Twitch response in a myopathy with impaired relaxation but no myotonia

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Abstract
A patient with slow muscle relaxation but without accompanying motor unit or myotonic electrical activity had a unique staircase twitch response to repeated nerve stimulation. During 1‐Hz stimulation, twitches recorded by measurement of the ankle dorsiflexor group displayed progressively increasing relaxation times with successive stimuli (37% increase) unlike the progressively decreasing relaxation time of the normal response (12–37% decrease). The response may be diagnostic of this unusual myopathy; the test methods are noninvasive and easily tolerated.