Interrelation of erectile dysfunction and lower urinary tract symptoms

The association between erectile dysfunction (ED) and lower urinary tract symptoms (LUTS) has garnered attention as investigators have hypothesized a common pathophysiology to explain the assertion that they are causally linked. This relationship between LUTS and ED has received increased attention because both diseases are highly prevalent, frequently co-associate in the same aging male group, and significantly influence the overall quality of life. A causal association between LUTS and ED cannot be established on the basis of the ever-increasing number of epidemiological studies. Attempting to explain a causal relationship between ED and LUTS requires the use of Hill's criterion, which is used by many epidemiologists to separate causal from non-causal explanations. A review of the epidemiological evidence reveals a strong degree of association, internal consistency and dose response effects between ED and LUTS. The temporal relationships between the two remain unknown because of the strong cross-sectional flavor of the epidemiological studies. The issue of an "alternate explanation" to describe the LUTS-ED association appears to be accounted for in that several large studies have provided convincing multiple regression analyses in which the ED-LUTS relationship remains significant. Biologic plausibility is an important issue if the link between ED and LUTS is to have credence. There are four leading theories of how these diseases interrelate. These explanations have a variable amount of supporting data. These include: 1) autonomic hyperactivity effects on LUTS, prostate growth and ED; 2) nitric oxide synthase/nitric oxide levels decreased or altered in the prostate and penile smooth muscle; 3) prostate and penile ischemia; and 4) increased Rho-kinase activation/ endothelin activity. LUTS and sexual dysfunction are highly prevalent in aging men. Both conditions are also significant contributors to overall quality of life. New data has emerged to indicate potential links in epidemiological, physiologic, pathophysiologic and treatment aspects of these two diseases. Using Hill's causality method to separate causal from non-causal explanations linking ED with LUTS, it appears that most epidemiological components are fulfilled.