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Neuromyotonia
  1. Paul Maddison
  1. Department of Neurology, Royal Victoria Infirmary, Newcastle upon Tyne, UK; Email: paul{at}piglet2.demon.co.uk

    Abstract

    INTRODUCTION

    Neuromyotonia is a very rare condition of spontaneous, continuous muscle activity of peripheral nerve origin. It is characterized clinically by muscle twitching at rest (visible myokymia), cramps that can be triggered by voluntary or induced muscle contraction, and impaired muscle relaxation (pseudomyotonia). Often, patients also have symptoms of excessive sweating and more rarely mild muscular weakness, and paraesthesia Following the electrophysiological account in Denny-Brown & Foley 1948 of ‘undulating myokymia’, the first full description of the syndrome of ‘continuous musclefibre activity’ was made by Isaacs (1961). He established the peripheral nerve origin of the spontaneously-occurring discharges by noting the persistence of abnormal EMG activity after proximal nerve block, no change in spontaneous muscle activity during general anaesthesia with thiopentone, and that the depolarizing muscle relaxant succinylcholine and neuromuscular blocking agent curare both produce electrical silence after a few minutes.

    PATHOPHYSIOLOGY

    Neuromyotonia can sometimes be seen in isolation, or as

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