In a first-of-its-kind study, researchers have found signs of inflammation within the neurocircuitry associated with adult obsessive-compulsive disorder (OCD). The findings were reported June 21 in JAMA Psychiatry.

Until now, only a small percentage of OCD cases have been linked to inflammation, occurring in a part of the brain called the basal ganglia -- potentially as the result of childhood infection. Sophia Attwells, HBSc of the Center for Addiction and Mental Health in Toronto, Canada and colleagues now use recent advances in positron emission tomography or PET scanning to identify inflammation in multiple parts of the brain involved in OCD.

Attwells’ co-authors on the study include Elaine Setiawan, Ph.D., a 2013 Young Investigator; Romina Mizrahi, M.D., Ph.D., FRCP, a 2014 Independent Investigator and 2010 Young Investigator; and Jeffrey Meyer, M.D., Ph.D., FRCP, a 2015 Distinguished Investigator and 2000 and 1998 Young Investigator, all from the Center for Addiction and Mental Health.

The study included PET scans from 20 healthy people and 20 patients with diagnosed OCD. The scans were used to identify and measure the density of translocator protein (TSPO). Levels of this protein increase when neuroinflammatory cells called microglia are activated. The researchers found increases in TSPO volume, ranging from 23.5 -35.6 percent elevation, in multiple brain areas of OCD patients compared to healthy people.

Dr. Meyer and colleagues also noted that scores on a scale used to measure OCD distress corresponded significantly with TSPO volume measurements in a part of the brain called the orbitofrontal cortex.

The study was small and cannot itself prove a causal connection between inflammation and adult OCD. Nevertheless, “to our knowledge,” the authors write, “this study is the strongest evidence to date for inflammation in the brain in OCD.” They suggest that their findings may be useful in developing pharmaceutical treatments for OCD, perhaps even by repurposing other drugs already used to treat neuroinflammation in conditions such as Alzheimer’s disease.