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Myoclonus: a pragmatic approach
  1. Dora Lozsadi
  1. Correspondence to Dora Lozsadi, Department of Neurosciences, St George's Hospital, Blackshaw Rd, London SW17 0QT, UK; lozsadi{at}doctors.org.uk

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Abstract

Myoclonus is a brief (less than half a second) contraction involving agonist and antagonist muscles, leading to a sudden jerk. It may be a normal phenomenon, as in the so-called ‘sleep starts’. When pathological, myoclonus is a symptom of a broad range of neurological and systemic diseases. Alternatively, it may signal non-organic illness (8% of myoclonus is psychogenic). This review provides pragmatic and systematic guidance to the assessment and differential diagnosis of adult patients presenting with myoclonus.

Introduction

We have all experienced physiological myoclonus in the form of hiccups, sneezes or sleep starts (hypnic jerks). Myoclonus may sometimes be generated by a normal brain under toxic or metabolic stress.1 Pathological myoclonus may occur in many neurological diseases, such as epilepsy, dementia or movement disorder. Subtle jerks may pass unrecognised, for example, teenagers with juvenile myoclonic epilepsy may describe themselves as ‘clumsy’ due to jerks in the morning. Myoclonus in the older people may be misdiagnosed as unexplained falls or a ‘bouncing gait’ (figure 1).

Figure 1

Proximal lower limb myoclonus (presumed subcortical) leading to loss of balance and falls (image downloaded from internet).

Myoclonus is transient in a quarter of cases, responding to treatment of the underlying cause. However, its successful management depends on correctly diagnosing the aetiology.

With such a wide range of causes, the clinical assessment of pathological myoclonus in adults requires a systematic approach. This review aims to facilitate its management through describing an approach to the clinical review, differential diagnosis and optimal treatment of patients with myoclonus.

Definition

Myoclonus (or electric chorea) is a sudden, brief (most often <100 ms), jerky, shock-like involuntary movement. It may be positive or negative. When positive, the cause is the contraction of a single (or a group) agonist and antagonist muscles. When negative, there is transient (<500 ms) interruption of tonic muscle …

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