Different effectiveness of tocainide and hydrochlorothiazide in paramyotonia congenita with hyperkalemic episodic paralysis.

We investigated the effectiveness of tocainide and hydrochlorothiazide on muscular symptoms in a patient with paramyotonia congenita and episodic attacks of hyperkalemic paralysis. Generalized weakness was evoked by exercise and potassium loading. Myotonia and weakness were evoked by local muscle cooling. Tocainide prevented myotonia and weakness induced by cooling, but failed to prevent hyperkalemic weakness. Hydrochlorothiazide prevented hyperkalemic weakness, but did not influence symptoms evoked by cooling. These results suggest that, in this disorder, two different mechanisms cause muscular weakness.