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Clin Neurophysiol. 2015 Jun;126(6):1246-1254. doi: 10.1016/j.clinph.2014.09.013. Epub 2014 Sep 28.

Abnormal gating of axonal slow potassium current in cramp-fasciculation syndrome.

Author information

1
Department of Neurology, Tokushima University, Tokushima, Japan.
2
Department of Neurology, Tokushima University, Tokushima, Japan. Electronic address: hnodera@tokushima-u.ac.jp.
3
Department of Neurology, Tokushima University, Tokushima, Japan; Department of Neurology, National Hospital Organization Takamatsu Medical Center, Takamatsu, Japan.
4
Department of Neurology, Chiba University, Chiba, Japan.

Abstract

OBJECTIVE:

Cramp-fasciculation syndrome (CFS) is a heterogeneous condition with multiple underlying causes. Although dysfunction of slow K(+) channels has been reported in patients with CFS, testing all potential candidates for this problem using conventional in vitro functional analysis would be prohibitively cost- and labor-intensive. However, relatively economical and non-invasive nerve-excitability testing can identify ion channel dysfunction in vivo when combined with numerical modeling.

METHODS:

Patients with CFS underwent nerve conduction study, needle electromyography, and nerve excitability testing. Mathematical modeling of axonal properties was applied to identify the pathophysiology.

RESULTS:

Four patients had distinct electrophysiological findings (i.e., fasciculation potentials, doublet/multiplet motor unit potentials, and sustained F responses); excitability testing showed the following abnormalities: reduction of accommodation during prolonged depolarization, lack of late sub excitability after a supramaximal stimulation, and reduction of the strength-duration time constant. Mathematical modeling showed a loss of voltage-dependence of a slow K(+) current. None of these patients had a mutation in the KCNQ2, 3, or 5 genes.

CONCLUSIONS:

This study showed that patients with CFS might have abnormal kinetics in a slow K(+) current.

SIGNIFICANCE:

Nerve-excitability testing may aid the decision to start therapeutic intervention such as administration of slow K(+) channel openers.

KEYWORDS:

Axonal excitability; Cramp; Fasciculation; Slow potassium channel

PMID:
25304174
DOI:
10.1016/j.clinph.2014.09.013
[Indexed for MEDLINE]

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