Myoclonus: Symptoms, Types, Causes and Treatment

Myoclonus is a movement disorder characterized by sudden, brief, involuntary muscle jerks. These rapid muscle contractions or inhibitions can occur in healthy individuals, but when persistent or severe, they may signal an underlying neurological or systemic condition. This article explores the key aspects of myoclonus—including symptoms, types, causes, and treatment options—drawing on the latest clinical research and expert consensus.

Symptoms of Myoclonus

Myoclonus presents with a range of symptoms that can vary widely depending on the underlying cause, anatomical origin, and affected muscle groups. Recognizing these symptoms is crucial for early diagnosis and effective management.

Symptom	Description	Commonality	Source
Muscle Jerks	Sudden, brief, shock-like movements	Universal	3 6 11
Negative Jerks	Sudden pauses or interruptions in ongoing muscle activity	Often present	6 8
Distribution	Focal, multifocal, segmental, or generalized	Varies by type	9 11
Triggers	Action, posture, sensory stimuli, emotions, fatigue	Frequent	2 5 6
Associated Issues	Gait disturbance, ataxia, dystonia, cognitive or psychiatric symptoms	Variable	1 2 5 12

Table 1: Key Symptoms

Understanding Myoclonus Symptoms

Myoclonus is defined by its hallmark symptom: a rapid, involuntary jerk of one or more muscles. These jerks are typically very brief—lasting milliseconds—and may be caused by either sudden muscle contraction (positive myoclonus) or inhibition (negative myoclonus) 6 8 11.

Types of Jerks

• Positive Myoclonus: Sudden muscle contraction (e.g., a quick, upward jerk).
• Negative Myoclonus: Sudden loss of muscle tone, causing a brief lapse (e.g., dropping an object unexpectedly) 6 8.
• Rhythmic or Irregular: Jerks can occur in a rhythmic fashion, be periodic, or appear irregularly 8.

Distribution and Context

• Focal: Affecting a single area, such as the face or hand.
• Segmental: Involving adjacent body parts, like the neck and shoulder.
• Multifocal or Generalized: Multiple, non-contiguous areas or the entire body 9 11.
• Triggers: Jerks may be provoked by movement (action myoclonus), maintaining a posture, sudden noise, light, stress, or emotions 2 5 6.

Associated Features

Myoclonus can occur with other symptoms, including:

• Ataxia: Unsteady gait or coordination problems 1 2.
• Dystonia: Sustained or intermittent muscle contractions causing abnormal postures 5 12.
• Cognitive or Psychiatric Symptoms: Especially in neurodegenerative or genetic disorders 1 5 12.
• Functional Symptoms: Some cases may have a psychological or functional origin, with abrupt onset and variable presentation 9.

Recognizing these symptoms and their context is the first step towards accurate diagnosis and management.

Types of Myoclonus

The classification of myoclonus is essential for understanding its prognosis and guiding treatment. Myoclonus is categorized in several ways: by clinical context, anatomical origin, and pathophysiology.

Type	Defining Features	Typical Presentation	Source
Physiological	Occurs in healthy people (e.g., sleep starts)	Benign, transient	11
Essential	Isolated myoclonus with no other neurological signs	Focal or multifocal	11
Epileptic	Associated with epileptic seizures	Generalized or focal	6 11
Symptomatic	Due to identifiable condition (e.g., neurodegenerative, metabolic, drug-induced)	Varies	1 3 4 5 11
Cortical	Originates in motor cortex	Action-induced, facial/hand affected	6 9 11
Subcortical	Originates below cortex (basal ganglia, brainstem)	Generalized or segmental	3 6 9 11
Spinal	Originates in spinal cord	Segmental or propriospinal	6 9
Peripheral	Originates in peripheral nerves	Rare, focal	6 9
Functional	Psychogenic or functional movement disorder	Variable, often abrupt	9

Table 2: Myoclonus Types

Classifying Myoclonus

Clinical Context

• Physiological Myoclonus: Common in healthy individuals, such as hiccups or sleep starts (hypnic jerks). These are benign and do not indicate disease 11.
• Essential Myoclonus: Isolated, often hereditary, with no other neurological symptoms. May remain stable or progress slowly 11.
• Epileptic Myoclonus: Occurs as part of epilepsy syndromes (e.g., juvenile myoclonic epilepsy, progressive myoclonic epilepsies). Jerks are typically generalized and can be disabling 2 6 11.
• Symptomatic Myoclonus: Secondary to an identifiable cause, which may include neurodegenerative diseases (e.g., Niemann-Pick type C, Creutzfeldt-Jakob disease), metabolic disorders, drug reactions, or structural lesions 1 3 4 5 8 11.

