fMRI shows leukoaraiosis may not be harmless after all

Leukoaraiosis, or nonspecific white matter changes, which are comprised of tiny areas in the brain that have been deprived of oxygen and appear as bright white dots on MRI scans, may not be benign and may be a disease that alters brain function in the elderly, according to a study published online Aug. 13 in Radiology.

“There has been a lot of controversy over these commonly identified abnormalities on MRI scans and their clinical impact,” Kirk M. Welker, MD, assistant professor of radiology in the College of Medicine at Mayo Clinic in Rochester, Minn., said in a release. “In the past, leukoaraiosis has been considered a benign part of the aging process, like gray hair and wrinkles.”

Leukoaraiosis lesions are common in the brains of people older than 60 years of age, although the amount of disease varies among individuals.

Welker and colleagues hypothesized that leukoaraiosis alters functional activation during a semantic decision task. To test the hypothesis, the researchers recruited 18 right-handed, cognitively healthy elderly patients with a leukoaraiosis volume of more than 25 cm³ and 18 age-matched controls with a volume of less than 5 cm³.

The patients underwent functional MRI (fMRI) exams as they performed a semantic decision task by identifying word pairs and a visual perception task that involved differentiating straight from diagonal lines.

Although both groups performed the tasks with similar success, the fMRI scans revealed different brain activation patterns between the two groups. Compared with members of the control group, patients with moderate levels of leukoaraiosis had atypical activation patterns, including decreased activation in areas of the brain involved in language processing during the semantic decision task and increased activation in the visual-spatial areas of the brain during the visual perception task.

Although both groups achieved similar semantic decision performance scores, the researchers noted that participants with leukoaraiosis may have employed compensatory measures.

“Different systems of the brain respond differently to disease,” Welker explained. “White matter damage affects connections within the brain’s language network, which leads to an overall reduction in network activity.” 

These differences are important as leukoaraiosis may represent a confounding factor in fMRI scans of elderly patients, including those undergoing brain mapping for surgery or other treatments and for research studies.

“Our results add to a growing body of evidence that this is a disease we need to pay attention to,” he said. “Leukoaraiosis is not a benign manifestation of aging but an important pathologic condition that alters brain function.” Welker et al also suggested preventive measures including risk factor modification to avoid the onset or progression of the condition.