Impact of post-contrast MRI in the definition of active multiple sclerosis

Background: For multiple sclerosis (MS) phenotypes classification, the presence of "disease activity" can be defined by clinical relapses and/or by magnetic resonance imaging (MRI) through gadolinium-enhancing (Gd+) lesions or new/enlarged T2 lesions. Recent MRI and pathology findings have demonstrated Gd deposition in the brain, suggesting to avoid Gd administration when dispensable. In this scenario, we aimed to evaluate the contribution of post-contrast MRIs to the definition of "active" MS phenotype. Methods: We retrospectively selected 84 "active" relapsing-remitting MS (RRMS) patients according to Lublin 2013, calculating both the number of Gd+ lesions not detectable as new/unequivocally enlarged on T2 images and the proportion of patients who would be still correctly classified as "active" without Gd administration. Results: 13 out of 164 (7.9%) Gd+ lesions did not correspond to a new/enlarged T2 lesion. Gd administration did not modify the classification of MS as "active" in 83 out of 84 subjects (98.8%). Conclusion: The contribution of Gd+ lesions to the correct classification of RRMS patients as "active" is marginal, thus limiting the need of routine Gd administration for this scope. Further studies are warranted to support these conclusions.