New PET-based research published in Lancet Psychiatry found major depressive disorder changes the brain, meaning different treatment may be needed through various stages of the illness.

“To our knowledge, this is the first study to investigate a marker of microglial activation in relation to illness duration and treatment in patients with major depressive disorder,” wrote corresponding author Jeffrey H. Meyer, MD, with the Research Imaging Centre at the Centre for Addiction and Mental Health in Toronto, and colleagues.

The team performed a cross-sectional study of 134 participants, ages 18 to 75 from the Toronto area, with 81 included in the study.

Participants underwent a PET scan of three primary gray-matter regions of the brain and 12 subregions. Scientists used an ⁸F-FEPPA radiotracer to measure levels of specific translocator protein (TSPO)—a marker of inflammation.

Those tested were divided into three groups: 25 patients with 10 or more years of untreated major depressive disorder, 25 with fewer than 10 years of depression and 30 healthy participants.

Results showed TSPO levels were 29 to 33 percent higher in the tested areas of the brain of those with longer, untreated depression compared with those who had shorter durations of the disease without treatment. Similarly, the group with long-term depression had higher TSPO levels compared to the healthy control group.