Definite diagnosis of tMS by histological investigations. Histology shows proliferation of lymphocytes (arrowheads) without atypical features by hematoxylin-eosin (HE) staining (a). Kluver-Barrera staining demonstrates sporadic defects of myelin (arrows), indicating demyelinations (b). Perivascular lymphocyte proliferation is recognized by HE staining (c). These lymphocytes are composed mainly of CD3-positive T-cell lymphocytes (d), and a mixture of CD4-positive (e) and CD8-positive (f) T-cell lymphocytes rules out monoclonal increase of the lymphocytes. The appearance of macrophages (CD68) in the lesion strongly suggests inflammatory disease (g) rather than malignant lymphoma. CD: cluster of differentiation.