Myoclonus

Myoclonus


Myoclonus or is a brief, involuntary twitching
of a muscle or a group of muscles. It describes a medical sign and, generally,
is not a diagnosis of a disease. These myoclonic twitches, jerks, or seizures
are usually caused by sudden muscle contractions or brief lapses of contraction. The most common circumstance under which they
occur is while falling asleep, but myoclonic jerks are also a sign of a number of neurological
disorders. Hiccups are also a kind of myoclonic jerk
specifically affecting the diaphragm. When a spasm is caused by another person it
is known as a “provoked spasm”. Shuddering attacks in babies also fall in
this category. Myoclonic jerks may occur alone or in sequence,
in a pattern or without pattern. They may occur infrequently or many times
each minute. Most often, myoclonus is one of several signs
in a wide variety of nervous system disorders such as multiple sclerosis, Parkinson’s disease,
Alzheimer’s disease, subacute sclerosing panencephalitis, Creutzfeldt-Jakob disease, serotonin toxicity,
some cases of Huntington’s disease, some forms of epilepsy, and occasionally in intracranial
hypotension. Some researchers indicate that jerks persistently
may even cause early tremors. In almost all instances in which myoclonus
is caused by central nervous system disease it is preceded by other symptoms; for instance,
in CJD it is generally a late-stage clinical feature that appears after the patient has
already started to exhibit gross neurological deficits. Anatomically, myoclonus may originate from
lesions of the cortex, subcortex or spinal cord. The presence of myoclonus above the foramen
magnum effectively excludes spinal myoclonus, but further localisation relies on further
investigation with electromyography and electroencephalography. Symptoms
Myoclonic seizure can be described as “jumps.” They are caused by rapid contraction and relaxation
of the muscles. People without epilepsy can suffer small but
similar jerks in the form of hiccups or brief twitches. These are perfectly normal. In someone with epilepsy, myoclonic seizures
can cause abnormal movements on both sides of the body at the same time. In reflex epilepsies, myoclonic seizures can
be brought on by flashing lights or other environmental triggers. 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 person’s ability to sleep, eat, talk, and walk. Myoclonic jerks commonly occur in individuals
with epilepsy. The most common types of myoclonus include
action, cortical reflex, essential, palatal, those seen in the progressive myoclonus epilepsies,
reticular reflex, sleep and stimulus-sensitive. Types
Epilepsy forms Cortical reflex myoclonus is thought to be
a type of epilepsy that originates in the cerebral cortex – the outer layer, or “gray
matter,” of the brain, responsible for much of the information processing that takes place
in the brain. In this type of myoclonus, jerks usually involve
only a few muscles in one part of the body, but jerks involving many muscles also may
occur. Cortical reflex myoclonus can be intensified
when patients attempt to move in a certain way or perceive a particular sensation. Essential myoclonus occurs in the absence
of epilepsy or other apparent abnormalities in the brain or nerves. It can occur randomly in people with no family
history, but it also can appear among members of the same family, indicating that it sometimes
may be an inherited disorder. Essential myoclonus tends to be stable without
increasing in severity over time. Some scientists speculate that some forms
of essential myoclonus may be a type of epilepsy with no known cause. Juvenile myoclonic epilepsy seizures usually
involve the neck, shoulders, and upper arms. These seizures typically occur shortly after
waking up. They normally begin between puberty and early
adulthood. They can usually be controlled with medication
but it must be taken for life. Lennox-Gastaut syndrome occurs in rare cases
beginning in early childhood and usually involving the face, neck, shoulders, and upper arms. In these cases, the seizures tend to be strong
and difficult to control. Progressive myoclonus epilepsy is a group
of diseases characterized by myoclonus, epileptic seizures, tonic-clonic seizures, and other
serious symptoms such as trouble walking or speaking. These rare disorders often get worse over
time and sometimes are fatal. Studies have identified at least three forms
of PME. Lafora disease is inherited as an autosomal
recessive disorder, meaning that the disease occurs only when a child inherits two copies
of a defective gene, one from each parent. Lafora disease is characterized by myoclonus,
epileptic seizures, and dementia. A second group of PME diseases belonging to
the class of cerebral storage diseases usually involves myoclonus, visual problems, dementia,
and dystonia. Another group of PME disorders in the class
of system degenerations often is accompanied by action myoclonus, seizures, and problems
with balance and walking. Many of these PME diseases begin in childhood
