Ultrastructure of a Cerebral White Matter Lesion in a 41-Year-Old Man With Leigh’s Encephalomyelopathy (LEM)

A brain biopsy taken from a 41-year-old man with Leigh’s encephalomyelopathy (LEM) was studied under the electron microscope. The sample of cerebral white matter revealed degenerated oligodendrocytes, reactive astrocytes and scavenger cells filled with miscellaneous debris. Myelin underwent splitting and vacuole formation as well as lamellar and vesicular dissolution. Degenerative and reactive changes were prominent in the axons, many of which were calcified. There was marked fibrous gliosis of the tissue and the extracellular space was enlarged. The small vessels were notably involved; evidence of capillary growth was also found. In sum, the overall picture was one of loss of tissue continuity, loss of axons and loss of myelin, opposite to which stood expansion of the extracellular space, accumulation of filament-filled astroglial process, hypertrophy and hyperplasia of the capillaries and increase of the tissue cellularity. The study has confirmed and defined at the ultrastructural level the well-known histological features of LEM. However, the formal, let alone the causal pathogenesis of the disease remains as obscure as ever.