Myoclonic epilepsy

Myoclonic epilepsy
Specialty	Neurology

Myoclonic epilepsy refers to a family of epilepsies which present with myoclonus.

The Myoclonic Epilepsies

The Myoclonic Epilepsies

The term myoclonic had traditionally designated a large group of epilepsies characterized by repeated brief jerks, often responsible for multiple falls, severe seizures resistant to anti-epileptic drugs, and by an association with cognitive impairment . However, not all the ictal manifestations that cause falls are myoclonic, and not all myoclonic epilepsies predict poor outcome. myoclonic jerks are the only seizure type in but a minority of patients with myoclonic epilepsy which is commonly associated with generalized tonic-clonic seizures as well as generalized clonic, atypical absence, and atonic seizures . Tonic seizures are uncommon myoclonic epilepsies, but isolated tonic attacks during sleep are not rare in children with myoclonic-astatic epilepsy . As a result, confusion arouse in classifying myoclonic epilepsies, because they represent a broad group of diseases and epilepsy syndromes that differ in evolution and prognosis.

What is myoclonus?

Myoclonus, which is used to describe involuntary, jerky movements frequently involving antagonist muscles , can be classified physiologically as epileptic and nonepileptic. Epileptic myoclonus is an elementary electroclinical manifestation of epilepsy involving descending neurons, whose spatial (spread) or temporal (self-sustained repetition) amplification can trigger overt epileptic activity. Myoclonus can have focal, mutlifocal, or generalized distribution. Epileptic myoclonus is characterized neurophysiologically by myoclonic elecromyographic(EMG) burst ranging between 10 to 100 milliseconds, synchronous EMG bursts or silent periods on antagonist muscles, and an EEG correlate by scalp electrodes or burst-locked EEG averaging .

Etiology-

The vast majority of myoclonic epilepsies are idiopathic or cryptogenic, and genetic factors are important, as indicated by the frequency of epilepsy in family members. Mutations in the Beta1 and Alpha2 subunits of the sodium-channel receptor (SCN1B AND SCN2A) genes have been reported in a few patients with the MAE phenotype within generalized epilepsy with febrile seizures plus (GEFS+) families, as well as in patients with severe myoclonic epilepsy of infancy (Dravet syndrome) . A family with JME was found to harbor a mutations in the Alpha1 y-aminobutyric acid A GABA_a) receptor subunit (GABAA1) gene . These findings suggest that functional impairment of the ion channel may represent the pathophysiologic substrate for at least some of the nonprogressive myoclonic epilepsies. On the other hand, the progressive myoclonic epilepsies (PMEs) which are also genetically determined, follow an autosomal recessive inheritance and have been related to gene defects causing abnormal deposit material to accumulate in various organs including the brain.

Myoclonic Seizures

A sudden, brief, involuntary, shock-like muscular contraction that results in a body movement is referred to as myoclonus and my be epileptic or none epileptic. Myoclonic seizures are generalized seizures that occur either as part of an idiopathic epilepsy syndrome or in encephalopathic generalized epilepsy.Myoclonic seizures are characterized by sudden, involuntary brief, muscle contracts of the head, trunk, or limbs. They usually occur without detectable loss of consciousness and may be generalized, regional or focal. They may be irregular or erratic, symmetrical or asymmetrical, synchronous or asynchronous, and positive or negative (18). Myoclonic seizures are often bilateral jerks that vary from subtle restricted twitches of the periocular or facial muscles to massive movements, with generalized involvement of arms and legs accompanied by falling or retropulsion . They occur singly or in repeated clusters, with some cognitive impairment note during prolonged clusters of myoclonic status epilepticus . The associated features, rather than the semiology of the myoclonic seizures themselves, define the syndromes associated with myoclonic seizures.

