We appreciate the insightful comments expressed by Agilli et al regarding our pilot study that proposed that sacral nerve stimulation may decrease urinary nerve growth factor (uNGF) levels in patients with detrusor overactivity. We would like to address their concerns about the study group in which we evaluated uNGF.

Patients in our study were excluded if they had experienced neurologic disease. Although cardiometabolic diseases have been shown to NGF, we chose to use exclusion criteria more specific to the urinary tract system that have been shown to alter uNGF levels in human patients. For this reason, inflammatory conditions such as urinary tract infection and interstitial cystitis were used. Although 15 of our subjects had hypertension and 7 had hyperlipidemia, we believe that further research that will evaluate the effect of cardiometabolic diseases, specifically on uNGF in humans, must be done. Results will help determine precisely which medical comorbidities warrant consideration when patients are being selected for a proper study group in larger future studies.

Our study consisted of 23 cases and 22 control subjects; therefore, 1 case did not have an age-matched control subject. At 88 years old, this patient was an outlier and raised the difference in mean age between the groups. We agree that the mismatched number of cases and control subjects could lead to an unbalanced assessment; however, the patient was included for the purpose of obtaining maximum pilot data. Agilli et al cite that NGF could have been affected by older age. In that study, older age was associated with increased levels of pro-NGF but decreased levels of NGF. In our study, we witnessed the opposite trend in which increased age was associated with elevated levels of NGF. It was also noted that there was a significant difference in body mass index between our cases and control groups. Although Agilli et al cite an article that shows that obesity may cause higher NGF levels, other studies have shown that uNGF is not associated with higher body mass index.

Finally, we appreciate the observation that certain supplements may affect NGF levels. Three patients were receiving vitamin D therapy; 1 patient was receiving oral estrogen/progesterone therapy, and 1 patient was receiving vitamin D, B, and zinc supplementation. To our knowledge, the association of vitamin supplementation affecting uNGF in humans has not been shown. We look forward to performing a larger-powered study that will evaluate uNGF in patients with detrusor overactivity compared with control subjects, at which time comprehensive descriptive characteristics will be analyzed so that independent risk factors for differences in uNGF levels can be determined.