Anatomical/Pathophysiological Classification

• Cortical Myoclonus: Most common, often action-induced, affecting hands and face. Linked to abnormal cortical excitability 6 9 11.
• Subcortical Myoclonus: Involves deeper brain structures (basal ganglia, thalamus, brainstem). May cause generalized, segmental, or multifocal jerks 6 9 11.
• Spinal Myoclonus: Originates in the spinal cord, seen as segmental or propriospinal myoclonus—jerks travel along the spinal axis 6 9.
• Peripheral Myoclonus: Very rare, associated with nerve irritation or injury 6 9.
• Functional (Psychogenic) Myoclonus: Often abrupt, variable, and inconsistent. May have preceding emotional or psychological stressors 9.

Special Types

• Orthostatic Myoclonus: Occurs in the legs when standing, seen in elderly or those with gait disorders 4.
• Myoclonus-Dystonia Syndrome: Involves both myoclonus and dystonia, often genetic (SGCE, KCTD17 mutations) 5 12 14 15.

Understanding the type of myoclonus helps tailor diagnostic workup and treatment.

Causes of Myoclonus

Myoclonus is a symptom, not a disease itself, and arises from a broad spectrum of causes—ranging from benign to serious, acute to chronic, and genetic to acquired.

Cause Category	Examples	Notable Features	Source
Genetic	SGCE/KCTD17 mutations, PME, storage diseases	Early onset, familial	1 2 5 12 14
Neurodegenerative	CJD, Parkinson’s, Niemann-Pick C	Progressive, often severe	1 4 8
Epileptic	Juvenile myoclonic epilepsy, PME	Generalized, seizures	2 6 8
Metabolic/Toxic	Renal/hepatic failure, hypoxia, drug reactions	Acute or subacute onset	3 6 11
Drug-induced	Quetiapine, other medications	Reversible if recognized	3 4 6
Structural Lesions	Tumors, stroke, trauma	Focal or segmental	6 11
Functional	Psychogenic factors	Variable, non-organic	9
Unknown	No clear cause in some patients	"Idiopathic"	9 11

Table 3: Major Causes of Myoclonus

Exploring the Causes

Genetic Causes

• Hereditary Myoclonus: Mutations in the SGCE gene (myoclonus-dystonia), KCTD17, and genes involved in progressive myoclonic epilepsies (e.g., GOSR2 in North Sea PME) are well-documented 2 5 12 14.
  • Features: Childhood or adolescent onset, family history, often associated with dystonia or ataxia.
  • Inheritance: SGCE mutations are often paternally inherited due to maternal imprinting 5 14.
• Storage Diseases: Niemann-Pick type C and other lysosomal storage disorders can present with myoclonus, ataxia, and cognitive decline 1.

Neurodegenerative and Epileptic Causes

• Neurodegenerative Disorders: Creutzfeldt-Jakob disease (CJD), Parkinson's disease, and related disorders may show prominent myoclonus, sometimes as an early sign 1 4 8.
• Epileptic Syndromes: Juvenile myoclonic epilepsy and progressive myoclonic epilepsies present with both myoclonus and seizures 2 6 8.

Acquired Causes

• Metabolic/Toxic: Acute or chronic metabolic derangements (renal or hepatic failure, hypoxia, electrolyte imbalances) can trigger myoclonus. Correction of the underlying issue may resolve symptoms 3 6 11.
• Drug-induced: Certain drugs (antipsychotics like quetiapine, opioids, antidepressants) can induce myoclonus, often dose-dependent and reversible upon stopping the medication 3 4 6.

Structural and Functional Causes

• Structural Lesions: Tumors, strokes, or trauma affecting the cortex, basal ganglia, or spinal cord can cause focal or segmental myoclonus 6 11.
• Functional (Psychogenic): Functional myoclonus, previously called "psychogenic," is thought to have psychological origins and often presents atypically 9.

