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Historical note and nomenclature

Juvenile myoclonic epilepsy was first reported in France by Herpin (Herpin 1867). The terminology was variable until Janz and his colleagues in Germany reported 47 cases and proposed the name "impulsive petit mal" as a clinically definable epileptic syndrome (Janz and Matthes 1955; Janz and Christian 1957). The syndrome was later called juvenile myoclonic epilepsy (of Janz) in the English-speaking world (Asconape and Penry 1984; Delgado-Escueta and Enrile-Bacsal 1984). The International League Against Epilepsy suggested the equivalent terms "juvenile myoclonic epilepsy" and "impulsive petit mal" (Commission on Classification and Terminology of the International League Against Epilepsy 1989).

Clinical manifestations

Juvenile myoclonic epilepsy typically appears in the second decade. The age of onset ranges from 8 to 24 years, with peak onset between 12 and 18 years (Delgado-Escueta and Enrile-Bacsal 1984). It is characterized by myoclonic seizures, associated at times with generalized tonic-clonic seizures or absence seizures.

The cardinal seizure type is that of myoclonic jerks characterized by sudden, brief, bilaterally symmetrical and synchronous muscle contractions. The intermittent and involuntary shocklike contractions ("secousse") affect mainly the shoulder and upper extremities; much less commonly, the lower extremities or the entire body may also be involved. Myoclonic seizures may occur either singly or in clusters (Asconape and Penry 1984; Janz 1985). Objects may be thrown as a result of jerks, or, rarely, patients may fall. Consciousness remains unimpaired during myoclonic seizures, even if they occur in series or in myoclonic status epilepticus (Janz 1989).

Generalized tonic-clonic seizures appear after the onset of myoclonic seizures in the majority of cases (Asconape and Penry 1984). The average interval between the first myoclonic seizures and the beginning of tonic-clonic seizures is 3.3 years (Janz 1985). A convulsive seizure may begin with a series of myoclonic jerks of increasing intensity, followed by generalized myoclonus and then by generalized tonic-clonic seizures. This characteristic picture has been described as "myoclonic grand mal," "impulsive grand mal," and "clonic-tonic-clonic seizures" (Janz 1985).

Both the myoclonic seizures and generalized tonic-clonic seizures have a special circadian pattern, ie, they occur almost exclusively on or soon after awakening, either from all-night sleep or from a nap (Asconape and Penry 1984). The myoclonic and generalized tonic-clonic seizures are frequently precipitated by early awakening, sleep deprivation, emotional stress, alcohol consumption, recreational drug use, or photic provocation (Dreifuss 1989; Janz 1989). Occasionally, they may also occur sporadically during the daytime, or when the patients are tired and relaxed. Photosensitivity occurs in approximately one third of the patients (Asconape and Penry 1984; Dreifuss 1989). Seizure precipitation by complex neuropsychological tasks, especially when they require some kind of motor action ("praxis-induction"), has been shown to be associated with juvenile myoclonic epilepsy in up to half of the patients (Matsuoka et al 2000). As peri-oral reflex myoclonias elicited by talking and reading are also frequent in this syndrome (Mayer et al 2001), the presence of some reflex epileptic traits seems to be one of its characteristics.

Absence seizures, usually of typical variants, occur in 15% to 30% of afflicted patients and begin at a mean age of 11.5 years (Asconape and Penry 1984; Delgado-Escueta and Enrile-Bacsal 1984).

Intelligence usually remains normal in patients with juvenile myoclonic epilepsy (Janz 1985). However, associated immature personality, emotional instability, and inadequate social adjustment have been reported (Bech et al 1976).

Clinical vignette

No information was provided by the author.

Etiology

Juvenile myoclonic epilepsy is an idiopathic, hereditary form of epilepsy. Not a single case associated with organic brain pathology has been reported, although a history of febrile or isolated seizures in childhood can be obtained in a minority of cases (Janz 1985; 1989).

Fifty percent of patients have first- and second-degree relatives with epileptic seizures (Delgado-Escueta et al 1989); 80% of symptomatic and 6% of asymptomatic siblings have diffuse 4- to 6-Hz polyspike-and-wave complexes in their EEG. Twelve percent of asymptomatic siblings also have diffuse, nonspecific EEG abnormalities.

