various subtypes of urethral instability and DI might be important for directing therapy.