Axonal excitability in primary amyloidotic neuropathy

Abstract

Introduction: Acquired and hereditary amyloidosis can cause peripheral neuropathy, but the mechanisms by which this occurs have not been established. Threshold tracking techniques allow in vivo assessment of the properties of the axonal membrane and may shed light on pathogenetic mechanisms underlying neuropathic disorders.

Methods: We studied 10 subjects with primary amyloidosis using conventional nerve conduction studies and quantitative sensory, autonomic, and axonal excitability testing of median motor and sensory fibers.

Results: As expected, subjects with amyloidosis had evidence of small- and large-fiber neuropathy on conventional testing. There was no significant difference in axonal excitability between subjects and controls apart from the stimulus required to activate sensory fibers.

Conclusions: Amyloid-related neuropathy does not produce a change in membrane potential as either a primary or secondary event. This suggests that ischemia and axonal compression are unlikely mechanisms for the neuropathy.

Keywords: amyloidosis; autonomic testing; axonal excitability; peripheral neuropathy; quantitative sensory testing.