Myoclonus is characterized by the occurrence of brief muscle twitches. These are manifested by involuntary and sudden movements. There are different forms including sleep myoclonus, or secondary myoclonus which occurs in particular in epilepsy.

Myoclonus is a brief twitch of the muscle that causes involuntary, sudden and sudden movements. They can occur spontaneously or occur as a reaction to a stimulus such as noise or a flash of light. The twitching can occur in a single muscle or affect a group of muscles.

The usual example of myoclonus is hiccups, or phrenoglottic myoclonus. It is the result of a succession of involuntary muscle contractions.

Myoclonus can be caused by a sudden muscle contraction or by a sudden stop in muscle activity. These phenomena can have several explanations. Depending on the case, there are three types of myoclonus:

• physiological myoclonus, which are related to the functioning of the body;
• secondary myoclonus, which are caused by the occurrence of a disorder in the body;
• les myoclonies iatrogènes, which are the consequence of medical treatment.

The causes of physiological myoclonus

Myoclonus can be linked to the functioning of the body. We can for example quote:

• phrenoglottic myoclonus, better known as hiccups;
• sleep onset myoclonus, or sleep myoclonus, which manifests as a startle in sleep and which usually occurs during the first few minutes of falling asleep.

Other physiological causes have also been identified. These include anxiety, physical exercise and diet.

Causes of secondary myoclonus

Secondary myoclonus can be due to various disorders such as:

• epilepsy, a neurological condition in which myoclonus is one of the main signs;
• dementia, in particular during Creutzfeldt-Jakob disease, Alzheimer’s disease, diffuse Lewy body disease, frontotemporal dementia or Rett syndrome;
• spinocerebellar degeneration, which occurs in the context of several neurodegenerative diseases such as Parkinson’s disease, Huntington’s disease, Ramsay-Hunt syndrome or even Wilson’s disease;
• physical and hypoxic encephalopathies, cerebral dysfunctions which occur in particular during electric shock, heat stroke, hypoxia, traumatic brain injury and decompression sickness;
• toxic encephalopathies, cerebral damage which is notably the consequence of heavy metal poisoning;
• infections, especially in lethargic encephalitis, herpes simplex virus encephalitis, post-infectious encephalitis, malaria, syphilis and Lyme disease;
• certain metabolic disorders, such as hyperthyroidism, hepatic failure, renal failure, hypoglycemia, non-ketotic hyperglycemia and hyponatremia.

The causes of iatrogenic myoclonus

Myoclonus can sometimes be the result of medical treatment. It can, for example, follow on from:

• psychiatric treatment, especially when using lithium, antidepressants or neuroleptics;
• certain anti-infective treatments, in particular when using quinolones;
• certain cardiology treatments;
• the use of sleeping pills;
• the use of anticonvulsants;
• taking anesthetics.

The clinical manifestations of myoclonus vary from case to case. They can in particular vary in amplitude and frequency. In more severe cases, muscle twitching can be generalized with the onset of seizures.

When the myoclonus is generalized, persists or recurs, urgent medical consultation is recommended. The medical management makes it possible to identify and treat the cause of the myoclonus.

To define the origin of myoclonus, it is generally necessary to perform the electrophysiological recording of abnormal movements.

To relieve muscle twitching, symptomatic treatment can sometimes be implemented. This can be based on the use of different drugs:

• benzodiazepines, such as clonazepam, which are a class of psychotropic drugs;
• anti-epileptics such as valproate;
• nootropics such as piracetam;
• anticonvulsants such as leviracetam.