Petit is a French adjective meaning “small” or "little illness", a term dating from the late eighteenth century. Absence seizure also known petit mal seizure is named so because of its apparently less difficult to manage seizures in comparison to the grandmal (Generalised tonic clonic) seizures ( which may not be so actually if we see the nature of the underlying disease as a whole).
Absence seizure involves a brief (usually less than 20 seconds), sudden lapse of consciousness (generalised epileptic seizures). Absence seizures are more common in children than adults. Someone having an absence seizure may look like he or she is staring into space for a few seconds.
Compared with other types of epileptic seizures, absence seizures appear mild. But they can be dangerous. Children with a history of absence seizure must be supervised carefully while swimming or bathing because of the danger of drowning. Teens and adults may be restricted from driving and other potentially hazardous activities.
Some children who have absence seizures also have grand mal seizures. Many children outgrow absence seizures in their teen years.
Symptoms and Signs of absence seizures include:
Impairment of consciousness is the essential ictal element and may be the only clinical symptom, but this is often combined with other manifestations. The hallmark of the absence seizures is abrupt and sudden onset impairment of consciousness, interruption of ongoing activities, a blank stare, possibly a brief upward rotation of the eyes. If the patient is speaking, speech is slowed or interrupted, if walking, he or she stands transfixed; if eating, the food will stop on his way to the mouth. Usually the patient will be unresponsive when spoken to. In some, attacks are aborted when the patient is spoken to. The attack lasts from a few seconds to half a minute and evaporates as rapidly as it commenced.
1. Absence with impairment of consciousness only as per the above description
2. Absence with mild clonic components. Here the onset of the attack is indistinguishable from the above, but clonic components may occur in the eyelids, at the corner of the mouth, or in other muscle groups which may vary in severity from almost imperceptible movements to generalised myoclonic jerks. Objects held in the hand may be dropped.
3. Absence with atonic components. Here there may be a diminution in tone of muscles subserving posture as well as in the limbs leading to drooping of the head, occasionally slumping of the trunk, dropping of the arms, and relaxation of the grip. Rarely tone is sufficiently diminished to cause this person to fall.
4. Absence with tonic components. Here during the attack tonic muscular contraction may occur, leading to increase in muscle tone which may affect the extensor muscles or the flexor muscles symmetrically or asymmetrically. If the patient is standing the head may be drawn backward and the trunk may arch. This may lead to retropulsion. The head may tonically draw to one or another side.
5. Absence with automatisms. Purposeful or quasipurposeful movements occurring in the absence of awareness during an absence attack are frequent and may range from lip licking and swallowing to clothes fumbling or aimless walking. If spoken to the patient may grunt or to the spoken voice and when touched or tickled may rub the site. Automatisms are quite elaborate and may consist of combinations of the above described movements or may be so simple as to be missed by causal observation.
6. Absence with autonomic components. These may be pallor and less frequently flushing, sweating, dilatation of pupils and incontinence of urine.
Mixed forms of absence frequently occur. These seizures can happen a few times a day or in some cases hundreds of times a day, to the point that the person cannot concentrate in school or other situations requiring sustained, concentrated attention.
· Vacant stare
· Absence of motion without falling
· Lip smacking
· Eyelid flutters
· Chewing motions
· Hand movements
· Small movements of both arms
Absence seizures last only a few seconds. Full recovery is almost instantaneous. Afterward, there's no confusion, but also no memory of the incident. Some people experience dozens of these episodes each day, which interferes with their performance at school or work.
Children who are walking or doing other complex tasks during a seizure probably won't fall, though they'll be unaware.
Absence seizures in a child may occur for some time before an adult notices them, because they're so brief. A noticeable decline in a child's learning ability may be the first sign of this disorder. Teachers may comment about a child's inability to pay attention.
Absences seizures have two essential components:
· Clinically the impairment of consciousness (absence)
· EEG generalized spike-and-slow wave discharges.
Absence seizures are broadly divided in typical and atypical absence seizures. Typical absence seizures usually occur in the context of idiopathic generalised epilepsies and EEG shows fast >2.5 Hz generalised spike-wave discharges. The prefix “typical” is to differentiate them from atypical absences rather than to characterise them as "classical" or characteristic of any particular syndrome.
Atypical absence seizures:
· Occur only in the context of mainly severe symptomatic or cryptogenic epilepsies of children with learning difficulties who also suffer from frequent seizures of other types such as atonic, tonic and myoclonic.
· onset and termination is not so abrupt and changes in tone are more pronounced
· Ictal EEG is of slow less than 2.5 Hz spike and slow wave. The discharge is heterogeneous, often asymmetrical and may include irregular spike and slow wave complexes, fast and other paroxysmal activity. Background interictal EEG is usually abnormal.
When to see a doctor
· The first time you notice a seizure
· If you have a new type of seizure
Seek immediate medical attention:
· If you observe prolonged automatic behaviors — activities such as eating or moving without awareness — or prolonged confusion, possible symptoms of a condition called absence status epilepticus
· After any seizure lasting more than five minutes
Causes
Often, no underlying cause can be found for absence seizures. Many children appear to have a genetic predisposition to them. Sometimes hyperventilation can trigger an absence seizure.
