Disease relevance of Myokymia

• A potassium-channel gene (KCNA1) has been found to be responsible for one of its subgroups, familial periodic cerebellar ataxia with myokymia (FPCA/+M; MIM 160120) [1].
• Identification of two new KCNA1 mutations in episodic ataxia/myokymia families [2].
• The frequency of several clinical signs such as myoclonus, dystonia and myokymia increased with the number of CAG repeats whereas the frequency of others was related to disease duration [3].
• Clinicians use many terms including undulating myokymia, neuromyotonia, Isaacs' syndrome and Cramp-Fasciculation Syndrome to describe the motor manifestations of generalized peripheral nerve hyperexcitability (PNH) [4].
• The unusual clinical features of CMTD were associated with fasciculation, cramps, myokymia, impaired muscular relaxation and percussion myotonia with their electromyographic (EMG) correspondent, responsive to valproic acid (VPA) therapy [5].

High impact information on Myokymia

• Mutation analysis of the KCNA1 coding region in these families identified four different missense point mutations present in the heterozygous state, indicating that EA/myokymia can result from mutations in this gene [6].
• One type of EA is characterized by brief episodes of ataxia with myokymia (rippling of muscles) evident between attacks [6].
• Linkage studies in four such families suggested localization of an EA/myokymia gene near the voltage gated K+ channel gene, KCNA1 (Kv1.1), on chromosome 12p [6].
• Myokymia, unusual side-effect of clofibrate [7].
• We propose that a difference in firing patterns between motoneurons and central neurons, combined with the drastically slowed voltage activation of the R207W mutant, explains why this particular KCNQ2 mutant causes myokymia in addition to BFNC [8].

Chemical compound and disease context of Myokymia

• Two patients developed a Guillain-Barre-like syndrome and a third suffered neuropathy and myokymia during therapy with sodium aurothiomalate [9].
• Myokymia decreased when ionized Ca++ was increased after IV infusion of CaCl2 [10].
• Hereditary myokymia and paroxysmal ataxia linked to chromosome 12 is responsive to acetazolamide [11].
• Discussion is presented on the possible mechanism by which anticonvulsant and steroid therapy exert their effects on myokymia [12].
• After an epidural nerve block with 1 per cent lidocaine 10 ml, the myokymia temporally improved, during which time the hyperexcitable F-waves became normalized [13].

Biological context of Myokymia

• Axonal action potential conduction was altered as well in the sciatic nerve--a deficit potentially related to the pathophysiology of episodic ataxia/myokymia, a disease associated with missense mutations of the human K(V)1.1 gene [14].
• Affected members in Family B (KCNA1 C731A) exhibit myokymia alone, suggesting a new phenotype of isolated myokymia [15].

Gene context of Myokymia

• The diminished activity of mutant KCNQ2 channels accounts for neonatal epilepsy and myokymia; the cellular locus of these effects may be axonal initial segments and nodes [16].
• Myokymia and neonatal epilepsy caused by a mutation in the voltage sensor of the KCNQ2 K+ channel [8].
• Similarly, the clinical spectrum associated with potassium channel, KQT-like mutations was extended to include the channelopathy myokymia and neonatal epilepsy [17].
• Morvan's fibrillary chorea: a paraneoplastic manifestation of thymoma [18].
• Depressor septi nasi myokymia [19].

Analytical, diagnostic and therapeutic context of Myokymia

• Increasing ionized Ca++ (by intravenous infusion of CaCl2) decreased the myokymia [20].

References