Myoclonus (Jerky Involuntary Movements)
Essential Facts for Patients

What is myoclonus?

Myoclonus refers to sudden, jerky involuntary movements. It can affect one or more muscles and can occur both when you are at rest and performing an action. These jerky movements commonly involve the upper limbs and face but may also occur in other body parts including the legs and trunk. Sometimes, sensory stimuli like light, touch, or sound can trigger myoclonus. These jerky movements can impact manual activities, balance, and walking, and may also cause anxiety or social embarrassment.

What are the causes of myoclonus?

Myoclonus can be a normal phenomenon, such as when sleep starts (hypnic jerks). Pathological myoclonus is caused by various neurological and non-neurological conditions or medications. 

These include:

• Epilepsy or seizure disorders
• Medical diseases such as renal failure, liver dysfunction, respiratory failure, thyroid disease or hypoxic brain injury. 
• Several medications used to treat epilepsy (phenytoin, carbamazepine), depression and other psychiatric diseases, Parkinson’s disease (amantadine)  
• Rare inherited diseases, such as myoclonus-dystonia and mitochondrial diseases
• Infection of the central nervous system (measles, prion diseases)
• Diseases outside the brain, involving the peripheral nerves (hemifacial spasm) or spinal cord may also result in myoclonus

Myoclonus may also be noted in people living with advanced dementia or parkinsonian syndromes. Sometimes, myoclonus may be a part of a functional neurological disorder. 

How Is It Diagnosed?

To diagnose myoclonus, doctors may use:

• Clinical evaluation: Assessing your symptoms and medical history. 
• Electrophysiological Tests: Including Electroencephalography (EEG) to check brain activity and Electromyography (EMG) to check muscle activity.
• Imaging: MRI or CT scans to look for brain abnormalities.
• Laboratory Tests: Blood tests to check for kidney or liver diseases and infections or inflammatory diseases. 
• Genetic Tests: DNA tests for inherited diseases, depending on the type of disease suspected one or more tests may be required.
• Lumbar puncture: Spinal fluid examination to look for infectious or inflammatory diseases.

Is there a treatment/ What are the treatments?

Addressing the cause of myoclonus is essential to plan the treatment. For myoclonus associated with medical diseases or medications, treatment of the underlying condition or changes in drugs often results in the resolution of myoclonus. For infectious diseases with specific treatment available, these are offered. In other situations, medications to control or mitigate the jerks maybe required. These include medications like benzodiazepines (clonazepam) and anti-seizure medications (valproic acid, levetiracetam, piracetam, zonisamide). The possible use, risks and benefits of these can be discussed with you by your treating teams. In certain situations, with myoclonus restricted to few body parts, botulinum toxin injections may be considered, such as in hemifacial spasm.

What can I expect as I live with a myoclonic disorder?

Depending on the underlying cause, myoclonus can be mild or severe. Myoclonus induced by medical disease and medications is generally reversible and the outcomes are tied to the prognosis of the underlying disease. Some of the inherited myoclonic disorders have a very slowly progressive course while others may result in significant difficulties in day-to-day activities, not only due to the myoclonus, but also contributed to by additional neurological problems. Identifying the cause of the disease through genetic or other tests, may help understand the future course or progression. Patient support and advocacy groups exist for specific myoclonic disorders, such as myoclonus-dystonia.