Mixed urinary incontinence (MUI) is defined as involuntary urine loss associated with both physical exertion/increased intra-abdominal pressure and with urinary urgency. [1] In females, prevalence estimates of the condition have been observed as increased significantly among women 60 years and older, with a great impact on quality of life. The assessment of MUI is performed on a subjective diagnosis of patients according to their predominant symptom, thus different sub-groups of cases with stress predominant MUI,  urge predominant MUI, and stress and urge MUI equal contributions, can be identified. 
Currently, most of the available studies on women compalining of MUI have used patient's symptoms as index test, without a combination with clinical signs and urodynamic results. [2] In this regard, no consistent information on symptoms of the emptying phase of the bladder and pressure-flow (P/F) study are available in women affected by MUI. 
We investigated voiding symptoms and urodynamics with P/F study in women presenting with MUI, with the detection of predictive variables for the different MUI clinical presentations.

In a national, multicentre, prospective study (Ethics Committee approval obtained), women presenting with a clinical history of MUI were classified into stress-predominant MUI or urge-predominant MUI (S-MUI; U-MUI) or MUI with equal symptoms’ presentations (E-MUI) and underwent physical examination, 3-day voiding diary and urodynamics with pressure flow-study. On pressure-flow study, Projected Isovolumetric Pressure 1 (PIP1; normal range: 30-78 cmH20) and intubated flow Bladder Voiding Efficiency (IF-BVE) investigated detrusor contractility. Detrusor underactivity (DU) was defined as PIP <30 cmH20 and IF-BVE <90 %. Blaivas-Groutz nomogram was used to detect bladder outlet obstruction (BOO).  A multivariate, logistic, regression analysis was applied to identify any predictive variables for the 3 MUI sub-groups.

One hundred forty-four women (with no clinical diagnosis of pelvic organ prolapse) were prospectively evaluated: 74 with S-MUI, 66 with U-MUI, 4 with E-MUI (the latter were excluded from the analysis). Overall, reduced PIP and IF-BEV were observed in 31.2 and 15.6% of cases, respectively. PIP was significantly lower in S-MUI than in U-MUI (Fig. 1). No relationships were found between PIP, IF-BEV and voiding symptoms. 
Predictive variables for reduced PIP were:
urethral hypermobility: OR= 2.23, 95% C.I.= 1.06-4.7, p=0.05;
positive Valsalva Leak Point Pressure: OR=3.01, 95%, C.I=1.34-6.8, p=0.011).

Women with MUI have not negligible proportions of symptoms of the emptying phase of the bladder and reduced detrusor contractility. Overall, reduced values of PIP and BEV %, both indicative of poor detrusor contractility, have been detected in 31.2% and 22% of all MUI cases.  Difference in the two measuring instruments (PIP and BEV%) can explain discrepant detrusor underactivity rates. Women with S-MUI appear to be more affected by DU on pressure-flow study, as compared to those affected by U-MUI.  Reduced PIP appears to be linked to urethral hypermobility and positive VLPP,  both expression of low urethral resistance in cases with S-MUI. Worth of noting, 10.3% of women presenting with U-MUI were diagnosed with BOO on pressure-flow study. All these observations have potential, important clinical implications, although the effects of urodynamics on the clinical outcomes after treatment have not yet been clarified.

Bladder behaviour in MUI is more complex than we previously hypothesized. A detailed clinical evaluation and urodynamics with pressure-flow study appear to be important tools in order to deeply investigate and better understand the pathophysiology underlying MUI different presentations in women.

Haylen BT, Ridder D, Freeman RM, et al. An International Urogynecological Association (IUGA)/International Continence Society (ICS) Joint Report on the Terminology for Female Pelvic Floor Dysfunction. Neurourol Urodyn. 2010;20
Leijsen SAL, Hoogstad-van Evert JS, Willem J. Mol B, et al. The Correlation Between Clinical and Urodynamic Diagnosis in Classifying the Type of Urinary Incontinence in Women. A Systematic Review of the Literature. Neurourol Urodyn 2011; 30:495–502.