On classification of post-mortem multiple sclerosis plaques for neuroscientists

Plaque classification is proposed based on observation of 348 plaques from 52 post-mortem multiple sclerosis (MS) cases. Four plaque types, ranging from 'earliest lesion' to 'inactive', are described according to immunological activation and degree of demyelination, seen by expression of the Major Histocompatibility Complex (MHC) Class II molecule, HLA-DR, and by Oil Red O staining, respectively. 40% of the plaques were inactive. This result highlights the need for a description of plaque activity for studies of the etiopathogenesis of MS; that is, the earliest and/or the most active plaques should contain the causative agent whereas the burnt out plaques should not.