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  • Updated 11.27.2023
  • Released 04.07.1994
  • Expires For CME 11.27.2026




Myoclonus, characterized by involuntary, abrupt muscle contractions followed by relaxation, presents a complex clinical landscape. This article offers a comprehensive overview of myoclonus, focusing on differential diagnosis, etiology, and therapeutic strategies. Myoclonus manifests across a spectrum of diseases and conditions, necessitating a systematic diagnostic approach. Understanding the clinical context surrounding myoclonus is paramount. The initial step involves categorizing myoclonus based on its clinical features, followed by additional testing as needed. Physiological classification augments diagnostic insights. Once the diagnosis is established, interventions targeting the underlying cause or providing symptomatic relief become crucial. In this update, we organize the treatment of myoclonus according to its pathophysiology, incorporating recent advancements, including the potential use of deep brain stimulation or botulinum toxin injection for management.

Key points

• Myoclonus can be a symptom or a sign, but it is not a diagnosis.

• Myoclonus occurs in numerous diseases and conditions, necessitating an organized approach to diagnostic evaluation.

• Classification based on examination findings, clinical circumstances, and pathophysiology offers complimentary, not redundant, information.

• A symptomatic treatment approach is best strategized based on the physiology classification of the myoclonus.

• There should be a thorough search for myoclonus etiology and consideration for etiology treatment before symptomatic treatment is considered.

Historical note and terminology

Myoclonus was initially described as "paramyoklonus multiplex" by Friedreich in 1881 when he observed it in a patient with myoclonus. The term "myo" was employed to differentiate these rapid movements from epileptic disorders, "para" indicated their symmetry, and "multiplex" underscored the multifocal nature of the condition. It was not until 1986 that Lowenfeld proposed a shortened version, simply "myoklonus" (70). In 1899, Rabot contributed to the field by delineating nonprogressive familial myoclonic epilepsy. Subsequently, in 1903, Lundborg classified myoclonus into three distinct groups: essential, symptomatic, and familial myoclonic epilepsy.

Etymologically, "myoclonus" itself signifies "a quick movement of muscle." Clinically, myoclonus encompasses sudden, brief, shock-like involuntary muscle movements, which can result from muscular contractions (positive myoclonus) or inhibitions (negative myoclonus). These manifestations usually originate within the central nervous system (31; 28).

The classification of myoclonus can be approached from various angles, including clinical presentation, etiology, examination findings, or physiological characteristics. When considering clinical presentation, four primary categories are employed: physiologic, essential, epileptic, or symptomatic myoclonus. Each of these categories encompasses a range of underlying causes and clinical scenarios.

On examination, myoclonus may exhibit rhythmic characteristics, which some movement disorder specialists may refer to as "tremor," or it may more commonly present as arrhythmic. Stimulus-sensitive myoclonus is denoted as "reflex myoclonus," whereas action-sensitive myoclonus is described as "action (or intention) myoclonus."

Myoclonus can also be classified based on its distribution within the body: focal or segmental (confined to a specific region), multifocal (involving various body parts, not necessarily simultaneously), or generalized (affecting an entire body part in a single jerk).

Furthermore, the physiological classification considers the type and location of electrical discharge, resulting in categories such as cortical, cortical-subcortical, subcortical-nonsegmental, segmental, or peripheral myoclonus.

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