In a case-control study of 40 patients who were treated at a tertiary care psychiatric hospital in Canada, the level of translocator protein total distribution volume (TSPO VT), a marker of gliosis, was 9.23 mL/cm3 among patients with COVID-DC and 7.72 mL/cm3 among control persons. Differences were particularly notable in the ventral striatum and dorsal putamen.
“Most theories assume there is inflammation in the brain [with] long COVID,” but that assumption had not been studied, author Jeffrey H. Meyer, MD, PhD, Canada Research Chair in Neurochemistry of Major Depressive Disorder at the University of Toronto, said in an interview. “Such information is pivotal to developing treatments.”
The study was published online in JAMA Psychiatry.
Quantifiable marker
The investigators sought to determine whether levels of TSPO VT, which are quantifiable with PET, are elevated in the dorsal putamen, ventral striatum, prefrontal cortex, anterior cingulate cortex, and hippocampus of patients with COVID-DC, compared with patients without this syndrome. These brain regions were chosen, according to the authors, “because injury in these regions, which can cause gliosis, also induces symptoms of COVID-DC.”
The study was conducted from April 2021 through June 30, 2022. The investigators compared levels of TSPO VT in the selected brain regions of 20 participants with COVID-DC (mean age, 32.7 years; 60% women) with that of 20 control persons (mean age, 33.3 years; 55% women). TSPO VT was measured with fluorine F18–labeled N-(2-(2-fluoroethoxy)benzyl)-N-(4-phenoxypyridin-3-yl)acetamide PET.
The difference in TSPO VT was most noticeable in the ventral striatum (mean difference, 1.97 mL/cm3) and dorsal putamen (mean difference, 1.70 mL/cm3). The study authors suggest that gliosis in these areas may explain some of the persistent symptoms reported in structured clinical interviews and assessed on neuropsychological and psychological testing.
For patients with COVID-DC, motor speed on the finger-tapping test was negatively associated with dorsal putamen TSPO VT (r, −0.53). The 10 participants with COVID-DC whose speed was lowest had higher mean dorsal putamen TSPO VT levels than those of control persons by 2.3 mL/cm3.
The investigators could not assess a possible association between the ventral striatum TSPO VT and anhedonia because all participants had these symptoms. No significant correlations were found between depression and TSPO VT in the prefrontal cortex or anterior cingulate cortex.
The authors acknowledged that the study was cross-sectional, and so the duration of persistently elevated TSPO VT is not yet known. In addition, elevation in TSPO VT is not completely specific to glial cells, and although correlations with finger-tapping test performance reflect associations between brain changes and symptoms, they do not prove cause and effect.
“Presently, clinicians can use treatments for symptoms in other illnesses that are [also] common with long COVID. We need better than this,” said Dr. Meyer. “Clients with long COVID should be able to state their symptoms, and the practitioner should have an evidence-based matching treatment to recommend.”
Research is ongoing. “We are acquiring more information regarding different types of inflammation in the brain, whether there is ongoing injury, and whether treatments that influence inflammation are helpful,” said Dr. Meyer.