People with myoclonus often describe their signs and symptoms as jerks, shakes or spasms that are:

• Sudden
• Brief
• Involuntary
• Shock-like
• Variable in intensity and frequency
• Localized to one part of the body or all over the body
• Sometimes severe enough to interfere with eating, speaking or walking

Myoclonus may be caused by a variety of underlying problems. Doctors often separate the types of myoclonus based on their causes, which helps determine treatment. Types of myoclonus include the following categories.

Physiological myoclonus

This type of myoclonus occurs in normal, healthy people and rarely needs treatment. Examples include:

• Hiccups
• Sleep starts
• Shakes or spasms due to anxiety or exercise
• Infant muscle twitching during sleep or after a feeding

Essential myoclonus

Essential myoclonus occurs on its own, usually without other symptoms and without being related to any underlying illness. The cause of essential myoclonus is often unexplained (idiopathic) or, in some cases, hereditary.

Epileptic myoclonus

This type of myoclonus occurs as part of an epileptic disorder.

Symptomatic (secondary) myoclonus

Muscle jerks that occur as a result of an underlying medical condition, including:

• Head or spinal cord injury
• Infection
• Kidney or liver failure
• Lipid storage disease
• Chemical or drug poisoning
• Prolonged oxygen deprivation
• Medication reaction
• Autoimmune inflammatory conditions
• Metabolic disorders

Nervous system conditions that result in secondary myoclonus include:

• Stroke
• Brain tumor
• Huntington's disease
• Creutzfeldt-Jakob disease
• Alzheimer's disease
• Parkinson's disease and Lewy body dementia
• Corticobasal degeneration
• Frontotemporal dementia
• Multiple system atrophy