Plasma and cerebrospinal fluid interleukin-6 concentrations in posttraumatic stress disorder

Background: Interleukin-6 (IL-6) secretion is suppressed by glucocorticoids and stimulated by catecholamines. Patients with posttraumatic stress disorder (PTSD) have decreased cortisol and increased catecholamine secretion. The purpose of this study was to assess the relation of IL-6 levels and hypothalamic-pituitary-adrenal and noradrenergic activity in patients with well-characterized PTSD. Methods: Cerebrospinal fluid (CSF) was withdrawn via a lumbar subarachnoid catheter over 6 h from 11 combat veterans with PTSD and 8 age- and sex-matched healthy controls. Blood was withdrawn concurrently. We measured IL-6, CRH and norepinephrine concentrations in the CSF and IL-6, ACTH, cortisol and norepinephrine in plasma. Results: Mean and median CSF IL-6 concentrations were higher in PTSD than in controls (mean = 24.0 vs. 14.6, p = 0.05; median = 26.7 vs. 14.3, p < 0.03): plasma IL-6 concentrations, however, were not different between the two groups. Plasma IL-6 and norepinephrine were positively correlated in the PTSD group (r = +0.74, p < 0.04), but not in normals (r = -0.55, p = 0.20). Conclusions: PTSD patients have increased CSF concentrations of IL-6. Their plasma IL-6 is not elevated but is more tightly associated with noradrenergic output in these patients than in normals. Both findings might be explained by the low cortisol secretion previously reported in PTSD as a result of lowered glucocorticoid suppression of IL-6 secretion. High levels of CSF IL-6 may reflect neurodegeneration or compensatory neuroprotection.