Paramagnetic rim lesion formation is predicted by the initial gadolinium-enhancing lesion diameter

Paramagnetic rim lesions (PRLs) are a magnetic resonance imaging (MRI) marker of compartmentalized intraparenchymal inflammation.

The primary objective was to investigate clinical, demographic, and MRI factors that may be predictive of the future formation of PRL.

This is a retrospective analysis of longitudinal data. Patients were included if they had ⩾1 gadolinium-enhancing lesion on any historical MRI and follow-up scan(s) ⩾6 months afterward on a standardized 3T MRI using the filtered phase component of a susceptibility-sensitive sequence ("SWAN"). Regression and machine-learning models were used to identify the predictive ability of demographic, clinical, immunological, treatment-related, and MRI predictors of PRL formation.

A total of 64 patients having 229 contrast-enhancing lesions (CELs) were included. Among all predictors, the diameter of the initial enhancing lesion was the most influential for determining subsequent PRL formation; every millimeter increase in diameter increased the risk of PRL formation by 44%. Other factors did not contribute additional information; the administration of steroids was not associated with any effect.

The long-axis diameter of a CEL is the best translational predictor of subsequent PRL formation at follow-up. This measure holds promise as a method to identify patients at high risk of chronic active lesion formation during the acute inflammatory window.