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CHICAGO -- People who had SARS-CoV-2 infection showed brain changes on diffusion microstructure imaging (DMI), cross-sectional data suggested.

Widespread microstructural alterations were seen in people with long COVID neurologic symptoms and in people who had COVID but recovered, reported Alexander Rau, MD, of the University Hospital Freiburg in Germany, at the annual meeting of the Radiological Society of North America.

"We did see a signature in the brain microstructure that is associated with COVID-19 infection, but the pattern is different among those people with long COVID-19 and those who do not have long COVID-19," Rau said.

Conventional MRI showed no brain volume loss in these patients. "While comparing their structural or conventional brain scans, we did not find any lesion or alteration that could explain the severe symptoms in patients with post-COVID syndrome," Rau pointed out.

How SARS-CoV-2 may affect the brain is largely unknown. In 2022, a longitudinal study of U.K. Biobank participants showed that mild SARS-CoV-2 infection was associated with brain volume loss and structural changes on MRI. More recently, reported that diffusion MRI showed damaged white matter in people previously hospitalized for COVID with persistent post-COVID symptoms.

Rau and colleagues assessed 89 people with neurologic long COVID symptoms (mean age 49 years, 57% female), 46 people who recovered from COVID (mean 42 years, 66% female), and 38 people who never had SARS-CoV-2 infection (mean 42 years, 50% female). To look for possible alterations, the researchers used DMI, a technique that allows the brain's microstructure to be approximated using a diffusion weighted imaging sequence. Participants were scanned in 2020.

Long COVID was defined by as new or continued symptoms 3 months after initial SARS-CoV-2 infection, with these symptoms lasting at least 2 months.

Participants with long COVID were recruited from the hospital's post-COVID clinic. Cognitive performance was measured with the Montreal Cognitive Assessment (). Olfactory disturbance was tested with , and fatigue level was assessed with the Würzburger Fatigue Inventory for Multiple Sclerosis ().

The researchers found distinct brain networks that correlated with long COVID symptoms, after adjusting for age and sex. Altered brain microstructure in the mesiotemporal cortex was associated with cognitive dysfunction. Patients who had problems with their sense of smell had microstructural changes in the olfactory cortex, while those with fatigue had altered microstructure in the brain stem, including the ascending arousal network.

"We can see there is an altered microstructure that is associated with COVID-19 infection, and when we take our findings along with data from other sources, we see that this is compatible with accelerated aging, rather than with neurodegeneration," Rau said. "However, this is most speculative. To make this conclusive, we need a lot more research."

Confounding factors may have influenced the outcomes in this cross-sectional study, observed neuroradiologist Max Wintermark, MD, of the University of Texas MD Anderson Cancer Center in Houston, who wasn't involved with the research.

"The study is limited in generalization by the lack of a longitudinal perspective," Wintermark told MedPage Today. "We would really want to know if the longitudinal imaging changes parallel evolution of symptoms over time."

Rau said the next step is to perform longitudinal scans to see whether alterations persist and uncover prognostic factors that may identify who will recover from long COVID.

"We also need to corroborate the information from the scans with other bio data, such as obtained from blood draws, to gain a more profound insight in being able to predict which patients will have a post COVID-19 condition," he added.

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