Progressive oil-spot-like lesion in multiple sclerosis.

The demyelinating lesion in MS being characterised by an evolutive polymorphism, led to different opinions about the identification of the hypercellularity. The present work deals with data concerning the abundance and the early appearance of macrophages (M) within the lesion, studied with lipid histochemistry methods. The disposition of 3 various types of previously described M, with different lipid content, demonstrates the progressive centrifugal evolution of the recent lesion. At the edge the M are filled exclusively with intensely Baker (phospholipids) stained myelinic granules whereas inside they have a mixed myelinic and sudano-osmiophylic (esterocholesterolic) composition as revealed by Sudan red, Oil rd, Otan and Schultz methods. Surrounding vessels, in the centre of the lesion, M contain exclusively sudano-osmiophylic (esterocholesterolic) granules and crystals. This arrangement of M as to AGE is due to the progressive disintegrative cycle of phagocyted myelin: the youngest at the edge and those undergoing myelin disintegration towards the centre. It is demonstrative for the progressive and centrifugally oil-spot-like extension of the lesion and might explain the round-shape of the small lesions which stop their extension without any morphological correlations.