Detrusor underactivity (DUA) might be the cause of voiding symptoms in some patients; nevertheless its pathophysiology is still under debate. The main objective of our study was to describe the clinical profile and long term follow up of patients with urodynamic diagnosis of DUA without initially Clean Intermittent Catheterization (CIC) requirement. As secondary objective we tried to identify risk factors for starting CIC in patients with neurogenic or non-neurogenic DUA.

This is a retrospective, longitudinal, descriptive, single-centre study of a cohort of male patients with urodynamic proven DUA (ICS 2002 definition and/or Bladder Contraction Index (BCI)<100) between 2008 and 2018. All of this patients adopted a conservative watchfull-waiting policy
As demographic variables we included age, ethiology (non-neurogenic or neurogenic) and symptomatology. In all patients we performed a urodynamic study according to the Good Clinical Practice Guidelines for Urodynamic Studies. Urodynamic variables included were: Qmax, Voided volume, Post voiding Residual Volume (PVR) and voiding efficiency (in Free Uroflowmetry calculated as voided volume/bladder capacity expressed as a percentage). In the P/Q study: Qmax. Urethral opening pressure (Pdet.uo), detrusor pressure at maximum flow (Pdet.Qmax) and BCI ( calculated as Pdet.Qmax + 5Qmax). Regarding treatment we described the need of starting CIC or the presence of complications (urinary tract infections, bladder stones).
A Univariate comparative analysis was performed to compare the characteristics of the patients who needed to start CIC along the follow up versus those who were stable and free of CIC. Binary logistic regression was performed as multivariate analysis to define risk factors for the need to start CIC. All statistical analysis were performed with SPSS®21 (Mac version).

Demographic characteristics
We reviewed  our database with 2496 urodynamic studies between January 2008 and March 2018 and found 172 (6,89%) male patients with urodynamically proven DUA. Mean age was 59,6 years (SD ± 15,1). The majority of patients had voiding symptoms (57 patients (33,1%) or acute urinary retention (29 patients (16,9%)). In 28 patients we found mixed incontinence (16%) or urgency incontinence (26 patients (15,1%)). The ethiology of DUA was neurogenic in 106 patients (61,6%), mainly spinal cord injury (27 patients (25,5%)), multiple sclerosis ( 14 patients (13,2%)) or diabetes mellitus (13 patients (12,3%)). In the other 66 patients (38,4%) the ethiology was non-neurogenic.                         
Urodynamic results
All patients underwent urodynamic study. Near 60% of the patients had another urodynamic diagnosis in the filling phase such as detrusor overactivity (42 patients (24,4%)) or low compliance (17 patients (9,9%)).  Of the 172 patients with DUA, 36 patients (20,9%) were excluded from analysis because CIC was started at the time of the diagnosis. Other 74 (43%) patients were excluded because they continued their follow up in other Hospitals due to geographic reasons. Then, 62 (36,1%) patients were fit for analysis. Table 1 summarizes baseline urodynamic parameters of these patients. No differences were found between neurogenic and non-neurogenic DUA in baseline parameters in the free Uroflowmetry neither in the P/Q study.
Follow up
Mean follow up was 4,88 years (SD + 2,56). Table 2 summarizes the need of CIC and complications during follow-up.
In the non-neurogenic group, there was no significant change in Uroflowmetry variables or in clinical voiding symptoms.
In the neurogenic group, 6 patients who initially were conservatively managed required CIC during follow up due to a worsening in PVR. When reviewing the records of these 6 patients we found in the baseline Urodynamic study, significantly higher PVR (316,66 vs. 114,63 ml p=0,0001) and significantly lower bladder voiding efficiency (9,61 vs. 30,69 % p= 0,017) compared to the other neurogenic patients.
We perform a multivariate analysis to study risk factors for CIC requirement. We included as explicative variables: ethiology (Categorized as neurogenic or non-neurogenic), and baseline urodynamic variables (Qmax, bladder voiding efficiency, Pdet.uo, BCI and PdetQmax). Unfortunately, when performing the logistic binary regression analysis, none of these variables was found as risk factor to require CIC during the follow up.
Regarding complications, there were no differences in UTI or bladder stones between patients according to the DUA ethiology.

Different urodynamic parameters for defining DUA have been explored. In our study we used the 2002 ICS (1) and a BCI <100 as a cut-off point and found a prevalence of 6.89 % in males, similar to other studies (2). Also comparing to other series, the ethiology of DUA is predominantly neurogenic (mainly spinal cord injuries).
Most of papers about DUA focuses on the diagnosis but there are few about follow up and evolution of these patients (3).The Bristol group explored non-neurogenic DUA patients during a long follow-up of more than 10 years. The majority of them remained stable (84%). They didn’t find differences between those who progress compared to those who remained untreated. In our study we explored the need to start CIC including neurogenic DUA patients as we thought it was a paramount treatment change (invasive vs. non-invasive). According to our results, neurogenic DUA patients should be advised that near 20% of them will require to start CIC during the first 5 years of follow up. Conversely, in non-neurogenic DUA patients we can reassure them about the permanence on a medical treatment with low risk of starting CIC.
We search between the urodynamic study variables to establish predictors for the CIC requirements. Unfortunately, this only diagnosis tool that we have to diagnose DUA is unable to detect whose patients with DUA which will evolve to start CIC.

Neurogenic ethiology is the most frequent cause of DUA. Non-neurogenic male DUA patients tend to remain stable and without CIC requirements while near one out of five neurogenic male DUA patients will need to start CIC during their follow up. Unfortunately, none of the parameters obtained at the urodynamic test can predict who will need CIC.

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The natural history of lower urinary tract dysfunction in men: minimum 10-year urodynamic follow-up of untreated detrusor underactivity. Thomas AW, Cannon A, Bartlett E, Ellis-Jones J, Abrams P. BJU Int. 2005;96(9):1295-300.