RIS: new MRI criteria for risk of MS
Individuals with radiologically isolated syndrome (RIS) have incidental magnetic resonance imaging (MRI) abnormalities suggestive of multiple sclerosis (MS).
Recent studies using susceptibility-based imaging have shown that a subgroup of chronic MS white matter lesions (WMLs) have a rim of paramagnetic susceptibility-associated signal loss at the lesion edge, the paramagnetic rim sign (PRS), that is associated with the presence of iron inside phagocytes, which indicates chronic, active demyelination. The objective of this study published at JAMA Neurology was to determine whether patients with RIS have WMLs that are positive for PRS (PRS+).
Twenty-eight adults with RIS were included.
Six hundred thirty WMLs (47%) were included for (presence of the central vein sign (CVS) analysis in accordance with published criteria.
They found that most patients with RIS (17 [61%]) in their cohort had at least 1 PRS+ WML. The number of PRS+ WMLs per patient varied substantially, ranging from 0 to 23. Prior work in MS has shown that such lesions have chronic, active demyelination at the edge and are associated with greater disability.Furthermore, most of the patients with RIS (26 [93%]) also had many CVS+ WMLs meeting the 40% rule , which has been proposed to distinguish MS-associated WMLs from other white matter disorders.
These findings collectively suggest that most WMLs observed in RIS develop from perivenous inflammation and demyelination, and, surprisingly, that most patients with RIS experience chronic, active inflammation.
We found that PRS+ WMLs are correlated with CVS+ WMLs, T1 BHs, WML volume, and brain volume, similar to what has been observed in established MS.
Moreover, there was a correlation between cervical spinal cord (SC) lesion counts and PRS+ WMLs. The presence of an cervical spinal cord (SC) lesion is one of the strongest predictors of developing clinical MS after RIS.
These findings collectively raise the possibility that the PRS may have useful clinical implications regarding prognostication and disease-monitoring in RIS.
This study shows that many patients with RIS have at least 1 and often more WMLs demonstrating PRS, suggesting the presence of subclinical chronic active demyelination, as is often seen in patients with MS with more prominent disability.