Influence of depression symptoms on serum tumor necrosis factor-alpha of patients with chronic low back pain

Introduction: Patients with chronic low back pain (cLBP) have high rates of comorbid psychiatric disorders, mainly depression. Recent evidence suggests that depressive symptoms and pain, as interacting factors, have an effect on the circulating levels of inflammatory markers relevant to coronary artery disease. Our previous work showed a higher serum level of an inflammatory marker tumour necrosis factor-alpha (TNF alpha) in patients with cLBP, which did not correlate with intensity of low back pain alone. In the present study we investigated the cross-sectional associations of depressive symptoms, low back pain and their interaction with circulating levels of TNF alpha. Methods: Each group of 29 patients with cLBP alone or with both cLBP and depression was age-matched and sex-matched with 29 healthy controls. All subjects underwent a blood draw for the assessment of serum TNF alpha and completed a standardised questionnaire regarding medication, depression scores according to the German version of Centre for Epidemiological Studies Depression Scale (CES-D), pain intensity from a visual analogue scale, and back function using the Roland and Morris questionnaire. The correlations between TNF alpha level and these clinical parameters were analysed. Results: There were no differences in TNF alpha level between cLBP patients with and without depression. Both cLBP patients with (median = 2.51 pg/ml, P = 0.002) and without (median = 2.58 pg/ml, P = 0.004) depression showed significantly higher TNF alpha serum levels than healthy controls (median = 0 pg/ml). The pain intensity reported by both patient groups was similar, while the patients with depression had higher CES-D scores (P < 0.001) and worse back function (P < 0.001). The variance analysis showed that the interaction between TNF alpha level and pain intensity, CES-D scores, sex, body mass index and medication was statistically significant. Conclusions: Depression as a comorbidity to cLBP did not influence the serum TNF alpha level. It seems that TNF alpha somehow acts as a mediator in both cLBP and depression, involving similar mechanisms that will be interesting to follow in further studies.