or adolescence. Treatment is not normally successful for any
extended period of time. Reticular reflex myoclonus is thought to be
a type of generalized epilepsy that originates in the brainstem, the part of the brain that
connects to the spinal cord and controls vital functions such as breathing and heartbeat. Myoclonic jerks usually affect the whole body,
with muscles on both sides of the body affected simultaneously. In some people, myoclonic jerks occur in only
a part of the body, such as the legs, with all the muscles in that part being involved
in each jerk. Reticular reflex myoclonus can be triggered
by either a voluntary movement or an external stimulus. Diaphragmatic Flutter
A very rare form includes the diaphragmatic flutter, or the Belly Dancer’s Syndrome. It was first discovered by Antony van Leeuwenhoek
in 1723. The condition characterizes spoken communication
that sounds like a short-breathed hiccup. These muscle spasms can recur dozens of times
per day. Rate of diaphragmatic contraction ranges between
35 and 480 contractions per minute, with the average rate found to be 150. Studies show that possible causes include
disruptions within the central or peripheral nervous systems, anxiety, nutritional disorder,
and certain pharmaceuticals. No single treatment has proven effective,
but most involve the blocking or crushing of the phrenic nerve. Only about 50 people in the world have been
diagnosed with it. One notable case is Chaz Moore of Colorado
Springs, Colorado, who was interviewed by CNN’s medical correspondent and respected
medical expert Dr. Sanjay Gupta. He tried several medications, but only one
worked: medical marijuana. Other forms
Action myoclonus is characterized by muscular jerking triggered or intensified by voluntary
movement or even the intention to move. It may be made worse by attempts at precise,
coordinated movements. Action myoclonus is the most disabling form
of myoclonus and can affect the arms, legs, face, and even the voice. This type of myoclonus often is caused by
brain damage that results from a lack of oxygen and blood flow to the brain when breathing
or heartbeat is temporarily stopped. Palatal myoclonus is a regular, rhythmic contraction
of one or both sides of the rear of the roof of the mouth, called the soft palate. These contractions may be accompanied by myoclonus
in other muscles, including those in the face, tongue, throat, and diaphragm. The contractions are very rapid, occurring
as often as 150 times a minute, and may persist during sleep. The condition usually appears in adults and
can last indefinitely. People with palatal myoclonus usually regard
it as a minor problem, although some occasionally complain of a “clicking” sound in the ear,
a noise made as the muscles in the soft palate contract. Middle Ear myoclonus occurs in the muscles
of the middle ear. These muscles may include the tensor tympani
and stapedius muscles. It can also involve the muscles surrounding
the Eustachian tube, which include the tensor veli palatini, levator veli palatini, and
salpingopharyngeus. Sufferers describe it as a thumping sound
or sensation in the ear. Spinal myoclonus is myoclonus originating
in the spinal cord, including segmental and propriospinal myoclonus. The latter is usually due to a thoracic generator
producing truncal flexion jerk. It is often stimulus-induced with a delay
due to the slow conducting propriospinal nerve fibers. Stimulus-sensitive myoclonus is triggered
by a variety of external events, including noise, movement, and light. Surprise may increase the sensitivity of the
patient. Sleep myoclonus occurs during the initial
phases of sleep, especially at the moment of dropping off to sleep. Some forms appear to be stimulus-sensitive. Some persons with sleep myoclonus are rarely
troubled by, or need treatment for, the condition. However, myoclonus may be a symptom in more
complex and disturbing sleep disorders, such as restless legs syndrome, and may require
treatment by a doctor. Myoclonus can also be associated with patients
suffering from Tourette syndrome. Cause
Rarely does myoclonus indicate anything other than arbitrary muscle contraction. Myoclonus may develop in response to infection,
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,, 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. Myoclonus can occur by itself, but most often
it is one of several symptoms associated with a wide variety of nervous system disorders. For example, myoclonic jerking may develop
in patients with multiple sclerosis, Parkinson’s disease, Alzheimer’s disease, Opsoclonus Myoclonus,
Creutzfeldt-Jakob disease, Lyme Disease, or lupus. Myoclonic jerks commonly occur in persons
with epilepsy, a disorder in which the electrical activity in the brain becomes disordered leading
to seizures. It is also found in MERRF, a rare mitochondrial
encephalomyopathy. Myoclonus can also be a coexisting condition
along with Tourette syndrome. 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 also can be caused by some
