So-called silent brain lesions in patients with early-stage relapsing-remitting multiple sclerosis (RRMS) may, in fact, not be silent at all, according to a French study that linked such lesions to cognitive decline in early MS.
This link has likely been missed since the major tool for measuring disability in MS poorly reflects cognitive function, researchers at Aix-Marseille Université in France argued. This suggests that treatments preventing accumulation of brain lesions may slow the decline in thinking and memory capacity.
The study, “New brain lesions with no impact on physical disability can impact cognition in early multiple sclerosis: A ten-year longitudinal study,” appeared in the journal PLOS ONE.
Although many MS patients clearly experience cognitive decline, even after the first symptomatic episode, research has rarely explored how the loss of cognitive function evolves during early and mid-term disease stages, and if it is linked to brain lesion accumulation.
To address these questions, the French research team enrolled 26 patients who had just experienced their first symptomatic episode. Patients were tested on traditional disability aspects using the Expanded Disability Status Scale (EDSS) and underwent extensive cognitive tests that explored memory, attention, information processing speed and executive functions — cognitive skills that help people get things done. The tests were repeated after one and 10 years.
They also measured the number of brain lesions using T2 magnetic resonance imaging (MRI), which detects both old and new lesions.
After one year, 27 percent of patients showed problems in attention or information processing speed. Another 11.5 percent had abnormal executive functions and an equal percentage had memory problems. At this time, the group had a median EDSS score of only 0.5, with the highest score in the group being 3.
Nine years later, nonetheless, more patients were affected by cognitive problems. While 11.5 percent had been deemed cognitively impaired at year one, the number jumped to 42 percent at year 10.
That increase was, however, not equal among the cognitive domains. Fewer patients had memory problems at year 10, while attention and speed of processing problems were more common.
Meanwhile, the median EDSS score increased to 2.5. Researchers, however, found no links between higher EDSS scores and number of brain lesions. Neither did the brain lesion load correlate with executive function, the area that had deteriorated the most during the study.
When the team, instead, looked at lesions in specific brain areas, another picture emerged. Lesions in the left cerebellum — involved in movement coordination — and the semioval centers, which are both linked to movement and sensory processing, were linked to increasing EDSS scores.
In contrast, lesions in three other brain areas — called the frontal, temporal and parietal lobes — were linked to cognitive problems.
While the researchers concede that their findings must be validated in a larger study, they underscored the importance of preventing the formation of new brain lesions to limit cognitive decline in MS.