Electrophysiology-The EEG

Myoclonic jerks associated with encephalopathic generalized epilepsy have high-amplitude, bisynchronous SSW or polyspike-and-wave discharge as the electrophysiologic correlate. A brief latency between shorts bursts and synchronized electromyographic potentials in agonist and antagonist muscles, and that of the corresponding spikes, occurs. The spike are time-locked events that are coupled with myoclonic jerks that follow. By using back-averaging techniques, latencies are found to occur between 21 and 80 milliseconds. When a myoclonic jerk is generated by subcortical structures, a generalized spike discharge follows the first electromyographic sign of myoclonus;however, in this case an epileptogenic phenomenon is disputed by some . Negative myoclonus caused by a lapse of tone, which can be seen only during antigravity posture, is coupled with either the slow wave or the second positive component of a polyspike-and-wave discharge . Myoclonic seizures have correlates with an electromyographic pattern, demonstrating a brief synchronous potential of less thn 50 milliseconds that is seen simultaneously in the invloved muscle groups. During the jerks, medium-to high-amplitude repetitive 16hz spikes are seen. The background activity of the interical EEG in patients with encephalopathic generalized epilepsy is characteristically diffusely slow. A unique EEG pattern is seen in early myoclonic encephalopathy and neonatal myoclonic seizures, with burst suppression or multiple paroxysmal abnormalities with random asynchronous attenuations

Clinical Correlation-

Most epilepsies with myoclonic seizures begin during the first 5 years of life. They are clinically and etiologically heterogeneous, and represent groups of disorders that may occur in many epilepsy types and syndromes from early infancy into adulthood. Myoclonic seizures must be differentiated from infantile spasms, partial seizures with tonic posturing and non-epileptic conditions, and difficulty may arrive in differentiating massive myoclonic seizures from tonic and atonic seizures. Causes of myoclonic seizures vary greatly from acquired causes of almost any etiology to familial epilepsies with varied inheritance patterns. The are subgroups of patients with idiopathic generalized epilepsy with refractory myoclonic seizures and developmental delay, yet with a genetic component. Myoclonic-astatic epilepsy and severe phenotypes of generalized epilepsy with febrile seizures plus (GEFS+) which mimic patients with encephalopathic generalized epilepsy, but with no discernible etiology and a genetic foundation for expression. Epilepsy with myoclonic astatic seizures is a syndrome intermediate between idiopathic and encephalopathic generalized epilepsy, with febrile seizures and subsequent myoclonic jerks during childhood that involve mainly the axial muscles, more than the face, upper trunk, and arms with jerks strong enough to cause patients to fall(astatic seizures). Similarly, epilepsy with myoclonic absences is characterized by prolonged absence seizures with prominent rhythmic generalized myoclonic jerks involving both shoulders, arms, and legs, which may repeat at 3Hz during activation techniques, distinguishing myoclonic absence from childhood absence epilepsy.

Pathophysiology-

It has been hypothesized that myoclonic seizures are produced by cortical and subcortical generator involving thalamocortical and reticular projections. Because of the wide variety of mechanisms associated with clinical expression of myoclonic seizures, no single pathology has been identified. In patients with encephalopathic generalized epilepsy, a wide range of pathologic substrates may exist, although frontal lobe abnormalities may preferentially occur . Genetic predisposition and/or the presence of a structural lesion underpin the best described pathphysiologic mechanism for myoclonic seizures, with various modes of inheritance and the progressive myoclonic epilepsy syndromes have isolated gene loci involved in the majority of the disorders . Myoclonic seizures assoicated with chromosomal abnormalities, mutant mitochondrial DNA, ion channelopathies, and defects of neurotransmitter systems form a wide variety of genetic influences that are reported.

Treatment-

Valproate has broad-spectrum efficacy, with patient with myoclonic seizures responding in the majority of cases. Benzodiazepines, valproate, topirmate, zonisamide, and levetiracetam may all be effective AEDs in paitent with myoclonic seizures. Lamotrigine may either be effective or aggravate myoclonic seizures. The ketogenic diet should be considered if AEDs are innfective for mycolonic seizures.

'Lennox-Gastaut Syndrome'

Lennox-Gastaut syndrome is one of the most unfavorable and severe form of epilepsey due to its lack of response to medication. #5 Defined by three characteristics: multiple seizure types, a distinctive brain-wave pattern and mental deficts(ranging from slight to profound) (Reference #13) Myolclonic seizures occur in 30% of patients with LGS, the term for those with such seizures is myoclonic variant of LGS #3

1.)Symptoms

• The usage of the Electroencephalography has been very important in understanding the brain activity of Lennox-Gastaut. (Niedermeyer article). EEGs show that it is characterized with slow spike-wave complexities(Niedermeyer). Meaning that, those with LGS show generally increased amount of slow activity brain waves (#3).

