Paramyotonia congenita: abnormal short exercise test, and improvement after mexiletine therapy

CE Jackson, RJ Barohn… - Muscle & Nerve: Official …, 1994 - Wiley Online Library
CE Jackson, RJ Barohn, LJ Ptacek
Muscle & Nerve: Official Journal of the American Association of …, 1994Wiley Online Library
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 …
Abstract
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.
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