Nosology of the leukodystrophies: ultrastructural contributions

Ultrastructural aspects of some of the conditions usually included as "leukodystrophies" are described. In metachromatic leukodystrophy, the most striking ultrastructural features include a variety of inclusions within cells some of which can be identified as oligodendroglia. Some inclusions were relatively amorphous while others possess a well-defined lamellar pattern. The fine structure of the globoid-epithelioid cells of Krabbe's disease differs from that of the usual macrophage and contains membrane-bound areas of relative translucency as well as abundant amorphous moderately osmiophiclic deposits. Epithelioid cells are seen in the perivascular spaces which favors their origin from mesodermal elements and is against their being derived from macroglia. In sudanophilic leukodystrophy there are macrophages which are not distinguishable from macrophages seen in areas of myelin destruction from whatever cause. In the spongy degeneration of infants, there is a peculiar myelin abnormality with splitting of the intraperiod line of the myelin lamellae and the existance of large abnormal mitochondria in astrocyte cytoplasm. There may also be vaculolization of significance within oliogodendroglia cytoplasm. The Rosenthal fibers seen in Alexander's type of leukodystrophy appear as osmiophilic masses in astroyte cytoplasm and probably consist of altered glial filaments.