• Multiple forms of seziures are seen in those suffering from Lennox-Gastaut, making Lennox-Gastaunt such a severe syndrome. These include: tonic-clonic seizure, atonic seizure , myoclonic, absence seizure, chronic (rapidly repetice clonic movements), hemiclonic, atypical seizures (with slow spike-waves) (Niermeyer & #13)

• Along with the various seizures the disorder is assoicated with intellecual deficits are associated with it as well (except if the seizure onset is past age ten) (Niedermeyer). These deficits can range from slight to profound in impariment. (#13) This cognitive impairment often does not become apparemt itil later in the disorder (#3).

• Often times there are epileptic syndromes and diseases that mimic that of LGS including: myoclonic epilepsies of early childhood, atypical partial benign epilepsy of childhood, epilepsy with electrical status epilepticus during slow-wave sleep, neuronal ceroid lipofuscinosis, and Angelman syndrome (#3).

The most common include those with myoclonic symptoms:

a.) Myoclonic Astatic Epilepsy: A syndrome characterized by myoclonic, astatic, typical absence and tonic-clonic seizures that develops between one and five years of age. (#3) The distinction with LGS and this syndrome is not always clearm however thos with myoclonc-astatic have better seziure control and mental development than those with LGS (#3)

b.) Atypical Partial Benign Epilepsy: A syndrome characterized by myoclonic and atonic seizure clusters lasting between 2–4 weeks between the ages of two and six years of age (#3). Unlike LGS those with this syndrome usually have seizures that remit before the age of ten, and mental development regression is not signficant (#3).

c.) Angelman Syndrome: A syndrome characterized by microcephaly, flat occiput, severe metal retardation (like that of LGS), ataxia, jerky limb movements (myoclonus), and a cheerful dispostion (#3). This syndrome developes much earlier than LGS with first seizures occuring in infancy (#3).

2.) Causes

• There is no known direct primary cause for the syndrome, however there are many underlying casuse for sympotmatic Lennox:

Encephalitis and / or meningitis

Encephalopathy

Traumatic brain injury

Disease and / or developmental disorder

Malformation of the brain

Tuberous sclerosis

Trauma or injury at birth

Hypoxia ischemia injury

Lesions in the frontal lobe

Hereditary metabolic diseases (#14)

However, in many cases there is no know particular cause found for the development of the disease.

3.) Onset/Prevance/Prognosis

• Onset is in children, the first seizure happens between one and eight years of life(#3),most commonly developing at a peak between the ages of three and five, with a higher prevances amoung males than females (#3,#13). A rare disorder, Lennox-Gastaut occurs in 0.3 of 1,000 births. However, the symptoms may not always develop in childhood (#6).

• In about 25% of childhood cases of LGS there is normal neurologically prior to the oneset, whereas in 30-41% of cases LGS is preceded by West Syndrome (#3).

• Unlike other childhood epilpetic syndromes that tend to go into remission or stop all together by adolscence, Lennox-Gastaut are usually present in the rest of one's life once they occur (#6). Many with the disorder never are able to have independent adult lives with seizures that occur daily (#3). The prognosis of somone with normal mental health development is poor with LGS, however it should be noted, that the age of seizure onset is usally the best correlation to mental outcome, those with onset prior to age three show severe mental degression (#3). The type of seizures experienced also have an impact on prognosis with seizure types of myoclonic or atypical absence forms being more hopeful in prognosis (#3).

4.) Treatment

• Lennox-Gastuant is a particualar tricky syndrome to treat, usually multimodial forms are required. Even with multiple forms of treatment, total control of the seizures is a rarity (#13).

  a.) Medication

Generally, LGS has a bad reputation for having little to no response towards antiepileptic medications (Niedermeyer). However, usage of medications is usually administered, these medications include: Anticonvulsants, anesthetics, steroids such as prednosolone, valproates, benzodiazepines,and felbamate (#14). With regard to medications considerations must be made to treat the seizures best as possible while avioding negative side effects also it is important to note that treatment from a medical standpoint may be very difficult due to periods of active verus' inactive siezure periods(#13). Co-morbidity with intellecual deficts should also be respected.

  b.) Surgery

• The usage of corpus callosotomy may be used in severe cases of LGS (#13, #14) This surgery consists of severing the interconnecting network of nerves that allow the two hemispheres of the brain to be connected (#5).

