Excitability of motor and sensory axons in multifocal motor neuropathy |
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Affiliation: | 1. Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore;2. NeuroCure Clinical Research Center, Charité University Medicine, Berlin, Germany;3. Clinical and Experimental Multiple Sclerosis Research Center, Department of Neurology, Charité University Medicine, Berlin, Germany;4. Division of Neurology, Department of Medicine, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia;5. Department of Neurology, National Neuroscience Institute, Singapore;6. Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore |
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Abstract: | ObjectiveTo assess excitability differences between motor and sensory axons of affected nerves in patients with multifocal motor neuropathy (MMN).MethodsWe performed motor and sensory excitability tests in affected median nerves of 20 MMN patients and in 20 age-matched normal subjects. CMAPs were recorded from the thenar and SNAPs from the 3rd digit. Clinical tests included assessment of muscle strength, two-point discrimination and joint position.ResultsAll MMN patients had weakness of the thenar muscle and normal sensory tests. Motor excitability testing in MMN showed an increased threshold for a 50% CMAP, increased rheobase, decreased stimulus-response slope, fanning-out of threshold electrotonus, decreased resting I/V slope, shortened refractory period, and more pronounced superexcitability. Sensory excitability testing in MMN revealed decreased accommodation half-time and S2-accommodation and less pronounced subexcitability. Mathematical modeling indicated increased Barrett-Barrett conductance for motor fibers and increase in internodal fast potassium conductance for sensory fibers.ConclusionsExcitability findings in MMN suggest myelin sheath or paranodal seal involvement in motor fibers and, possibly, paranodal detachment in sensory fibers.SignificanceExcitability properties of affected nerves in MMN differ between motor and sensory nerve fibers. |
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Keywords: | Multifocal motor neuropathy Excitability Sensory axons Motor axons Ion channels Schwann cell CMAP" },{" #name" :" keyword" ," $" :{" id" :" k0040" }," $$" :[{" #name" :" text" ," _" :" compound muscle action potential DML" },{" #name" :" keyword" ," $" :{" id" :" k0050" }," $$" :[{" #name" :" text" ," _" :" distal motor latency GM1" },{" #name" :" keyword" ," $" :{" id" :" k0060" }," $$" :[{" #name" :" text" ," _" :" ganglioside HCN" },{" #name" :" keyword" ," $" :{" id" :" k0070" }," $$" :[{" #name" :" text" ," _" :" hyperpolarization-activated cyclic nucleotide-gated channels I/V" },{" #name" :" keyword" ," $" :{" id" :" k0080" }," $$" :[{" #name" :" text" ," _" :" current–voltage relation MMN" },{" #name" :" keyword" ," $" :{" id" :" k0090" }," $$" :[{" #name" :" text" ," _" :" multifocal motor neuropathy Qt" },{" #name" :" keyword" ," $" :{" id" :" k0100" }," $$" :[{" #name" :" text" ," _" :" charge duration RMSE" },{" #name" :" keyword" ," $" :{" id" :" k0110" }," $$" :[{" #name" :" text" ," _" :" root mean square error S2-accommodation" },{" #name" :" keyword" ," $" :{" id" :" k0120" }," $$" :[{" #name" :" text" ," _" :" second slow component of the accommodation to depolarization SNAP" },{" #name" :" keyword" ," $" :{" id" :" k0130" }," $$" :[{" #name" :" text" ," _" :" sensory nerve action potential SR" },{" #name" :" keyword" ," $" :{" id" :" k0140" }," $$" :[{" #name" :" text" ," _" :" stimulus–response TEd90-100" },{" #name" :" keyword" ," $" :{" id" :" k0150" }," $$" :[{" #name" :" text" ," _" :" depolarizing threshold electrotonus at 90–100 ms TEh90-100" },{" #name" :" keyword" ," $" :{" id" :" k0160" }," $$" :[{" #name" :" text" ," _" :" hyperpolarizing threshold electrotonus at 90–100 ms |
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