Grey matter damage is linked to a higher risk of worsening disability, cognitive impairment and death in people with multiple sclerosis (MS), a study suggests.
The damage was more consistently linked to long-term outcomes than damage to white matter, the other main type of brain tissue.
The findings offer new insight into how MRI scans may provide information about potential long-term outcomes.
The researchers wrote: “[Grey matter] damage is consistently associated with clinical outcomes over more than 2 decades.
“These findings highlight the potential relevance of [grey matter]-sensitive MRI metrics for understanding long-term disease evolution.”
Multiple sclerosis is a progressive condition in which inflammation damages the myelin sheath, a protective covering around nerve fibres that helps them send electrical signals.
Most myelin is found in the brain’s white matter. White matter takes its name from the pale colour of myelin.
Because MS damages myelin, it was long considered a condition that mainly affected white matter. However, growing evidence suggests that it also damages grey matter, which contains the bodies of nerve cells.
Although MS symptoms generally worsen over time, the rate of progression can vary considerably between people.
This makes it difficult to predict who will experience faster or slower progression. It has also been unclear whether grey or white matter damage is more useful for predicting long-term outcomes.
Scientists in Italy analysed data from 73 people with relapsing forms of MS who joined an observational study in the 1990s.
Most had been followed for more than 25 years by the time the analysis was carried out.
Researchers used statistical models to examine links between MRI scans taken in the 1990s and health outcomes more than two decades later.
People with greater grey matter damage on their initial scans were significantly more likely to die during the follow-up period.
They were also more likely to experience worsening disability, develop new cognitive problems or progress to more severe forms of MS.
The researchers wrote: “This uniquely long observational period allowed us to investigate whether MRI variables are associated not only with disability worsening and cognitive deterioration but also with MS-related death, arguably the most definitive outcome of disease progression.”
MS is not considered a fatal condition, but it can increase the risk of life-threatening complications such as pneumonia.
Average life expectancy among people with MS is also slightly lower than in the general population.
Grey matter damage had statistically significant links with all the long-term outcomes examined.
White matter damage generally did not show a clear link with long-term clinical outcomes.
The researchers wrote: “[Grey matter] damage was consistently associated with multiple long-term clinical outcomes in relapse-onset MS over a 26-year follow-up.
“These associations were robust across analytical approaches. In contrast, [white matter]-related measures showed less consistent associations.”
The team said the findings support growing evidence that grey matter damage reflects disease processes that continue to influence the accumulation of disability decades later.
