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Paramyotonia congenita: Abnormal short exercise test, and improvement after mexiletine therapy
Author(s) -
Jackson Carlayne E.,
Barohn Richard J.,
Ptacek Louis J.
Publication year - 1994
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/mus.880170710
Subject(s) - mexiletine , medicine , weakness , missense mutation , compound muscle action potential , stimulation , endocrinology , muscle weakness , cardiology , anesthesia , surgery , chemistry , electrophysiology , mutation , biochemistry , gene
The diagnosis of paramyotonia congenita (PC) can be aided by demonstrating a decrease in compound motor action potential amplitude after exercise and a decrement on repetitive stimulation, following cold exposure. We report a patient with PC who presented with complaints of cold‐induced hand and jaw stiffening, in the absence of any episodes of weakness. Treatment with mexiletine led to resolution of the abnormalities exhibited during a short exercise test and repetitive stimulation following ice bath immersion. Molecular genetic analysis revealed a missense mutation (cytosine to thymidine) on chromosome 17 in the alpha‐subunit of the skeletal muscle sodium channel gene that results in the replacement of threonine with methionine. This case demonstrates that, despite the absence of weakness, the short exercise test following cold exposure can be used to confirm the diagnosis of PC in patients without episodic weakness. Furthermore, improvement of the electrophysiologic abnormalities with mexiletine was documented, corresponding with clinical improvement. © 1994 John Wiley & Sons, Inc.