Women with symptoms of voiding dysfunction may be associated with detrusor underactivity (DU) or bladder outlet obstruction (BOO). The treatment strategies are different between DU and BOO. In general, urodynamic/videourodynamic studies are important for differential diagnosis. However, urodynamic/videourodynamic studies are invasive. We are interested whether there were specific symptoms or measurements that can be used for initial differential diagnosis between DU and BOO. Thus, the aim of this study is to (1) elucidate the prevalence of DU and BOO in each age group and (2) elucidate the clinical and urodynamic differences between the DU, BOO and non-DU/BOO groups.

Between April 1996 and September 2018, all women with symptoms of voiding dysfunction who visited the urogynecological department of a medical center for urodynamic evaluation were reviewed. Those women who have no complete data of maximum flow rate (Qmax), voided volume, post void residual volume (PVR) and detrusor pressure at maximum flow rate (PdetQmax) were excluded from this study. Besides, women with cystocele were also excluded. The DU was defined when the PdetQmax was less than 20 cmH2O, the Qmax was less than 15 mL/s, and the bladder voiding efficiency (BVE) was less than 90 % [1]. The BOO was defined when the PdetQmax was not less than 40 cmH2O, and the Qmax was less than 12 mL/s [1]. BVE = voided volume / (voided volume + PVR) x 100%. Those women without DU or BOO were allocated to the non-DU/BOO group.
STATA software was used for statistical analysis. ANOVA test with Bonferroni correction or chi-square test were used for statistical analysis as appropriate. Linear regression analysis with age adjustment was used to assess the adjusted effect of variables. P < 0.05 was considered as statistically significant.

A total of 602 women were included in this study. One hundred (16.6%) women were found to have DU, and 60 (10%) women were found to have BOO. The highest rate (39%, 7/18) of DU was in the age of more than 81 year-old, and the highest rate (17%, 8/47) of BOO was found in the age between 31 and 40 year-old. 
ANOVA analysis revealed that women in the DU group were older (60.6±13.4  vs. 53.2±14.0 years, p=0.002), and had higher parity (3.1±1.6 vs. 2.4±1.8, p=0.02), lower PdetQmax (11.9±5.7 vs. 62.5±40.7 cmH2O, p<0.001), lower maximal urethral closure pressure (MUCP, 70±42 vs. 93±42 cmH2O, p<0.001) and lower functional profile length (3.0±1.3 vs. 3.5±1.3 cm, p=0.037), compared with the BOO group. After adjusting with age, the coefficient of DU (coefficient = -13.2 cmH2O, p=0.04) remained significant for predicting MUCP, compared with BOO.
Besides, women with DU were older (60.6±13.4 vs. 56.7±13.3 years, p=0.03) and had a lower Qmax (9.5±3.4 vs. 18.2±7.7 mL/s, p<0.001), lower voided volume (183±121 vs. 291±142 mL, p<0.001), higher PVR (124±117 vs. 83±84 mL, p<0.001), lower PdetQmax (11.9±5.7 vs. 58.5±30.1 cmH2O, p<0.001), compared with the non-DU/BOO group.  After adjusting age, the coefficient of DU remained significant for predict voided volume (coefficient of DU = -100 mL for voided volume, p<0.001) and PVR (coefficient of DU = 39 mL for PVR, p<0.001). 
Women with BOO were had a lower Qmax (8.4±2.1 vs. 18.2±7.7 mL/s, p<0.001), lower voided volume (140±118 vs. 291±142 mL, p<0.001), higher PVR (124±118 vs. 83±84 mL, p=0.006), lower strong-desire volume (224±110 vs. 289±100 mL, p=0.003), higher PdetQmax (62.5±40.7 vs. 58.5±30.1 cmH2O, p<0.001) and higher MUCP (93±42 vs. 76±35 cmH2O, p<0.001), compared with the non-DU/BOO group.
However, there were no differences in the Urgency Severity Scores, Overactive Bladder Symptoms Scores, Urogenital Distress inventory short form scores, Incontinence Impact Questionnaire, severity of bladder problems in the King’s Health Questionnaire (i.e., frequency, nocturia, urgency, urgency incontinence, stress urinary incontinence, nocturnal enuresis, intercourse incontinence, urinary tract infection, bladder pain and voiding difficulty), all domains in the King’s Health Questionnaire (i.e., general health perception, incontinence impact, role limitations, physical limitations, social limitations, personal relationships, emotion, sleep/energy and severity measures) and bladder diary variables (i.e., nocturia episodes, daytime frequency episodes, urgency episodes, incontinence episodes, total voided volume, total fluid intake and maximum voided volume per micturition) between the DU, BOO and non-DU/BOO groups.

Women with DU had a lower MUCP, compared with BOO. Besides, women with DU had a lower voided volume and higher PVR, compared with non-DU/BOO.  In addition, women with BOO had a lower voided volume, higher PVR, lower strong-desire volume and higher MUCP, compared non-DU/BOO. However, there were no differences in the lower urinary tract symptoms and bladder diary parameters between the DU, BOO and non-DU/BOO groups.

About 16.6% of women with symptoms of voiding dysfunction were found to have DU, and 10% of them were found to have BOO. There were some differences in urodynamic findings between the DU, BOO and non-DU/BOO groups. However, there were no differences in lower urinary tract symptoms and bladder diary parameters between the DU, BOO and non-DU/BOO groups, and thus it is difficult to use lower urinary tract symptoms and bladder diary as a tool for differential diagnosis between the DU, BOO and non-DU/BOO groups.

Gammie A, Kaper M, Dorrepaal C, Kos T, Abrams P. Signs and Symptoms of Detrusor Underactivity: An Analysis of Clinical Presentation and Urodynamic Tests From a Large Group of Patients Undergoing Pressure Flow Studies. Eur Urol 2016;69:361-9