Strength-duration properties of sensory and motor axons in alcoholic polyneuropathy.

OBJECTIVE: The strength-duration time constant (SDTC) is a measure of axonal excitability and depends on the biophysical properties of the axonal membrane. The strength-duration time constant can provide information about Na+ channel function. We aimed to examine changes in the SDTCs of motor and sensory fibers in the median nerves in patients with alcoholic polyneuropathy.

METHODS AND RESULTS: We measured the SDTCs of motor and sensory fibers in 17 patients with alcoholic polyneuropathy (15 men and two women) after stimulating the right median nerve at the wrist. The results were compared with ten healthy age-matched subjects (six men and four women). In patients, the SDTC and rheobase for the motor fibers were 370.8+/-97.4 micros and 3.9+/-1.7 mA; for the sensory fibers, the SDTC and rheobase were 464.7+/-104.3 micros and 3.3+/-1.9 mA. In controls, the SDTC and rheobase for the motor fibers were 359.3+/-103.5 micros and 3.5+/-1.9 mA; for the sensory fibers, the SDTC and rheobase were 478.9+/-113.9 micros and 2.1+/-1.5 mA. Sensory fibers had significantly longer SDTCs and lower rheobase than motor fibers in patients and controls. However, when the values of the patients and controls were compared, a statistically significant difference was only found for the rheobase of sensory fibers (p=0.037).

CONCLUSIONS: Although alcoholic neuropathy corresponds to the pattern of axonopathy, it did not act on the SDTC of the median nerve, which depends on the biophysical properties of the axonal membrane at the node of Ranvier. The process causing axonal degeneration in alcoholic neuropathy may affect internodal channels other than nodal channels or the Na+ -K+ ATP pump.