1,721,011 research outputs found
Surface-in pathology in multiple sclerosis: a new view on pathogenesis?
No full textWhile multiple sclerosis can affect any part of the CNS, it does not do so evenly. In white matter it has long been recognized that lesions tend to occur around the ventricles, and grey matter lesions mainly accrue in the outermost (subpial) cortex. In cortical grey matter, neuronal loss is greater in the outermost layers. This cortical gradient has been replicated in vivo with magnetization transfer ratio and similar gradients in grey and white matter magnetization transfer ratio are seen around the ventricles, with the most severe abnormalities abutting the ventricular surface. The cause of these gradients remains uncertain, though soluble factors released from meningeal inflammation into the CSF has the most supporting evidence. In this Update, we review this 'surface-in' spatial distribution of multiple sclerosis abnormalities and consider the implications for understanding pathogenic mechanisms and treatments designed to slow or stop them
A longitudinal study of cortical grey matter lesion subtypes in relapse-onset multiple sclerosis
Full text linkBackground: Cortical grey matter (GM) lesions are common in multiple sclerosis (MS), but little is known about their temporal evolution. We investigated this in people with relapsing-remitting (RR) and secondary progressive (SP) MS. Methods: 27 people with RRMS, and 22 with SPMS were included in this study. Phase sensitive inversion recovery (PSIR) scans were acquired on two occasions. Cortical GM lesions were classified as intracortical (IC, only involving GM) and leucocortical (LC, mixed GM-white matter [WM]); WM lesions touching the cortex as juxtacortical (JC). On follow up scans, new IC, LC and JC lesions were identified, and any change in classification of lesions previously observed was noted. WM lesion counts in the whole brain were assessed on PD/T2-weighted scans. Results: Over a mean (SD) of 21.0 (5.8) months, the number of new IC lesions per person per year was greater in SPMS (1.6 [1.9]) than RRMS (0.8 [1.9]) (Mann-Whitney p=0.039). All new LC lesions arose from previously seen IC lesions (SPMS 1.4 [1.8] per person per year, and RRMS 1.1 [1.0]), and none arose de novo or from previously seen JC lesions. Changes in cortical GM (either new IC or IC converting to LC) lesion counts did not correlate with the changes in WM lesion counts. Conclusions: New cortical GM lesions rarely arise from the WM and the rate of new IC lesion formation is not closely linked with WM lesion accrual. IC lesion formation appears to be more common in SPMS than RRMS
Magnetization transfer ratio measures in normal-appearing white matter show periventricular gradient abnormalities in multiple sclerosis
Full text linkIn multiple sclerosis, there is increasing evidence that demyelination, and neuronal damage occurs preferentially in cortical grey matter next to the outer surface of the brain. It has been suggested that this may be due to the effects of pathology outside the brain parenchyma, in particular meningeal inflammation or through cerebrospinal fluid mediated factors. White matter lesions are often located adjacent to the ventricles of the brain, suggesting the possibility of a similar outside-in pathogenesis, but an investigation of the relationship of periventricular normal-appearing white matter abnormalities with distance from the ventricles has not previously been undertaken. The present study investigates this relationship in vivo using quantitative magnetic resonance imaging and compares the abnormalities between secondary progressive and relapsing remitting multiple sclerosis. Forty-three patients with relapsing remitting and 28 with secondary progressive multiple sclerosis, and 38 healthy control subjects were included in this study. T1-weighted volumetric, magnetization transfer and proton density/T2-weighted scans were acquired for all subjects. From the magnetization transfer data, magnetization transfer ratio maps were prepared. White matter tissue masks were derived from SPM8 segmentations of the T1-weighted images. Normal-appearing white matter masks were generated by subtracting white matter lesions identified on the proton density/T2 scan, and a two-voxel perilesional ring, from the SPM8 derived white matter masks. White matter was divided in concentric bands, each ∼1-mm thick, radiating from the ventricles toward the cortex. The first periventricular band was excluded from analysis to mitigate partial volume effects, and normal-appearing white matter and lesion magnetization transfer ratio values were then computed for the 10 bands nearest to the ventricles. Compared with controls, magnetization transfer ratio in the normal-appearing white matter bands was significantly lower in patients with multiple sclerosis. In controls, magnetization transfer ratio was highest in the band adjacent to the ventricles and declined with increasing distance from the ventricles. In the multiple sclerosis groups, relative to controls, reductions in magnetization transfer ratio were greater in the secondary progressive multiple sclerosis compared with relapsing remitting multiple sclerosis group, and these reductions were greatest next to the ventricles and became smaller with distance from them. White matter lesion magnetization transfer ratio reductions were also more apparent adjacent to the ventricle and decreased with distance from the ventricles in both the relapsing remitting and secondary progressive multiple sclerosis groups. These findings suggest that in people with multiple sclerosis, and more so in secondary progressive than relapsing remitting multiple sclerosis, tissue structural abnormalities in normal-appearing white matter and white matter lesions are greatest near the ventricles. This would be consistent with a cerebrospinal fluid or ependymal mediated pathogenesis
A memoir of multiple sclerosis Stephen L Hauser, The Face Laughs While the Brain Cries: The Education of a Doctor, St Martin's Press (2023), p. 304, £24·99, ISBN: 978-1-250-28389-4
Full text link
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Relationship of grey and white matter abnormalities with distance from the surface of the brain in multiple sclerosis
Full text linkOBJECTIVE: To assess the association between proximity to the inner (ventricular and aqueductal) and outer (pial) surfaces of the brain and the distribution of normal appearing white matter (NAWM) and grey matter (GM) abnormalities, and white matter (WM) lesions, in multiple sclerosis (MS).METHODS: 67 people with relapse-onset MS and 30 healthy controls were included in the study. Volumetric T1 images and high-resolution (1 mm(3)) magnetisation transfer ratio (MTR) images were acquired and segmented into 12 bands between the inner and outer surfaces of the brain. The first and last bands were discarded to limit partial volume effects with cerebrospinal fluid. MTR values were computed for all bands in supratentorial NAWM, cerebellar NAWM and brainstem NA tissue, and deep and cortical GM. Band WM lesion volumes were also measured.RESULTS: Proximity to the ventricular surfaces was associated with progressively lower MTR values in the MS group but not in controls in supratentorial and cerebellar NAWM, brainstem NA and in deep and cortical GM. The density of WM lesions was associated with proximity to the ventricles only in the supratentorial compartment, and no link was found with distance from the pial surfaces.CONCLUSIONS: In MS, MTR abnormalities in NAWM and GM are related to distance from the inner and outer surfaces of the brain, and this suggests that there is a common factor underlying their spatial distribution. A similar pattern was not found for WM lesions, raising the possibility that different factors promote their formation.</p
- …
