Subtotal aplasia of myelinated nerve fibers in the sural nerve.

Thus far, only very few cases with neuronal maldevelopment in the peripheral nervous system have been reported (Table 1). The present sporadic case manifested itself with peripheral sensorimotor polyneuropathy in early infancy. Clinical findings included pareses and hypaesthesia of distal extremities and severely reduced nerve conduction velocities. During adolescence, cerebellar ataxia developed. Sural nerve biopsy taken at the age of 14.5 years showed severe fascicular hypoplasia, aplasia of large myelinated nerve fibers, and subtotal deficiency of small myelinated nerve fibers without numerical reduction of unmyelinated axons. There was no structural evidence of a progression of myelinated fiber breakdown although some collagen pockets and empty Schwann cell processes among preserved unmyelinated axons indicated some loss of unmyelinated fibers. These findings are interpreted as representing maldevelopment of the myelinated fibers in the peripheral nervous system. Appropriate classification of this unique disease among the known developmental disorders of peripheral nerves is discussed.