With reference to the paper by Gratzke et al  , we would like to comment on the definition of nocturia.
The current definitions of nocturia (the complaint that the person has to awaken at night one time or more to void) and nocturnal polyuria (when an increased proportion of the 24-h output occurs at night) prove to be of limited utility in managing patients with lower urinary tract symptoms (LUTS). Pharmacologic treatment of LUTS due to benign prostatic hyperplasia (BPH) results in limited improvement of nocturia. A good example comes from the CombAT study, in which combination therapy provided −0.5 improvement in International Prostate Symptom Score question 7, which may be considered statistically significant but also clinically irrelevant  . In the only trial specifically investigating the effectiveness of BPH surgery on nocturia, an average change of one episode per night was observed (from 2.4 to 1.4 awakenings per night)  . In our daily practice, it is difficult to understand which patient will experience significant improvement of nocturia using the current definition. Some patients will continue to produce an amount of urine that is larger than their bladder capacity, and that cannot be influenced by pharmacologic or surgical treatments of LUTS due to benign prostatic enlargement (BPE).
Looking at renal and bladder physiology, we propose a new definition of nocturia and nocturnal polyuria. We suggest that nocturia and nocturnal polyuria can be defined by volume of the nocturnal urine output, which is lower than the patient bladder capacity in the first case and larger in the second. Using this definition, one might assume that no BPH surgery will be able to reduce nocturnal polyuria, whereas one could expect that patients suffering from nocturia could benefit from treatment of BPH (to be proven in future trials).
Following our working hypothesis, a number of research question can be identified. What is the prevalence of nocturia and nocturnal polyuria (according to this new definition) in male and female populations? What is the effectiveness of pharmacologic and surgical treatment of LUTS due to BPE or benign prostatic obstruction on nocturia? What are the conditions underlying nocturnal polyuria? What is the effectiveness of treatments for different underlying conditions with regard to nocturnal polyuria?
We believe that the new definitions we propose will stimulate discussion among the experts and, hopefully, help advance research in this area.