Histology

In the early stages plaques show marked perivascular cuffing with lymphocytes and some oedema of surrounding tissues. Myelin breakdown products are in the process of being phagocytosed by macrophages and oligodendrocytes are still present; there may even be some proliferation of the latter at the edges of plaques. In the chronic stage there is marked loss of myelin and oligodendrocytes with good preservation of axons. Lymphocytic cuffing is less evident but reactive changes within astrocytes are marked. There is a progressive loss of axons with time. There may be marked atrophy of affected regions which may result in distortion of the shape of the lateral ventricles, producing a variant of hydrocephalus. Chronic lesions may still contain a few lipid-laden macrophages but inflammatory cells are usually sparse.