Myelin splitting in the spongy lesion in Leigh encephalopathy.

A spongy lesion consists of numerous vacuoles, mainly in the central gray matter, and is a characteristic finding in subacute necrotizing encephalopathy (Leigh encephalopathy); the cause of this lesion is unknown. An ultrastructural study on the vacuolated lesions in the left putamen of a patient with subacute necrotizing encephalopathy due to a deficiency of mitochondrial enzyme complexes I and IV revealed that the vacuoles were formed through the splitting of myelin. Because myelin splitting is commonly caused by toxic or metabolic diseases in humans and experimental animals, we believe that the vacuolation was due to the splitting of myelin which was caused by abnormal mitochondrial metabolism, even though this lesion is most commonly found in the white matter. We do not know whether the spongy lesion is formed only through myelin splitting in patients with subacute necrotizing encephalopathy; however, myelin splitting must play an important role in the formation of the spongy lesion.