Myoclonus is a medical term describing sudden, rapid, brief, involuntary jerking of a muscle or group of muscles. These shock-like movements can result from sudden muscle contractions, known as positive myoclonus, or abrupt losses of muscle tone, referred to as negative myoclonus. Since myoclonus can be caused by various neurological disorders, neurologists consider it a significant symptom to analyze.
Different forms of myoclonus may manifest, such as Parkinsonian Tremor, which is the most common cause of a resting tremor primarily affecting the distal muscles, like the pill-rolling tremor of the hand. It’s noted that cerebellar disease, unlike cerebrum issues, causes problems on the same side of the body as the cerebellar lesion. Titubation, for example, refers to the tremor of the head (and sometimes trunk) due to cerebellar disease.
In the case of psychogenic movements, these are often considered involuntary and performed without conscious awareness or effort. They can mimic organic movement disorders like tremor, dystonia, myoclonus, parkinsonism, tics, and paroxysmal dyskinesias. Even though a psychogenic movement disorder may resemble or accompany an organic disorder, it can be distinguished by a skilled professional.
Hypnic jerks, another form of myoclonus, are random and involuntary muscle spasms occurring as people fall asleep. Approximately 60 to 70 percent of the population has experienced these jerking movements at least once. These spasms are usually subtle, but some may be more pronounced, leading to sensations of falling or more significant spasms.
Action myoclonus–renal failure (AMRF) syndrome is a specific condition that causes episodes of involuntary muscle jerking or twitching and often kidney disease. Although its name refers to kidney problems, not everyone with the condition experiences kidney function issues. The movement problems associated with AMRF syndrome typically begin in adolescence or early adulthood.
Seizures, including those related to epilepsy in older adults, can also present as myoclonic jerks. They pose safety risks, such as falls or driving accidents, and are often associated with mood disorders like anxiety and depression. Recognizing the signs of seizures, like repetitive lip-smacking, hand movements, or jerking, is crucial for timely and effective treatment.
The term ‘myoclonus’ also encompasses various other involuntary movements. For instance, tics are sudden, rapid, repetitive movements or vocalizations. Simple motor tics include head shaking, eye blinking, sniffing, neck jerking, shoulder shrugging, and grimacing, while simple vocal tics can be coughs, throat clearing, or barking.
For more detailed information on myoclonus, visit Baylor Medicine, Stanford 25, Baylor Medicine – Psychogenic Movement Disorders, Hypnic Jerks Article, About AMRF Syndrome, 5 Signs of Epilepsy in Older Adults, Movement Disorders, and Harvard Health – Tics.
