Emergence of thalamic magnetization transfer ratio abnormality in early relapsing-remitting multiple sclerosis

While there is now evidence for thalamic abnormality in established secondary progressive and relapsing-remitting multiple sclerosis (MS), it remains unclear when such abnormality begins. This study investigated the emergence of thalamic abnormality in relapsing-remitting MS by assessing the thalamic magnetization transfer ratio (MTR) in a cohort with clinically early disease. Twenty-three patients with early relapsing-remitting MS (mean age 37; mean disease duration 1.9 years; Expanded Disability Status Scale (EDSS) range 0-3) and 19 healthy controls (mean age 34) were imaged yearly with a magnetization transfer imaging sequence. Twenty-two MS patients and 14 controls completed two-year follow-up. Regions of interest were placed in both thalami and mean thalamic MTR calculated. At baseline, significant differences between patient and control thalamic MTR were not observed. However, at years one and two, the thalamic MTR in patients was significantly lower than control MTR. Although baseline lesion volume did not correlate with baseline thalamic MTR, at year one, an association between baseline lesion volume and year one thalamic MTR emerged. There was also a significant inverse correlation between EDSS and thalamic MTR (r = -0.47, P = 0.02). The study suggests that thalamic involvement occurs within the first five years of MS onset, when most patients are still minimally disabled.