Subject Review
Myoclonus

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Myoclonus is defined as sudden, brief, shocklike, involuntary movements caused by muscular contractions or inhibitions. Myoclonic movements have now been recognized to have many possible variants and pathophysiologic features. Myoclonus may arise from several sites within the neuraxis, of which the cortex and brain stem reticular formation are the most common. An etiologic classification scheme and electro-diagnostic tests are useful for clinical purposes. Therapy is limited and usually involves symptomatic treatment with valproic acid or clonazepam. Careful attention to the basic characteristics of the movement appearance, the clinical circumstances in which the myoclonus occurs, and the results of the electro-diagnostic assessment techniques provide a basis for identifying the syndrome in which the myoclonus occurs.

Section snippets

Physiologic Characteristics and Clinical Identification of Myoclonus

Identifying the myoclonic jerk is the initial clinical goal. The appearance of the abnormal movement patterns of myoclonus can be appreciated by examining the electromyographic (EMG) discharge patterns. An EMG burst from the wrist flexor muscle group in a normal subject is shown in Figure I A; EMG was performed as quickly and briefly as possible. An EMG burst from the wrist flexor muscle group during myoclonus of the wrist in a patient is shown in Figure 1 B. This myoclonic burst was brief

Clinical Diagnostic Approach to Myoclonus

The best strategy for using the symptom of myoclonus in the diagnosis of its underlying is to view it within the context of the total clinical picture. Information obtained from the history and physical examination is no more important than the characterization of the associated clinical features. Aspects of the patient's history that aid in the diagnosis include history of drug or toxin exposure, history of seizures, past or current medical problems, and family history. Besides delineating the

Evaluation

Diagnostic testing should be considered an extension of the clinical examination. Such testing is usually necessary unless the diagnosis seems straightforward after elicitation of the history and performance of the physical examination. Basic tests (Table 3) should be done in most patients. If, after such testing, the diagnosis is still unknown, advanced testing (Table 3) should be considered. Expert referral may be useful if such detailed testing is indicated. Other testing may include

Treatment Considerations

Classifying the myoclonus and identifying its underlying disorder are especially critical goals relative to treatment considerations. Some causes of myoclonus are easily reversible, such as an acquired abnormal metabolic state, an excisable lesion, or a side effect of a medication. Physiologic myoclonus needs no management other than reassurance. If the myoclonus arises as part of an epileptic syndrome, standard anticonvulsant therapy is used and often includes valproic acid or clonazepam (or

Conclusion

Myoclonus consists of sudden, brief, shocklike, involuntary movements caused by muscular contractions or inhibitions. The cortex and brain stem are the most common origins. The term “myoclonus,” used by itself, is becoming increasingly nonspecific as the different variants are further defined by clinical, genetic, biochemical, and electrophysiologic means. Thus, the clinician must appreciate the differences among the types of myoclonus. A clinical approach based on the four etiologic

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