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cIMPACT-NOW (the Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy) was established to evaluate and make practical recommendations on recent advances in the field of CNS tumor classification, particularly in light of the rapid progress in molecular insights into these neoplasms. For Round 2 of its deliberations, cIMPACT-NOW Working Committee 3 was reconstituted and convened in Utrecht, The Netherlands, for a meeting designed to review putative new CNS tumor types in advance of any future World Health Organization meeting on CNS tumor classification. In preparatory activities for the meeting and at the actual meeting, a list of possible entities was assembled and each type and subtype debated. Working Committee 3 recommended that a substantial number of newly recognized types and subtypes should be considered for inclusion in future CNS tumor classifications. In addition, the group endorsed a number of principles-relating to classification categories, approaches to classification, nomenclature, and grading-that the group hopes will also inform the future classification of CNS neoplasms.

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Conformation-sensitive antibodies against myelin oligodendrocyte glycoprotein (MOG) are detectable in patients with optic neuritis, myelitis, opticomyelitis, acute or multiphasic disseminated encephalomyelitis (ADEM/MDEM) and brainstem/cerebral cortical encephalitis, but are rarely detected in patients with prototypic multiple sclerosis. So far, there has been no systematic study on the pathological relationship between demyelinating lesions and cellular/humoral immunity in MOG antibody-associated disease. Furthermore, it is unclear whether the pathomechanisms of MOG antibody-mediated demyelination are similar to the demyelination patterns of multiple sclerosis, neuromyelitis optica spectrum disorders (NMOSD) with AQP4 antibody, or ADEM. In this study, we immunohistochemically analysed biopsied brain tissues from 11 patients with MOG antibody-associated disease and other inflammatory demyelinating diseases. Patient median onset age was 29 years (range 9–64), and the median interval from attack to biopsy was 1 month (range 0.5–96). The clinical diagnoses were ADEM (n = 2), MDEM (n = 1), multiple brain lesions without encephalopathy (n = 3), leukoencephalopathy (n = 3) and cortical encephalitis (n = 2). All these cases had multiple/extensive lesions on MRI and were oligoclonal IgG band-negative. Most demyelinating lesions in 10 of 11 cases showed a perivenous demyelinating pattern previously reported in ADEM (153/167 lesions) and a fusion pattern (11/167 lesions) mainly in the cortico-medullary junctions and white matter, and only three lesions in two cases showed confluent demyelinated plaques. In addition, 60 of 167 demyelinating lesions (mainly in the early phase) showed MOG-dominant myelin loss, but relatively preserved oligodendrocytes, which were distinct from those of AQP4 antibody-positive NMOSD exhibiting myelin-associated glycoprotein-dominant oligodendrogliopathy. In MOG antibody-associated diseases, MOG-laden macrophages were found in the perivascular spaces and demyelinating lesions, and infiltrated cells were abundant surrounding multiple blood vessels in and around the demyelinating lesions, mainly consisting of macrophages (CD68; 1814 ± 1188 cells/mm2), B cells (CD20; 468 ± 817 cells/mm2), and T cells (CD3; 2286 ± 1951 cells/mm2), with CD4-dominance (CD4+ versus CD8+; 1281 ± 1196 cells/mm2 versus 851 ± 762 cells/mm2, P < 0.01). Humoral immunity, evidenced by perivascular deposits of activated complements and immunoglobulins, was occasionally observed in some MOG antibody-associated demyelinating lesions, and the frequency was much lower than that in AQP4 antibody-positive NMOSD. Subpial lesions with perivenous demyelination were observed in both ADEM and cortical encephalitis. Our study suggests that ADEM-like perivenous inflammatory demyelination with MOG-dominant myelin loss is a characteristic finding of MOG antibody-associated disease regardless of whether the diagnostic criteria of ADEM are met. These pathological features are clearly different from those of multiple sclerosis and AQP4 antibody-positive NMOSD, suggesting an independent autoimmune demyelinating disease entity.

The presence of tau-positive glial inclusions has been recently found a consistent feature in the brains of patients with progressive supranuclear palsy (PSP), corticobasal degeneration (CBD) and Pick's disease (PiD). These inclusions are classified based on cellular origin as tau-positive astrocytes, presumably either fibrillary or protoplasmic, coiled bodies and glial threads. Immunohistochemically, their major structural component is abnormal tau proteins, similar to those found in Alzheimer's disease. Nevertheless, their morphology, including ultrastructural profile, has been suggested to be distinctive for each disease. The profile and extent of particular glial inclusions correlate well with disease phenotype. Highly characteristic correlations include tufts of abnormal fibers in PSP, astrocytic plaques and dense glial threads in CBD and ramified astrocytes and small Pick body-like inclusions in PiD. The significance of the inclusions in disease pathogenesis and their biochemical characteristics remain to be clarified. Nevertheless, these distinctive glial lesions most likely reflect fundamental alterations in isoform composition of tau as well as its specific cellular and regional expression in sporadic tauopathies.