Is isolated bladder outlet obstruction associated with hydronephrosis? A database analysis

Aims To examine whether isolated bladder outlet obstruction in the absence of associated lower urinary tract abnormality results in hydronephrosis. Isolated obstruction causes a brief rise in bladder pressure that might not trigger hydronephrosis. Methods Data included adult men who underwent urodynamics for refractory non-neurogenic lower tract symptoms between 2011 and 2020. International Continence Society indices for obstruction (bladder outlet obstruction index [BOOI] >= 40) and underactivity (bladder contractility index [BCI] < 100) were calculated. Storage abnormality was defined as detrusor overactivity (DO) or poor compliance (<20 ml/cm H(2)0). Isolated obstruction was defined as BOOI >= 40, BCI >= 100 and no storage abnormality. Nonparametric tests using R program (3.5.0) applied (p < .05 significant). Logistic regression analyses were performed to study the relationships of hydronephrosis with lower urinary tract function. Results A total 1596 men (range, 18-91 years; median, 51.0 years; Q3, 64.0 years; Q1, 34.0 years) were eligible. Hydronephrosis was noted in 274 (17.2%). A total of 45.4% were obstructed, 52.3% were underactive and 41.7% had storage abnormality. Storage abnormality (odds ratios [OR], 2.05; 95% confidence interval [CI]: 1.56, 2.69;p < .001) and bladder contractility (OR, 1.68; 95% CI, 1.25-2.26;p < .001) but not obstruction (OR, 1.07; 95% CI, 0.80-1.44;p = .634) was associated with hydronephrosis. Of eight possible combinations, men with BOO >= 40, BCI >= 100 and storage abnormality had highest probability of hydronephrosis (OR, 0.29; 95% CI, 0.24-0.33). Subanalysis showed that poor compliance (OR, 3.39; 95% CI, 2.49-4.60;p < .001) but not DO was associated with hydronephrosis. Younger age and higher postvoid residual urine were also associated with hydronephrosis. Conclusions In adult men with refractory non-neurogenic lower urinary tract symptoms, isolated bladder outlet obstruction is not associated with hydronephrosis.