Objective: To compare urodynamic indices of isometric and isotonic detrusor contractile function between patients with idiopathic detrusor instability and patients with multiple sclerosis (MS) and detrusor hyper-reflexia and thus determine whether the different types of detrusor instability share a common pathophysiological pathway.
Patients and methods: Two groups of women were studied; 1139 neurologically normal patients with detrusor instability (mean age 55 years, SD 17) and 141 with multiple sclerosis (MS) and detrusor hyper-reflexia (mean age 45 years, SD 11). Patients were assessed using static water cystometry, examining storage function, isometric and isotonic detrusor contractile function and voiding outflow function.
Results: Bladder capacities were lower in the MS group, with a median of 357 mL, 95% confidence interval (CI) 305-400 mL, compared with the neurologically normal patients (median 450 mL, 95% CI 425-450, P < 0.001, Mann-Whitney U-test). Voiding was incomplete in the MS group, with a median (95% CI) residual volume of 100 (100-125) mL, but complete in the normal group, at 10 (10-10) mL. Higher median (95% CI) detrusor pressures at urethral opening (P(det open)) and closing (P(det close)) were recorded in the MS group than in the neurologically normal group, at 35.5 (33.2-46.6) cmH2O and 30 (27.6-31.6) cmH2O for P(det open), respectively (P = 0.003), and 25.3 (20.9-31.6)cmH2O and 16.6 (15.0-18.1) for P(det close), respectively, (P = 0.001). In the MS group, the median (95% CI) isometric unstable contractions were less well maintained, but were more powerful, at 17.6 (15.6-18.9) N, compared to the neurologically intact group at 14.4 (14.0-14.9) N (P = 0.002). In the MS group, contractions frequently did not relax back to baseline, whereas in the group with detrusor instability, full relaxation after contraction was more usual. There was no significant difference in the maximum speed of detrusor shortening (isotonic activity), measured by the velocity constant Q*, between the groups (median for both groups 20 mL/s, 95% CI 17-23).
Conclusion: These results show differences in storage function, isometric detrusor contractile function and voiding outflow function between detrusor instability and detrusor hyper-reflexia, indicating that the two conditions may not share a common pathophysiological pathway.