It is also found in MERRF (Myoclonic Epilepsy with Ragged Red Fibers), a rare mitochondrial encephalomyopathy. Jerks of muscle groups, much of the body, or a series in rapid succession, which results in the person jerking bolt upright from a more relaxed sitting position is sometimes seen in ambulatory patients being treated with high doses of morphine, hydromorphone, and similar drugs, and is possibly a sign of high and/or rapidly increasing serum levels of these drugs. Myoclonic jerks caused by other opioids, such as tramadol and pethidine, may be less benign. Medications unrelated to opioids, such as anticholinergics, are known to cause myoclonic jerks. Pathophysiology
Most myoclonus is caused by a disturbance of the central nervous system. Some are from peripheral nervous system injury. Studies suggest several locations in the brain are involved in myoclonus. One is in the brainstem, close to structures that are responsible for the startle response, an automatic reaction to an unexpected stimulus involving rapid muscle contraction. The specific mechanisms underlying myoclonus are not yet fully understood. Scientists believe that some types of stimulus-sensitive myoclonus may involve overexcitability of the parts of the brain that control movement. These parts are interconnected in a series of feedback loops called motor pathways. These pathways facilitate and modulate communication between the brain and muscles. Key elements of this communication are chemicals known as neurotransmitters, which carry messages from one nerve cell, or neuron, to another. Neurotransmitters are released by neurons and attach themselves to receptors on parts of neighboring cells.
In reflex epilepsies, myoclonic seizures can be brought on by flashing lights or other environmental triggers (see photosensitive epilepsy). Familiar examples of normal myoclonus include hiccups and hypnic jerks that some people experience while drifting off to sleep. Severe cases of pathologic myoclonus can distort movement and severely limit a persons ability to sleep, eat, talk, and walk. Myoclonic jerks commonly occur in individuals with epilepsy. Cause
Myoclonus in healthy individuals may indicate nothing other than arbitrary muscle contraction. Myoclonus may also develop in response to infection, hyperosmolar hyperglycemic state, head or spinal cord injury, stroke, stress, brain tumors, kidney or liver failure, lipid storage disease, chemical or drug poisoning, as a side effect of certain drugs (such as tramadol, quinolones, benzodiazepine, gabapentin, sertraline, lamotrigine, opioids), or other disorders. Benign myoclonic movements are commonly seen during the induction of general anesthesia with intravenous medications such as etomidate and propofol. These are postulated to result from decreased inhibitory signaling from cranial neurons. Prolonged oxygen deprivation to the brain, hypoxia, may result in posthypoxic myoclonus. People with benign fasciculation syndrome can often experience myoclonic jerking of limbs, fingers and thumbs. Myoclonus can occur by itself, but most often as one of several symptoms associated with a variety of nervous system disorders, including multiple sclerosis, Parkinsons disease, Alzheimers disease, opsoclonus myoclonus, Creutzfeldt–Jakob disease, Lyme disease and lupus. Myoclonic jerks commonly occur in persons with epilepsy, a disorder in which the electrical activity in the brain becomes disordered leading to seizures.