Epilepsy with myoclonic absences
Incidence
The syndrome is rare. Although figures of incidence or prevalence of epilepsy with myoclonic absences are unknown, this syndrome was found in 0.5% to 1% of a selected population of epileptics patients. A family history of seizure disorders can be found in about one fourth of cases reported.
Clinical Characteristics
Epilepsy with myoclonic absences is a rare form of epilepsy. It happens more in boys and approximately 25 per cent of patients will have another family member with a form of epilepsy. The underlying cause of this epilepsy syndrome is unknown. It is considered an epileptic syndrome. Myoclonic absences may be seen in children with brain abnormalities or with some genetic disorders. The average age of onset of epilepsy with myoclonic absences is 7 years (range: 2 to 12.5 years). Male preponderance has been described. About half of affected children are normal and half are mentally retarded prior to the onset of seizures. The manifestations are abrupt onset of absences accompanied by bilateral rhythmic myoclonic jerks of severe intensity. The loss of consciousness during the absence may be complete or partial. The seizure mainly involves muscles of the shoulders, arms, and legs; facial muscles are less involved. When facial myoclonias occur, they are more evident around the chin and mouth, whereas eyelid twitching is typically absent or rare. The movements may be sustained and progressive, being associated with tonic contraction, which is maximal in shoulder and deltoid muscles. The jerks and tonic contractions may be symmetrical or predominant on one side, causing turning of the head and body. Autonomic manifestations such as arrest of respiratory movement and urinary incontinence may also be present. Each episode of myoclonic absences may last from 10 to 60 seconds. The seizures may occur many times a day. Hyperventilation, awakening, and stimulation by intermittent light can precipitate the attack. During sleep, however, the myoclonic seizures decrease in frequency with the progression of sleep stages. Episodes of absence myoclonic status, though rare, have been described. Association with other types of seizures, such as generalized tonic-clonic, pure absence, and falling seizures, occurs in about two thirds of cases reported.
Precipitants
Hyperventilation, awakening, and stimulation by intermittent light can precipitate the attack.
Provocation Tests
Hyperventilation often trigger the episodes of absences associated with limb myoclonias.
Diagnostic Procedures
It is a clinical-EEG diagnosis. The description of the seizure given by the child and any eyewitnesses will help with identifying the particular seizure type in this epilepsy syndrome, together with the characteristic EEG. These children have brief episodes of loss of awareness with bilateral clonic jerking of the upper limbs, associated with rhythmic 3 cycles/second spike-wave discharges on the electroencephalogram.