Unexplained/Idiopathic

Despite advances in genetic and metabolic testing, in some patients the cause remains elusive 9 11 13.

Treatment of Myoclonus

Effective management of myoclonus requires a personalized approach, starting with identification and treatment of any underlying cause. When this is not possible, symptomatic therapies can help reduce disability, though responses vary.

Treatment	Indication/Type	Key Points	Source
Treat Underlying Cause	Metabolic, drug-induced, structural	First priority, may resolve myoclonus	3 6 11 16 17
Antiepileptics	Cortical/epileptic myoclonus	Levetiracetam, valproic acid, piracetam effective	6 7 16 17
Clonazepam	Various types	Useful for subcortical, spinal, segmental, functional	6 7 16 17
Botulinum toxin	Focal/segmental myoclonus	Variable success	6 7 17
Polytherapy	Refractory cases	Multiple drugs often required	6 7 16
Deep Brain Stimulation (DBS)	Myoclonus-dystonia, refractory cases	GPi or VIM targets; improves symptoms	15 17
Physical/psychotherapy	Functional myoclonus	Multidisciplinary, includes psychotropics	17

Table 4: Treatment Approaches

Approaching Treatment

Underlying Cause

• Address Reversible Factors: Always look for and treat reversible causes—correct metabolic derangements, discontinue offending drugs, treat infections or structural lesions 3 6 11 16 17.

Symptomatic Pharmacologic Therapy

• Cortical/Epileptic Myoclonus: Levetiracetam is first-line, with valproic acid and clonazepam as alternatives. Piracetam is also used, especially in Europe 6 7 16 17.
  • Caution: Phenytoin and carbamazepine may worsen myoclonus and should be avoided in cortical types 17.
• Subcortical/Brainstem Myoclonus: Clonazepam is the mainstay; levetiracetam and valproate may be considered 6 7 16 17.
• Spinal Myoclonus: Typically less responsive to antiepileptics, but clonazepam and baclofen may help. Botulinum toxin is useful for focal cases 6 7 17.
• Polytherapy: Most patients need a combination of drugs for optimal control 6 7 16.

Non-Pharmacologic and Advanced Therapies

• Botulinum Toxin: For focal or segmental myoclonus, especially when not responsive to oral drugs 6 7 17.
• Deep Brain Stimulation (DBS): Reserved for severe, treatment-resistant cases, especially myoclonus-dystonia; targeting the globus pallidus internus (GPi) or ventral intermediate nucleus (VIM) of the thalamus can yield significant improvements 15 17.
• Physical and Psychotherapy: Essential for functional myoclonus, often requiring a multidisciplinary approach with neurologists, psychiatrists, and therapists 17.

Limitations and Challenges

• Limited Evidence: Most treatments are based on small case series or expert opinion; randomized controlled trials are rare 7 10 16.
• Side Effects: Sedation, cognitive impairment, and other adverse effects may limit therapy 6 7 16.
• Tailored Approach Needed: Treatment must be individualized based on myoclonus type, severity, and patient factors 7 11 16.

Conclusion

Myoclonus is a complex and diverse movement disorder that can range from benign, physiological phenomena to disabling symptoms of serious neurological disease. Understanding its symptoms, classification, underlying causes, and treatment options is critical for optimal patient care.

Key Points:

• Myoclonus is defined by sudden, brief, involuntary muscle jerks that may be positive or negative in nature.
• Symptoms vary widely in distribution, triggers, and associated features (e.g., ataxia, dystonia, cognitive or psychiatric issues).
• Classification by clinical context and anatomical origin is essential for diagnosis and management.
• Causes include genetic mutations, neurodegenerative diseases, epileptic syndromes, metabolic or toxic insults, medications, structural lesions, and functional (psychogenic) factors.
• Treatment focuses first on addressing reversible causes, then on symptomatic management using antiepileptics, clonazepam, botulinum toxin, and, in selected cases, deep brain stimulation.
• Evidence for treatment is limited; individualized, multidisciplinary approaches yield the best outcomes.

Myoclonus is best managed by a team familiar with its many faces—ensuring that patients receive accurate diagnosis, tailored therapy, and the best possible quality of life.