Peripheral nerve involvement in familial spastic paraplegia.

A sural nerve biopsy specimen was obtained from a 16-year-old girl affected by a clinically uncomplicated form of familial spastic paraplegia. The electron microscopic study evidenced degenerative changes in some large myelinated fibers. Onion bulb formations and clusters of small myelinated fibers were also observed. Quantitative determinations showed a decreased density of the large myelinated fibers and a mild decrease in the percentage of the endoneural area covered by the myelinated fibers. The unmyelinated fibers were uninvolved except for their participation in onion bulb formations.