The concordance rate for monozygotic twins is 0.7 to 1.0, whereas that for dizygotic twins is the same as in siblings (Greenberg et al 1988). Despite long and intense genetic research, the genetics of the syndrome are not fully clarified. A polygenic mode of inheritance is the more likely cause as the different reflex epileptic traits that are frequent parts of the phenotype are also genetically determined. Evidence indicates that one gene involved in juvenile myoclonic epilepsy may be located on the short arm of chromosome 6 (Durner et al 1992), but it was not found in all investigated families (Elmslie et al 1996). Another candidate locus was found on chromosome 15q (Elmslie et al 1997) but, again, could not be found ubiquitously (Sander et al 1999). A relationship appears to exist between juvenile myoclonic epilepsy and other idiopathic age-related generalized epilepsies such as childhood absence epilepsy, epilepsy with grand mal seizures, and early childhood myoclonic epilepsy because more than one phenotype may exist in the same family.

Pathogenesis and pathophysiology

No specific pathophysiology has been identified for this idiopathic syndrome; however, there has been a recent increased interest in basic mechanisms of generalized epilepsies (Avoli et al 1990).

Epidemiology

The reported incidence of juvenile myoclonic epilepsy in epileptic populations has increased from 2.7% in 1957, to 5.4% in 1977, and to 11.9% in 1984 as awareness of this disease has increased (Janz 1985; Delgado-Escueta et al 1989). Diagnosis may still be commonly missed, largely because patients fail to report their myoclonic jerks, and physicians fail to specifically ask about them. In one study, definitive diagnosis of a series of patients referred to an epilepsy center was delayed by a mean of 14.5 years (Grunewald et al 1992).

Prevention

No information is available.

Differential diagnosis

The myoclonic seizures of juvenile myoclonic epilepsy are massive and bilaterally synchronous. They can be easily distinguished from other forms of nonepileptic myoclonus, which are characteristically focal and sporadic, as seen with the progressive myoclonus epilepsies (where there is coexistence of both nonepileptic myoclonus and epilepsy), certain lipid storage disorders, and postanoxic myoclonus. Myoclonic seizures occur in patients with other idiopathic generalized epilepsies such as the absence epilepsies, and epilepsy with grand mal seizures on awakening, but are not the most prominent features of these syndromes. The Lennox-Gastaut syndrome, epilepsy with myoclonic-astatic seizures, and epilepsy with myoclonic absences begin in childhood rather than adolescence and are associated with more frequent seizures and mental impairment. In the latter two, the myoclonic seizures usually involve the face and are associated with absences, whereas consciousness is not impaired during the myoclonic seizures of juvenile myoclonic epilepsy. Elicitation of the typical clinical features of juvenile myoclonic epilepsy (which requires the physician to ask specifically about jerks early in the morning) in association with the characteristic EEG pattern makes it difficult to miss this diagnosis.

Diagnostic workup

Because the jerks in juvenile myoclonic epilepsy are brief, without loss of consciousness, and take place in the morning soon after awakening, they are often interpreted as "nervousness" or "clumsiness" until generalized convulsions occur (Dreifuss 1989). Many patients ignore mild events and are unaware that they are abnormal.

Seventy-four percent of patients have epileptiform interictal EEG patterns (Obeid and Panayiotopoulos 1988). The typical interictal EEG displays paroxysmal, generalized, bilaterally symmetrical, 4- to 6-Hz polyspike-and-wave discharges (Asconape and Penry 1984). Classical 3-Hz spike-and-wave complexes or 3-Hz polyspike-and-wave complexes characteristic of typical absence seizures occur in approximately 17% of EEGs.

The ictal EEG is characterized by 10- to 16-Hz medium-high amplitude spikes followed by irregular slow waves. The number of spikes ranges from 5 to 20 per episode and correlates with the intensity rather than the duration of each seizure (Janz and Christian 1957).

Provocative measures, such as photic stimulation and sleep deprivation, can help elicit the characteristic EEG abnormalities. Recording during the process of awakening may be necessary for the diagnosis (Janz 1985). Sleep deprivation is very effective in precipitating seizures. Praxis-induction is found by neuropsychological testing during EEG (Matsuoka et al 2000), and perioral reflex myoclonias, unless observed during the interview with the patient, require a video-EEG investigation that includes reading aloud and free talking (Mayer et al 2001).

