SuS is an autoimmune disease of the microvasculature in the brain, retina and inner ear. Lesions presumed to be microinfarcts classically involve the CC, but can also be observed in the IC. Although biopsies in Sus are rare, demyelination has been reported. We investigated whether myelin abnormalities could be detected in vivo in SuS using MWI, an advanced MRI technique that provides a quantitative measurement of myelin, termed the myelin water fraction (MWF). The mean MWF reflects the average myelin present within a region of interest (ROI) while the standard deviation (SD) is an indicator of myelin heterogeneity within that ROI.

To assess myelin water imaging (MWI) findings in patients with Susac Syndrome (SuS) and multiple sclerosis (MS) in the corpus callosum (CC) and internal capsules (IC).

MWI data were acquired from 7 Definite or Probable SuS patients following the European Susac Consortium diagnostic criteria, and 7 MS patients following the 2010 McDonald criteria using a gradient and spin echo sequence (GRASE) on a 3T scanner. The MWF of non-lesional tissue in the CC (genu, body, and splenium), and IC was compared between SuS and MS participants

In the CC, MWF was lower in SuS than MS (-20%, p=0.09), and significantly reduced in the body of the CC (-27%, p=0.02), with similar heterogeneity between SuS and MS (p=1.0). In the IC, MWF was significantly higher in SuS compared to MS (+47%, p<0.001) with greater heterogeneity in SuS (+46%, p<0.001).

SuS patients MWF measurements differed regionally from MS patients, who are known to have reduced myelin compared to healthy controls. These findings from seven SuS patients suggest that non-lesional myelin abnormalities may also be a pathologic feature of SuS.