Myoclonus: A Pragmatic Approach
Positive myoclonus is usually easy to recognise as a rapid, simple, brief movement of a limb or limbs, often with an identifiable trigger. This must be distinguished from other involuntary movements such as tics, tremor (figure 2), dystonia and psychogenic movement disorders (Table 1). In complex cases, the bedside classification of abnormal movements may not be possible. Neurophysiology should then help, for example, EEG, multi-channel EMG (with or without time-locked EEG and back-averaging; figure 2) and magnetoencephalography.
(Enlarge Image)
Figure 2.
Multi-channel EMG of (A) cortical myoclonus affecting the arm from a contralateral frontal glioma. Note the synchronised activity in agonist and antagonist muscles. (B) Lower limb tremor leading to rhythmic, alternating activation of agonist and antagonist muscles. Note these features do not distinguish myoclonus from tremor (Meinck 2007).
Negative myoclonus – a sudden brief loss of tone – is harder to recognise and must be actively sought, watching the patients holding out their arms. Negative myoclonus is an important cause of unexplained falls in the older subjects (bouncing gait).
Is It Myoclonus?
Positive myoclonus is usually easy to recognise as a rapid, simple, brief movement of a limb or limbs, often with an identifiable trigger. This must be distinguished from other involuntary movements such as tics, tremor (figure 2), dystonia and psychogenic movement disorders (Table 1). In complex cases, the bedside classification of abnormal movements may not be possible. Neurophysiology should then help, for example, EEG, multi-channel EMG (with or without time-locked EEG and back-averaging; figure 2) and magnetoencephalography.
(Enlarge Image)
Figure 2.
Multi-channel EMG of (A) cortical myoclonus affecting the arm from a contralateral frontal glioma. Note the synchronised activity in agonist and antagonist muscles. (B) Lower limb tremor leading to rhythmic, alternating activation of agonist and antagonist muscles. Note these features do not distinguish myoclonus from tremor (Meinck 2007).
Negative myoclonus – a sudden brief loss of tone – is harder to recognise and must be actively sought, watching the patients holding out their arms. Negative myoclonus is an important cause of unexplained falls in the older subjects (bouncing gait).
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