Remyelinated lesions in multiple sclerosis: magnetic resonance image appearance

BACKGROUND: Various types of pathologic mechanisms in multiple sclerosis (MS) can alter magnetic resonance imaging (MRI) signals, and the appearance of remyelinated lesions on MRI is largely unknown. OBJECTIVE: To describe the MRI appearance of remyelinated lesions in MS. DESIGN: Comparison of postmortem MRI findings with histopathologic findings. SETTING: Brain donations from a general community.Patients Magnetic resonance images from 36 rapid autopsies yielded 161 areas that could be matched with histologic characteristics, including 149 focal T2-weighted abnormalities, with a range of signal intensities on T1-weighted images. In a subset of 49 lesions, magnetization transfer ratio could be determined. MAIN OUTCOME MEASURES: An observer blinded to the MRI findings assessed the presence of remyelination using light microscopic criteria; in 25 areas, in situ hybridization was used to assess the presence of oligodendrocytes expressing proteolipid protein messenger RNA. RESULTS: Remyelinated areas were found in 67 lesions (42%): partial remyelination was present in 30 lesions (19%), whereas 37 lesions (23%) were fully remyelinated. Remyelinated lesions contained enhanced numbers of oligodendrocytes containing proteolipid protein messenger RNA. All areas with remyelination shown histopathologically were hyperintense on T2-weighted images. Strong hypointensity on T1-weighted images was significantly associated (chi2 = 29.8, P<.001) with demyelinated and partially remyelinated lesions compared with fully remyelinated lesions. The magnetization transfer ratio of remyelinated lesions (mean [SD], 27.6% [41%]) differed (F = 46.3, P<.001) from both normal-appearing white matter (35.2% [32%]) and demyelinated lesions (22.3% [48%]). CONCLUSIONS: Remyelinated lesions return an abnormal signal on T2-weighted images. Both T1-weighted images and magnetization transfer ratio may have (limited) additional value in separating lesions with and without remyelination.