Initial brain and spine MRI (A-H) and pathologic findings of corpus callosum biopsy (I-L). (A-D) Initial brain MRI showed markedly increased extent of multifocal patchy and confluent T2/fluid-attenuated inversion recovery hyperintense lesions with heterogeneous enhancement at the right parietal lobe and corpus callosum. (E, F) Spine MRI showed multiple T2 hyperintense lesions (C6-7 and T1 segments, arrowheads) with nodular enhancement (arrows). (G, H) Multiple eccentric short-segment thoracic spinal lesions (T4-T5/6, T6/7 and T9-10 segments, arrowheads) with multifocal enhancing lesions (arrows) were also observed. (I) Infiltration of some cytotoxic T-lymphocytes was observed, especially in a perivascular cuffing pattern, on frozen section (Hematoxylin and Eosin [H&E] staining, ×100). (J) Lymphocytes were stained with CD8 immunohistochemical stain (×200). (K) Most parenchyma was filled with many foamy macrophages and some lymphocytes (H&E, ×200). (L) Staining for myelin basic protein (MBP), suggesting myelin phagocytosis, is patchy within the lesion, indicative of diffuse demyelination (MBP immunohistochemical stain, ×100).