This condition is also often referred to as Janz syndrome. It is Janz and Christian in 1957 who gave the first detailed descritption of this condition. The entity was however known for more than 100 years ( Herpin 1867). Dr Janz suggested the term "impulsive petit mal" to the condition.
It is thought that about 2 to 5 % of all epileptic patients have Juvenile Myoclonic Epilepsy. Male to female ratio is about 50/50 ( some authors found a male preponderance while others found a female preponderance.)
The age of onset is usually in adolescence with 8 out of 10 cases beginning between the ages of 12 and 18. However any age can be seen (3 to 78...)
It is usually a single jerk of one limb or of the all body, that occur often in the morning when the child has been more tired than usual. The jerks are mostly bilateral, but may be minor enough for the child to include it in a movement. It often affects the extensors muscles and the classic story is the child who regular spills his morning chocolate or coffee because of a sudden jerk of his arm. some patients will actually fall. This a rare event and since the jerk is not associated with loss of consciousness, the child is able to remember the fall. The jerk is often brief enough for the child to be able to protect himself in case of a fall. It often when the first generalized tonic-clonic seizure occur that the child is brought to medical attention. Indeed, about 80 % of the patient with JME develop generalized seizures at some time during the evolution. The generalized seizures may occur before or after the onset of the myoclonic jerks. They are almost always in the morning on awakening. Up to one third of these children will also develop absences. All other types of seizures are rare in JME.
The EEG is very helpful in the diagnosis of this condition showing polyspikes and waves and photosensitivity.
This condition is genetic and runs in families.
The outcome for this condition is good as long as the patient remains on medications. Similar to juvenile absences, JME has a very high rate of relapse at discontinuation of treatment. The intellectual outcome is excellent.
The treatment uausally involves valproic acid that has been the drug of choice and is fairly ifficient at controlling the seizures. Clonazepam, phenytoin have also a role in the treatment of JME. New antiepileptic drugs such as Lamotrigene may well one day replace the older ones.