CMT 1A : Differences in potentials + excitability properties in DN simulation

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Clin Neurophysiol. 2005 May;116(5):1153-8.

Differences in potentials and excitability properties in simulated

cases of demyelinating neuropathies. Part I.

Stephanova DI, Daskalova M, androv AS.

Institute of Biophysics, Bulgarian Academy of Sciences, Acad. G.

Bontchev Str. Bl 21, Sofia 1113, Bulgaria.

OBJECTIVE: The aim of this study is to investigate the potentials

(intracellular, extracellular, electrotonic) and excitability

properties (strength-duration and charge-duration curves, strength-

duration time constants, rheobases, recovery cycles) in three cases

of uniform myelin wrap reduction (20, 50 and 70%) along the fibre

length.

METHODS: The internodally systematically demyelinated cases (termed

as ISD1, ISD2 and ISD3) are simulated using our previous double cable

model of human motor fibres.

RESULTS: In the more severely demyelinated cases, the intracellular

potentials are with significantly reduced amplitude, prolonged

duration and slowed conduction velocity, whereas the electrotonic

potentials show greater increase in the early part of the

hyperpolarizing responses. The radial decline of the extracellular

potential amplitudes depends on the radial distance of the field

point and increases with the increase of the distance and

demyelination. The time constants and rheobasic currents increase

with the increase of the degree of demyelination. In the recovery

cycles, the more severely demyelinated cases have greater

refractoriness (the increase in threshold current during the relative

refractory period), supernormality and less late subnormality than

the normal case.

CONCLUSIONS: The myelin thickness has significant effects on the

potentials and axonal excitability properties of the simulated

demyelinated human motor fibres. The obtained abnormalities in the

potentials and excitability properties can be observed in Charcot-

Marie-Tooth disease type 1A (CMT1A).

SIGNIFICANCE: The study provides new information about the

pathophysiology of human demyelinating neuropathies.