Juvenile myoclonic epilepsy (JME). Janz syndrome
Incidence
Autosomal dominant. It has genetic heterogeneity. JME is said to account for between 5 and 10% of epilepsy. It is the most frequent form of hereditary grand mal epilepsy.
Clinical Characteristics
Juvenile myoclonic epilepsy is a subtype of idiopathic generalized epilepsy (IGE) affecting up to 25% of all individuals with IGE. This is a fairly common type of epilepsy which can develop between eight and 25 years of age, but usually starts between the ages of 12 and 16. It usually affects girls more commonly than boys. They have normal intelligence. It is considered an epileptic syndrome. The clinical features of JME differ significantly from those of generalized epilepsy with febrile seizures (GEFS), another IGE syndrome. Individuals with JME have afebrile seizures only, with onset in adolescence (rather than in childhood) and myoclonic jerks (usually absent in GEFS syndrome). Isolated myoclonic jerks are not necessarily a prelude to a major seizure and occur usually in the morning. There are three different types of seizure which can occur in this sort of epilepsy. Myoclonic seizures: These seizures usually happen soon after waking up and may happen when getting dressed or having breakfast. They may also happen in the evenings if the person is tired. Tonic clonic seizures: Two thirds of all people with juvenile myoclonic epilepsy will also have this type of seizure. These usually happen in the morning within one or two hours of waking up. This type of seizure is more likely to happen if the person has had sleep deprivation. Absence seizures: About one third to one half of children and teenagers will also have absence seizures. These episodes can happen at any time of the day, but they most frequently occur in the morning. The absences last from 10 – 40 seconds. A full and accurate history is very important in diagnosing this type of epilepsy. An EEG is very helpful in making a diagnosis, as this type of epilepsy is associated with some specific EEG patterns as well as photosensitivity.
Precipitants
Precipitated by fatigue or alcohol. Seizures are more likely to happen if a person does not get enough sleep or drinks too much alcohol.
Provocation Tests
Photosensitivity is common in people with JME. Photosensitivity can usually be seen in the EEG of people with JME.
Diagnostic Procedures
It is a combined clinical and EEG diagnosis. A full and accurate history is very important in diagnosing this type of epilepsy. An EEG is very helpful in making a diagnosis, as this type of epilepsy is associated with some specific EEG patterns as well as photosensitivity.