• Those who have poor response to medication or are unlikey to receive psychosurgery can undergo vagus nerve stimulation (#5 and #6). This treatment involves inplanting a "battery", small device under the skin of the left side of the chest (#5). The battery when stimulated emits short repeated pulses of electrical stimulation thoughout the day (#5 and #6). The theory is that the pulse interfers with the abnormal elctrical pluses in the brain which result in the siezures in the first place, thus preventing the seizure before it can begin (#5 and #6). 15% of those with LGS use VNS (#5). Results of seizure control vary from patient to patient; 1/3 of VNS use experience massive improvement (more than 50%) , 1/3 report moderate control, and 1/3 report no change (#5).

  c.) Ketogenic Diet 

Known as the "long-chained triglyceride diet", the Ketogenic diet involves a strict regiment of high-fat, low-carbohydrate intake, this increases the amount of ketones in the body (#5 and #6). Ketones are formed with the body uses fat for energy instead of carbohydrates (#6). Doctors are unsure how this build up of ketones directly corresponds to reducing seizures, although some have theories (#5, #6, #14). Strict adherance to the diet is nesssary, sudden haults in the diet result in severe relapse of seizures, therefore patients who do well on the diet must be gradually taken off the diet over several months ( #5 and #6). Over half of children on the diet show a 50$ reduction in seizures and some chidren 10-15% become seizure-free ( #6). Side effects of long-term use of the diet include, high cholesterol, slowed growth, wieght gain, and more.

4.) Future research

A majority of research into LGS focuses on finding a primary cause for the disease as well as a productive treatment plan.

Progressive Myoclonic Epilepsy

Progressive myoclonic epilepsy (PME) is a group of myoclonic epilepsies with the subgroups being of several diseases sharing similar features. (webmd) These shared features include any of the following: worsening of symptoms as time progresses, Autosomal recessive inheritance, mutations of gene sequences leading to inhibitions of specific protein production, and reoccurring seizures (webmd). Progressive myoclonic epilepsy differs from myoclonic epilepsies by muscle contractions (myoclonus) being a separate entity from reoccurring seizures as well as the disease progressively getting worse over time and mostly ultimately leading to death (e.com)(webmd). There are four main sub-groups of PME being Lafora disease, Unverricht-Lundborg disease, myoclonic epilepsy with ragged-red fibers, and Batten disease (PME).

Lafora progressive myoclonus epilepsy

Lafora progressive myoclonus epilepsy (Lafora Disease, Lafora Body Disease) is a genetic disorder of the brain that causes reoccurring seizures and slow declination of intellectual ability (GHR). The common seizures that occur in individuals with Lafora disease include occipital seizures as well as grand mal seizures. Occipital seizures can cause hallucinations and even temporary blindness (GHR, PME). Grand mal seizures (tonic-clonic seizures) are myoclonic seizures that affect a large portion or even entirely of the individual's body, causing rigidness in the muscles, uncontrollable convulsions, and can cause the individual to fall into a state of unconsciousness (GHR). These seizures usually begin in late childhood or early adolescence, with noticeable symptoms being depression, periods of confusion, and speech difficulties (GHR). As time progresses, symptoms of some loss of intellectual ability occurs such as memory loss, slowed thought processes, and impaired judgment that make the ability to perform tasks normal for daily life very difficult (GHR). The loss of this ability takes only around one decade after the first appearance of symptoms, and the end result is death (GHR). This disease is an autosomal recessive trait, so both recessive genes from parents must be passed on and also must contain the gene mutations (GHR, PME). The specific genes that lead to Lafora disease are mutations in either the EPM2A gene or the NHLRC1 gene (GHR). The EPM2A gene is responsible for making the protein Laforin, and the mutation denies the cell ability to produce this protein (GHR). The NHLRC1 gene likewise, is responsible for making the protein malin, and the mutation in the gene makes the sequence no longer code for the protein production (GHR). Laforin and malin together help regulate glycogen production, preventing a dangerous buildup of glycogen in cells (GHR). Abnormal formations of these glycogen deposits (Lafora bodies) cannot be broken down for fuel supply in the cell, and this buildup kills nerve cells, which leads to brain dysfunction (GHR). Lafora disease generally progresses slower in individuals with NHLRC1 gene mutation as opposed to the EPM2A gene, which is a phenomenon that is not yet clearly distinguished (GHR).

