Absence seizure is a type of epilepsy characterized by sudden loss of consciousness for very short period followed by return of consciousness without any residual tiredness. This condition is also termed as petit mal seizure. Absence seizure is more common in children than to adults.
During an attack of absence seizure usually it looks like as if the affected person is staring into space for seconds. Children usually outgrow absence seizure by the time they attain puberty, however in some absence seizure with time may lead to other more serious varieties of seizures. The symptoms of absence seizure usually resolve with anti seizure medications.
Symptoms
Although the presenting symptoms of absence seizure vary from patient to patient, the most common presenting symptom of absence seizure is sudden loss of attention usually manifested as vacantly staring at the space usually not more than 15 seconds. The characteristic feature of absence seizure is that there is no recollection of the event along with no subsequent confusion, headache, tiredness or dizziness (postictal confusion). Sometimes during attack instead of vacant staring there could be a sudden interruption of current activities or only rolling of the eyeballs upwards. In some patients an attack can be aborted if he or she is addressed while most the affected patients remain unresponsive.
Other than the above mentioned characteristic feature absence seizure may present in different forms.
Absence seizure with mild clonic component which is characterized by accompanying abnormal movements, especially in the eyelid area or at the corners of the mouth
Absence seizure with atonic component which is characterized by accompanying loss of muscle power in some specific muscles manifested as loss of grip, relaxation of arms etc. Rarely the tone is significantly lost to cause complete loss of balance and fall.
Absence seizure with a tonic component which is characterized by accompanying tonic contraction of the muscles either symmetrically or asymmetrically, which results into arching of body forward with head drawn backward.
Absence seizure with automatism which is characterized by accompanying movements like lip licking to aimless walking without any awareness during an attack
Absence seizure with autonomic component in which, along with loss of consciousness, there is paleness or flushing of the face, profuse sweating leakage of urine and dilation of the pupils.
Often in children suffering from absence seizure the first symptom is a sudden unexplained decline in school performance and inability to pay attention.
The frequency of attacks varies from patient to patient, even in a single patient; sometimes about few hundred attacks can occur in a single day interrupting the daily routine to a severe degree.
In some cases absence seizure may lead to generalized tonic clonic seizure, severe degree of learning, behavioral problem and resulting social isolation.
Causes
The exact cause of absence seizure is yet to be identified, however genetic factors are known to play an important role. In about 90% of the cases it is found that hyperventilation plays an important role in absence seizure precipitation.
In all the type of seizure the normal electrical activity of nerve cells in the brain is disturbed because of repeated surges of electrical activities. In case of absence seizure the electrical surge typically repeats itself at an interval of three seconds.
Sometimes alteration in the level of signaling chemicals in the brain (neurotransmitters) may also play a role.
Risk factors
Common risk factors include
1. Age: return of consciousness of age are more susceptible to absence seizure.
2. Gender: usually seizure is more common in boys however in case of absence seizure girls are at increased risk.
3. Past history of febrile seizure during infancy or later increases the risk.
4. Family history: in about half of the patients suffering from absence seizure there is positive family history.
Treatment
Antiseizure drugs are the mainstay of treatment. Drugs are stopped if there is no attack of seizure for at least 2 years. Commonly prescribed drugs are ethosuximide, valproic acid and lamotrigine.