Polyspike-and-wave discharges are seen more frequently after nocturnal awakening than after morning awakening (Janz 1985). The incidence of photosensitivity has been reported to be as high as 30.5% (Janz 1985). Neurologic examination and neuroimaging studies are normal in this syndrome.

Prognosis

Juvenile myoclonic epilepsy does not often remit spontaneously. A relapse rate as high as 90% after discontinuation of antiepileptic drugs has been reported (Janz 1985), but the reflex epileptic phenomena may not have been considered (Schmidt 2000), and the evidence is not based on controlled investigations. However, lifelong therapy and lifestyle monitoring are today often considered necessary (Penry et al 1989).

The relapse rate during drug therapy, however, has been reported by others to be as high as 50% (Penry et al 1989). Those with predominantly myoclonic seizures during adolescence and a few isolated tonic-clonic seizures have the best chance of complete control.

Management

Both medical treatment and counseling are important in the management of juvenile myoclonic epilepsy. Monotherapy with valproate is the preferred treatment. It has been shown to be effective in controlling myoclonic, generalized tonic-clonic, and absence seizures (Penry et al 1989). The appropriateness of some of the newer antiepileptic drugs (lamotrigine, levetiracetam, and topiramate) in the treatment of this syndrome is still under investigation.

Clonazepam may be beneficial for controlling myoclonic seizures but not the generalized tonic-clonic seizures. Complete elimination of myoclonic seizures could cause additional disability by depriving patients of the warning jerks that herald the onset of generalized tonic-clonic seizures (Obeid and Panayiotopoulos 1989).

Seizures are usually precipitated by fatigue, noncompliance, stress, sleep deprivation, and alcohol consumption. Successful treatment is contingent on acceptance of appropriate limitations on lifestyle.

Pregnancy

Although no information is available that is specific to this syndrome and pregnancy, information is available on epilepsy and pregnancy.

Anesthesia

No information is available.

References

Asconape J, Penry JK. Some clinical and EEG aspects of benign juvenile myoclonic epilepsy. Epilepsia 1984;25:108-14.

Avoli M, Gloor P, Kostopoulos G, Naquet R, editors. Generalized epilepsy; neurobiological approaches. Boston: Birkhäuser, 1990:481.

Bech P, Kjaersgard Pedersen K, Simonsen N, Lund M. Personality in epilepsy. A multidimensional study of personality traits. Acta Neurol Scand 1976;54:348-58.

Commission on Classification and Terminology of the International League against Epilepsy. Proposal for revised classification of epilepsies and epileptic syndromes. Epilepsia 1989;30:389-99.

Delgado-Escueta AV, Enrile-Bacsal F. Juvenile myoclonic epilepsy of Janz. Neurology 1984;34:285-94.

Delgado-Escueta AV, Greenberg DA, et al. Mapping the gene for juvenile myoclonic epilepsy. Epilepsia 1989;30:S8-18.

Dreifuss FE. Juvenile myoclonic epilepsy: characteristics of a primary generalized epilepsy. Epilepsia 1989;30:S1-7.

Durner M, Janz D, Zingsem J, Greenberg DA. Possible association of juvenile myoclonic epilepsy with HLA-DRw6. Epilepsia 1992;33:814-6.

Elmslie FV, Rees M, Williamson MP, et al. Genetic mapping of a major susceptibility locus for juvenile myoclonic epilepsy on chromosome 15q. Hum Mol Genet 1997;6:1329-34.

Elmslie FV, Williamson MP, Rees M, et al. Linkage analysis of juvenile myoclonic epilepsy and microsatellite loci spanning 61 cM of huma chromosome 6p in 19 nuclear pedigrees provides no evidence for a susceptibility locus in this region. Am J Hum Genet 1996;59:653-63.

Greenberg DA, Delgado-Escueta AV, Maldonado HM, Widelitz H. Segregation analysis of juvenile myoclonic epilepsy. Genet Epidemiol 1988;5:81-94.

Grunewald RA, Chroni E, Panayiotopoulos CP. Delayed diagnosis of juvenile myoclonic epilepsy. J Neurol Neurosurg Psychiatry 1992;55:497-9.

