Response to ‘Increase of nerve growth factor levels in the human herniated intervertebral disc: can annular rupture trigger discogenic back pain?’ – authors’ reply

Excerpt

We appreciate the interest and attention paid by Agilli and Ekinci, and we agree with their point that nerve growth factor (NGF) levels could be affected by multiple factors [1]. As pointed out, the paper would be improved by considering the effects of these factors; thus the data were re-examined. This analysis found that the number of patients who had neuropsychiatric diseases and use medications (one patient in the herniated group and two patients in the nonherniated group) and had diabetes mellitus (two patients in each group) were similar between the two groups. As Bullo and colleagues described, obesity is one of the important factors affecting NGF levels in blood samples [2]. These authors also indicated the influence of body mass index (BMI) on NGF levels; thus, the BMI of our patients was analyzed and included in the multivariate analysis. The BMI of the two groups showed no significant difference (24.0 ± 4.0 in the herniated group and 25.3 ± 3.2 in the nonherniated group, P = 0.20), and Pearson’s correlation analysis showed no significant correlation between the level of NGF and BMI (P = 0.91). The multivariate analysis adjusted for age, sex, disc degeneration and BMI still showed a significant correlation between disc herniation and NGF levels (P = 0.018). …