unrelated drugs such as anticholinergics. Opioids which have other neurotransmitter
impacts such as tramadol, pethidine, &c. can also cause jerks, but unlike the above are
not completely benign. Pathophysiology
Although some cases of myoclonus are caused by peripheral nervous system injury, most
myoclonus is caused by a disturbance of the central nervous system. Studies suggest that several locations in
the brain are involved in myoclonus. One such location, for example, 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. Some neurotransmitters may make the receiving
cell more sensitive, while others tend to make the receiving cell less sensitive. Laboratory studies suggest that an imbalance
between these chemicals may underlie myoclonus. Some researchers speculate that abnormalities
or deficiencies in the receptors for certain neurotransmitters may contribute to some forms
of myoclonus. Receptors that appear to be related to myoclonus
include those for two important inhibitory neurotransmitters: serotonin, which constricts
blood vessels and brings on sleep, and gamma-aminobutyric acid, which helps the brain maintain muscle
control. Other receptors with links to myoclonus include
those for benzodiazepines, drugs that induce sleep, and for glycine, an inhibitory neurotransmitter
that is important for the control of motor and sensory functions in the spinal cord. More research is needed to determine how these
receptor abnormalities cause or contribute to myoclonus. Treatment
In Asia, the mineral calcium, in the form of supplements or antacids, has been widely
known to dispel the commonly experienced sleep myoclonus, or hypnic jerk, and also restless
leg syndrome. Concerning more serious afflictions, the complex
origins of myoclonus may require the use of multiple drugs for effective treatment. Although some drugs have a limited effect
when used individually, they may have a greater effect when used with drugs that act on different
pathways or mechanisms in the brain. By combining several of these drugs, scientists
hope to achieve greater control of myoclonic symptoms. Some drugs currently being studied in different
combinations include clonazepam, sodium valproate, piracetam, and primidone. Hormonal therapy also may improve responses
to antimyoclonic drugs in some people. Some studies have shown that doses of 5-hydroxytryptophan
leads to improvement in patients with some types of action myoclonus and PME. These differences in the effect of 5-HTP on
patients with myoclonus have not yet been explained, but they may offer important clues
to underlying abnormalities in serotonin receptors. Many of the drugs used for myoclonus, such
as barbiturates, phenytoin and primidone, are also used to treat epilepsy. Barbiturates slow down the central nervous
system and cause tranquilizing or antiseizure effects. Phenytoin and primidone are effective antiepileptics
drugs, although phenytoin can cause liver failure or have other harmful long-term effects
in patients with PME. Sodium valproate is an alternative therapy
for myoclonus and can be used either alone or in combination with clonazepam. Although clonazepam and/or sodium valproate
are effective in the majority of patients with myoclonus, some people have adverse reactions
to these drugs. When patients are taking multiple medications,
the discontinuation of drugs suspected of causing myoclonus and treatment of metabolic
derangements may resolve some cases of myoclonus. When pharmacological treatment is indicated
anticonvulsants are the main line of treatment. Paradoxical reactions to treatment are notable. Drugs which most people respond to may in
other individuals worsen their symptoms. Sometimes this leads to the mistake of increasing
the dose, rather than decreasing or stopping the drug. Treatment of myoclonus focuses on medications
that may help reduce symptoms. Drugs used include sodium valproate, clonazepam,
the anticonvulsant levetiracetam, and piracetam. Dosages of clonazepam usually are increased
gradually until the patient improves or side effects become harmful. Drowsiness and loss of coordination are common
side effects. The beneficial effects of clonazepam may diminish
over time if the patient develops a tolerance to the drug. Prognosis
Although myoclonus is not a life-threatening condition, it may result in serious, debilitating
impairments. Action myoclonus, with its positive and negative
myoclonus components, is generally considered the most serious. It varies from person to person as to whether
it is lifelong. See also
Periodic limb movement disorder Benign fasciculation syndrome
Restless legs syndrome Fasciculation
Brain Zaps Clonus
References External links
The first version of this article was adapted from the public domain NINDS Myoclonus Information
Page. Please amend and adapt as needed. “Why do we twitch while falling asleep?” Myoclonus Fact Sheet, National Institute of
Neurological Disorders and Stroke

Be the first to comment

Leave a Reply

Your email address will not be published.


*