Sensory neuropathy with onion-bulb formation. Report of a case with onset in infancy.

A 27-month-old girl suffered from severe sensory neuropathy with minimal motor dysfunction. The CSF protein level was increased and nerve conduction was severely impaired. Sural nerve biopsy specimen showed increased endoneurial connective tissue. An onion-bulb pattern with concentric interdigitations of Schwann cell cytoplasmic processes and redunbant basal laminae were prominent features under electron microscopy. Degress of myelination in individual fiber was far less than expected. Although the clinical manifestations of onion-bulb neuropathy with onset in infancy have been reported to resemble infantile progressive spinal muscular atrophy, the present case demonstrates that the condition can also appear as severe sensory ataxia.