Resnick et al. first described the urodynamic findings of detrusor overactivity with imparied contraction (DHIC) in elderly patients(1). In our institute  we often experience DHIC in male patients with benign prostatic hyperplasia (BPH) without obvious neurogenic diseases in urodynamic studies. At present, the pathophysiology of DHIC is still unknown, moreover there are scarce reports of DHIC. Therefore, the aim of study is to investigate the relationships between bladder outlet obstruction due to BPH and detrusor overactivity (DO) by comparing urodynamic findings in patients with DO and patients without DO (non-DO) for understanding the pathophysiology of DHIC.

We retrospectively reviewed medical records of male patients with benign prostatic hyperplasia who underwent urodynamic studies (UDS) between 2001 and 2016 in our institute. Patients with apparent neurogenic diseases were excluded in this study. We divided the patients into 2 groups by the existence of DO in the UDS and evaluated urodynamic parameters in each groups. We also divided the patients by the degree of obstruction (Schafer nomogram and ICS nomogram) and projected isovolumetric pressure, and evaluated the urodynamic findings by each group.  Statistical analysis of the data was made with the Mann-Whitney, Chi-square and Spearman test.  P-values less than 0.05 were considered to be significant.

487 patients who underwent UDS were investigated in this study. Mean age was 72.0±7.2 years. (median 72.0 years). 211 of them (43.3%) showed DO, and mean age in DO group and in non-DO group were not significantly different (72.0 years and 71.6 years, respectively)(P=0.0929). Mean maximum cystometric capacity and mean bladder compliance were significantly lower in DO group than in non-DO group (P< 0.0001, respectively) (Table 1). Moreover, detrusor pressure at maximum flow was significantly higher in DO group than in non-DO groups (103.2 cmH2O, 88.6 cmH2O, respectively) (P<0.0001, Table 1). When all patients were divided into 6 groups according to Schafer nomogram, the incidence of DO in each group was increased in proportion to the degree of bladder outlet obstruction (group I:15.8%, group II:41.5%, group III: 44.4%, group IV: 44.6%, group V: 43.7%, group VI: 57.1%) (P=0.05). When all participants were divided into 3 groups by ICS nomogram (unobstructed, equivocal, and obstructed), the incidence of DO significantly correlated with the degree of bladder outlet obstruction (P =0.03), whereas mean ages were not significantly different among 3 groups. The incidence of DO also significantly correlated with projected isovolumetric pressure (P=0.01).

Bladder function during filling was impaired in patients with DO as evidenced by decrease of maximum cystometric capacity and bladder compliance as expected. Interestingly, detrusor contraction during voiding is significantly higher in patients with DO regardless of age. Furthermore, the degree of bladder outlet obstruction has the tendency for the direct proportion to the incidence of DO. In general, bladder contractility is considered to decrease with age in patients with benign prostatic hyperplasia. Therefore, it is assumed that incidence of DO fall in inverse proportion to the degree of bladder outlet obstruction. However, we could not find these findings. Taken together, it is considered that the age deterioration in patients with DO and bladder outlet obstruction is not associated with pathophysiology of DHIC. Other factors might be involved in the pathophysiology of DHIC.

In this retrospective study we found that male patients with DO have significantly higher bladder contractility than patients without DO. Furthermore, the degree of bladder outlet obstruction in male patients correlates with the incidence of detrusor overactivity regardless of age. In conclusion, the impaired bladder contraction in male BPH patients with DO might not be induced by aging but other mechanisms. The pathophysiology of DHIC is further complex and further studies are needed for the treatment of DHIC.

Resnick NM, and Yalla SV:  JAMA 257: 3076–3081, 1987.