[Pathology and definition of multiple sclerosis]

Still today, as for the time of Charcot, multiple sclerosis is defined by pathology with the presence of inflammatory demyelinating foci ("plaques") disseminated in the white matter of the central nervous system (CNS). Each lesion follows its genuine course with an acute formation followed by a more or less complete regression whereas new lesions are forming elsewhere in the CNS throughout the disease duration. A permanent dynamics of the inflammatory activity, substratum of the lesional "dissemination in space and time" characteristic of the disease, is therefore operating. During the relapsing-remitting phase, focal lesions are at the forefront of the pathological abnormalities. During the progressive phase, be it secondary or primary, macroscopic atrophy and axonal loss, the main explanation of the irreversible neurological disability and the expression of the diffuse, chronic and progressive degeneration of the CNS, are emerging to the first place. Persisting controversies are many. Are there several distinct immunohistopathological patterns of the disease or do they correspond to different moments of the same disease? Is there a continuum between classic MS and pathological variants such as Marburg's disease, Balo's concentric sclerosis, Schilder's disease, and Devic's acute neuromyelitis optica or are there distinct nosological entities? As for autoimmunisation which leads to the selective destruction of myelin, is it primary or secondary to an oligodendrocytic apoptotic process?