Herpin TH. Des accès incomplets d’épilepsie. Paris: Baillière, 1867.

Janz D. Epilepsy with impulsive petit mal (juvenile myoclonic epilepsy). Acta Neurol Scand 1985;52:449-59.

Janz D. Juvenile myoclonic epilepsy. Cleve Clin J Med 1989;56:S23-33.

Janz D, Christian W. Impulsiv - petit mal. Deutsche Zeitschrift für Nervenheilkunde 1957;176:346-86.

Janz D, Matthes A. Die Propulsiv - petit mal - Epilepsie. New York: S Karger, 1955.

Matsuoka H, Takahashi T, Sasaki M, et al. Neuropsychological EEG activation in patients with epilepsy. Brain 2000;123:318-30.

Mayer T, Schroeder F, Wolf P. Reflex epileptic traits in juvenile myoclonic epilepsy. Epilepsia 2001;42(suppl 2):176-7.

Obeid T, Panayiotopoulos CP. Juvenile myoclonic epilepsy: a study in Saudi Arabia. Epilepsia 1988;29:280-2.

Obeid T, Panayiotopoulos CP. Clonazepam in juvenile myoclonic epilepsy. Epilepsia 1989;30:603-6.

Penry JK, Dean JC, Riela AR. Juvenile myoclonic epilepsy: long-term response to therapy. Epilepsia 1989;30:S19-23.

Sander T, Schulz H, Vieira-Saeker AM, et al. Evaluation of a putative major susceptibility locus for juvenile myoclonic epilepsy on chromosome 15q14. Am J Med Genet 1999;88:182-7.

Schmidt D. Response to antiepileptic drugs and the rate of relapse after discontinuation in juvenile myoclonic epilepsy. In: Schmitz D, Sander T, editors. Juvenile Myoclonic Epilepsy: The Janz Syndrome. Philadelphia: Wrightson, Petersfield, 2000:111-20.

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Abbreviations

EEG:electroencephalogram

ICD-9 code

345.1

Synonyms

Impulsive petit mal

Juvenile myoclonic epilepsy of janz

Benign juvenile myoclonic epilepsy

Herpin-Rabot-Janz syndrome

Jerk epilepsy

Myoclonic epilepsy of adolescence

Myoclonic petit mal

Associated disorders

Infantile spasms

West syndrome

Myoclonic absence

Lennox-Gastaut syndrome

Major keyword descriptors:

absence seizures

awakenings

chromosome 6

emotional instability

falls

febrile seizures

immaturity

myoclonic jerks

myoclonic seizures

myoclonus

naps

photosensitivity

polyspike-and-wave

seizures

sleep

sleep deprivation

tonic-clonic seizures

valproate

Minor keyword descriptors

epilepsy

petit-mal

Age of presentation

06-12 years

13-18 years

Age of typical presentation

06-12 years

13-18 years

Population groups preferentially affected

none selectively affected

Occupation groups preferentially affected

none selectively affected

Sex

male=female

Family history

family history may be obtained

Heredity

heredity may be a factor

heredity typical

Glossary

Juvenile myoclonic epilepsy

An epilepsy syndrome characterized by juvenile onset of myoclonic seizures that typically occur on awakening, with normal neurologic development.

Permuted topic, synonyms, subtopics

Juvenile myoclonic epilepsy

petit mal, Impulsive

epilepsy of Janz, Juvenile myoclonic

epilepsy, Benign juvenile myoclonic

epilepsy, Jerk

epilepsy of adolescence, Myoclonic

petit mal, Myoclonic

myoclonic epilepsy, Juvenile

Janz, Juvenile myoclonic epilepsy of

Rabot-Janz syndrome, Herpin-

Janz syndrome, Herpin-Rabot

adolescence, Myoclonic epilepsy of

Related summaries

Epilepsy

Juvenile absence epilepsy

Seizures induced by thinking

Sleep disorders

Differential diagnosis

progressive myoclonus epilepsies

lipid storage disorders

postanoxic myoclonus

absence epilepsies

epilepsy with grand mal seizures on awakening

Lennox-Gastaut syndrome

epilepsy with myoclonic-astatic seizures

epilepsy with myoclonic absences

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