THE VALUE OF 23NA MRI IN UNDERSTANDING CLINICALLY ISOLATED SYNDROME AND PREDICTING CONVERSION TO MULTIPLE SCLEROSIS – A VOXEL-BASED ANALYSIS

Background: Although a clinically isolated syndrome (CIS) often precedes multiple sclerosis (MS), its precise pathological nature remains elusive. 23Na MRI, probing metabolic function and tissue integrity, may be a valuable tool to identify early pathophysiological alterations in CIS, which may further bear relevance for the disease prognosis. Methods: 32 patients were investigated with 23Na MRI, 1H MRI and clinical measures, including the Symbol Digit Modalities Test and the Expanded Disability Status Scale, within 3 months of their first demyelinating event. Patients were followed over 5 years to monitor their conversion to MS. 13 healthy controls (HC) were also assessed. Tissue sodium concentration (TSC) was measured per voxel and compared between patients and HC, as well as between converting patients and CIS preserved patients, using voxel-based analyses. Voxel-based regression analyses were used to identify associations of TSC with clinical measures and T2 lesion volume in patients. Results: Patients exhibited widespread TSC elevations at 15 local sites within the brain’s normal-appearing white and grey matter, compared to HC. Converting patients, compared to preserved patients, showed lower TSC within 3 local grey matter areas, including the anterior cerebellum, the inferior frontal gyrus and the superior temporal gyrus. Possible explanations are discussed. Clinical measures and T2 lesion volume demonstrated an association with TSC changes in clinically and pathologically relevant brain regions. Conclusion: 23Na MRI has the potential to locate initial metabolic or microstructural pathological alterations in CIS that are also of clinical relevance. It possesses limited value in predicting conversion to MS.