People with long-COVID exhibit patterns of changes in the brain that are different from fully recovered COVID-19 patients, according to research.

The results based on diffusion microstructure imaging (DMI), a novel MRI technique, showed no brain volume loss or any other lesions that might explain the symptoms of long COVID.

However, COVID infection induced a specific pattern of microstructural changes in various brain regions, and this pattern differed between those who had long COVID and those who did not.

"To the best of our knowledge, this is the first study comparing patients with long COVID to both a group without a history of COVID-19 and a group that went through a COVID-19 infection but is subjectively unimpaired," said Alexander Rau, from the Department of Neuroradiology and Diagnostic and Interventional Radiology at University Hospital Freiburg in Freiburg, Germany.

"This study allows for an in vivo insight into the impact of COVID-19 on the brain.

"Here, we noted grey matter alterations in both patients with long-COVID and those unimpaired after a COVID-19 infection. Interestingly, we not only noted widespread microstructural alterations in patients with long COVID but also in those unimpaired after having contracted COVID-19," Rau said.

The findings also revealed a correlation between microstructural changes and symptom-specific brain networks associated with impaired cognition, sense of smell and fatigue.

"Expression of post-COVID symptoms was associated with specific affected cerebral networks, suggesting a pathophysiological basis of this syndrome," Rau said.

For the study, the team compared MRI brain scans of three groups: 89 patients with long-term COVID, 38 patients who had contracted COVID-19 but did not report any subjective long-term symptoms, and 46 healthy controls with no history of COVID-19.

The researchers first compared the cerebral macrostructure of these three groups to test for atrophy or any other abnormalities. Next, they used DMI to gain a deeper insight into the brain.

DMI looks at the movement of water molecules in tissues. By studying how water molecules move in different directions and at various speeds, DMI can provide detailed information on the microstructure of the brain. It can detect even very small changes in the brain, not detectable with conventional MRI.

The study will be presented next week at the annual meeting of the Radiological Society of North America (RSNA) in Chicago.