Unverricht-Lundborg Disease

Unverricht-Lundborg Disease (Baltic myoclonus, Mediterranean myoclonus) is a form of myoclonus epilepsy that is first seen in children as young as six, and occurs after stimuli to light, excessive exercise, stress, and other stimuli (GHR). The seizures experienced are grand mal seizures which involve the entire body in muscle contractions, and can lead to unconsciousness in some cases (GHR). Without medication, these seizures will advance over the span of several years to become severe enough to interfere with normal daily activities such as driving and walking (GHR). In addition to this, progression of this disease may lead to slight declines of intellectual ability, involuntary rhythmic shaking, depression, difficulties with speech, and declines in coordination (e.com). This is the most common of the progressive myoclonic epilepsies, and although worldwide statistics are unknown, the disease has a prevalence in 1 in 25000 in Finland, which is where the disease is most common (GHR). Unverricht-Lundborg disease is an autosomal recessive disease, and thus is inherited (GHR). The mutated gene that causes the disease is the CSTB gene, which is responsible for coding for the cyctatin B protein. This protein is involved with decreasing the activity of the enzyme cathepsins. Cathepsins help break down certain proteins in lysosomes, and with less cyctatin B proteins, the cathepsins are thought to be able to break down important proteins in the cytoplasm (GHR). The CSTB gene is a 12 base pair sequence 5'CCC-CGC-CCC-CGC3', and this repeats only a couple of times in healthy individuals (e.com). The mutation is an extended repeat of this 12 base pair sequence, containing 30 to 100 repeats (e.com). This repeat sequence is located in the promoter region 175 base pairs upstream from the AUG initiation sequence (e.com). Treatment of this disease is shown to lighten symptoms and slow progression (e.com). The standard treatment currently available is valproic acid complimentary with clonazepam or piracetam (e.com).

Myoclonic Epilepsy with Ragged-Red Fibers

Myoclonic epilepsy with ragged-red fibers (MERRF) is a myoclonic epilepsy that affects muscle and nerve cells, and it first appears in late childhood or adolescence (GHR). The typical signs of MERRF are twitching in the muscles, progressive stiffness, and general weakness (GHR). The term 'ragged-red fibers' stems from the fact that individuals with the disease have abnormal muscle cells in design. The symptoms of MERRF include ataxia, peripheral neuropathy, recurrent seizures, loss of intellectual function, and also may develop optic atrophy and loss of hearing (GHR). Less commonly individuals develop cardiomyopathy, or short stature and abnormalities in the heart (PME). This disease is inherited by maternal inheritance because the disease is found in mitochondrial DNA (mtDNA), which is found in egg cells and not sperm cells (GHR)(PME). The specific genes that form mutations are the MT-TK, MT-TL1, MT-TH, and MT-TS1 genes, with four fifths of the mutations occurring in the MT-TK gene (PME). The mutations of the genes affect the functioning of the mitochondria to use oxygen to produce energy, and also impair the ability of producing certain proteins in the mitochondria (PME). This mostly affects the cells in the body that are high energy, which include brain and muscle cells (PME)(GHR). This is still a disease that needs further research to determine more specifically what occurs in the mitochondria of the cells (PME).

Batten Disease

Batten Disease is a form of neuronal ceroid lipofuscinoses (NCL) that is prevalent in children that first appears between the ages of 4 and 18 (GHR). The first sign of Batten disease is declination of vision which occurs normally before the age of ten, which leads to total blindness after rapid vision loss (GHR). The seizures in individuals usually begin after the beginning of vision impairments, anywhere from the ages of 5 to 18 (GHR). Individuals will also experience the declination of cognitive ability, along with behavioral and attention problems, troubles with speech, and difficulty sleeping (GHR). Another difficulty developed by affected individuals is typical issue that is shared with NCL diseases, which is the development of rigid, slow, and clumsy movement, that progresses into the inability to perform everyday tasks that is even extended to the ability to walk (GHR). In the United States, the prevalence of this disease is 1:50000 to 1:25000 individuals (GHR). This disease is an autosomal recessive disease, meaning it is passed on by the parents who both contain the mutated recessive gene (GHR). The affected gene is the CLN3 gene which codes for a protein that plays an important role in the survival of nerve cells, although the specific protein is still not known (GHR). While the role of the gene is unknown, it is expected that the mutation disrupt the functioning of lysosomes in nerve cells, making the buildup of lipopigment possible, which is a lipid that builds up abnormally in lysosomes, ultimately causing cellular death (GHR). Affected individuals usually live into their twenties, with a handful living into their thirties (GHR).

Refererences

Wyllie, Elaine (2006). The Treatment of Epilepsy. Lippincott, Williams and Wilkins. ISBN 0-7817-4995-6.