Treatment resistance in major depression is correlated with increased plasma levels of neurofilament light protein reflecting axonal damage.

Treatment resistant major depression is accompanied with a sizable impact on quality of life with severe consequences for social integrity, individual health and socioeconomic state. In- and outpatient care of patients with treatment resistant major depression remains very challenging for both patients and the health system. One reason is the limited knowledge on the etiology of treatment resistance in major depression resulting difficulties developing efficient treatment strategies for this group of severe depressed patients. Therefore, new focuses on research are needed. Biomarkers reliably reflecting neuropathological processes could help to understand the actual mechanisms in treatment resistance. Neurofilament light protein might be a reliable biomarker of axonal damage in the brain. Due to accumulating evidence that major depression is associated with axonal damage, it is our hypothesis that treatment resistant major depression is correlated with persistent axonal damage within circuits processing affective responses. Axonal damage is reflected by increased levels of neurofilament light protein in plasma. To evaluate our hypothesis, neurofilament light protein will be measured in a group of patients with homogeneous symptomatology of treatment resistant major depression.