Sural nerve biopsy was performed on a six-year-old girl with a slowly progressive distal mixed polyneuropathy. The nerve fiber population was reduced, and of those remaining, approximately half were greatly enlarged, measuring up to 35 microns in cross section. Longitudinal sections showed axonal enlargement to be segmental. Ultrastructurally, swollen axonal segments were filled with neurofilaments in closely-packed swirls which appeared to tie on occasion into granular electron-opaque condensations. Both, myelinated and unmyelinated fibers were involved, and some degree of onion-bulb formation was observed.

Although masses of neurofilaments are found in peripheral axons in other disorders, none approaches the proportions encountered in this unique case.