Plasma levels of brain-derived neurotrophic factor and interleukin-6 in patients with dysthymic disorder: comparison with age- and sex-matched major depressed patients and healthy controls

In the present study, we investigated the serum BDNF levels and plasma IL-6 levels in patients with dysthymic disorder, major depressive disorder and control subjects. Eighteen patients who met the DSM-IV criteria (American Psychiatric Association, 1994) for dysthymic disorder (male/female: 5/13; age: 36 ± 9 year) and 20 patients (male/female: 7/13; age: 38 ± 10 year) who met the criteria for major depressive disorder were enrolled. The serum BDNF levels in patients with dysthymic and major depressive disorder were significantly lower than those in the control subjects. However, no difference was found between the dysthymic group and major depression group. The plasma IL-6 levels in the dysthymic group and major depression group were significantly higher than those in the control group. No difference was observed in the plasma IL-6 levels between the dysthymic group and major depression group. These results suggest that the pathophysiology of dysthymic disorder and major depression might be similar in terms of the blood levels of BDNF and IL-6.