Many children gradually outgrow absence seizures over months to years.
Complications
While most children outgrow absence seizures, some people may find that they are:
· Experiencing these types of seizures throughout life
· Eventually experiencing full convulsions (grand mal or generalized tonic-clonic seizures)
Other complications can include:
· Learning difficulties
· Absence status epilepticus, a condition in which seizure behavior lasts longer than a few minutes
Precipitating factors
Typical absences are easily induced by hyperventilation in more than 90% of the patients. This is a reliable test for the diagnosis of absence seizures: a patient suspected of typical absences should be asked to overbreathe for 3 min, counting his or her breaths. Intermittent photic stimulation may precipitate or facilitate absence seizures; eyelid myoclonia is a common clinical accompaniment.
These types of seizures are also known to occur to patients suffering with Porphyria, and can be triggered by stress or other Porphrin - inducing factors.
Syndromes of idiopathic generalised epilepsies with absence seizures
These are childhood absence epilepsy, juvenile absence epilepsy, epilepsy with myoclonic absences and juvenile myoclonic epilepsy. Other proposes syndromes are Jeavons syndrome (eyelid myoclonia with absences) and idiopathic generalised epilepsy with phantom absences
Tests and diagnosis
Some children experience episodes that resemble absence seizures, but aren't seizures. Such episodes usually can be interrupted by calling the child's name or by touching his or her shoulder. True absence seizures, on the other hand, can't be interrupted by voice or touch. Absence seizures may occur in the middle of a child's conversation or physical activity.
Absences seizures have two essential components:
· Clinically the impairment of consciousness (absence)
· EEG generalized spike-and-slow wave discharges.
A detailed description of the seizures and blood tests can help rule out other potential causes of seizures, such as a chemical imbalance or the presence of toxic substances. Other tests may include:
· Electroencephalography (EEG)
· Brain scans Tests such as magnetic resonance imaging (MRI) can produce detailed images of the brain, which can help rule out other types of problems, such as a stroke or a brain tumor.
Absence seizures are broadly divided in typical and atypical absence seizures. Typical absence seizures usually occur in the context of idiopathic generalised epilepsies and EEG shows fast >2.5 Hz generalised spike-wave discharges. The prefix “typical” is to differentiate them from atypical absences rather than to characterise them as "classical" or characteristic of any particular syndrome.
Atypical absence seizures:
· occur only in the context of mainly severe symptomatic or cryptogenic epilepsies of children with learning difficulties who also suffer from frequent seizures of other types such as atonic, tonic and myoclonic.
· onset and termination is not so abrupt and changes in tone are more pronounced
· ictal EEG is of slow less than 2.5 Hz spike and slow wave. The discharge is heterogeneous, often asymmetrical and may include irregular spike and slow wave complexes, fast and other paroxysmal activity. Background interictal EEG is usually abnormal.
Treatments and drugs
Finding the right medication and dosage can be challenging, requiring a period of trial and error.
Taking the medications on a regular schedule is crucial to maintaining proper drug levels in the blood.
Often, the first drug prescribed for absence seizures is ethosuximide.
However, other medications, such as valproic acid and lamotrigine, also are effective at controlling seizures. the lowest dose possible to start with and increase the dosage as needed to control the seizures is the norm. Most children can discontinue anti-seizure medications, under a doctor's supervision, after they've been seizure-free for two years.
The drug Lamictal has been linked to an increased risk of aseptic meningitis.
Women who need treatment for absence seizures are advised against using valproic acid while trying to conceive or during pregnancy. Women who can't achieve seizure control on any other medication need to discuss potential risks with their doctors.
Contraindicated drugs
The treatment of idiopathic generalized epilepsy is demanding because many antiepileptic drugs are either ineffective or exaggerate absences and myoclonic jerks. An antiepileptic drug is contraindicated not only when it exaggerates seizures but also when it is ineffective in controlling the seizures that it is supposed to treat. It may cause unnecessary adverse reactions and deprives the patient of the therapeutic effect that could be provided by another antiepileptic drug. Carbamazepine, vigabatrin, and tiagabine are contraindicated in the treatment of absence seizures, irrespective of cause and severity. GABA agonists vigabatrin and tiagabine are used to induce, not to treat, absence seizures and absence status epilepticus. Similarly, phenytoin, phenobarbital, gabapentin, and pregabalin should not be used in the treatment of absence seizures.
Limitations and research directions
In the treatment of absence seizures there is often insufficient evidence for which of the available medications has the best combination of safety and efficacy for a particular patient. Nor is it easily known how long a medication must be continued before an off-medication trial should be conducted to determine whether the individual has outgrown the absence seizures, as is often the case in children. To date there have been no published results of any large, double-blind, placebo-controlled studies comparing the efficacy and safety of these or any other medications for absence seizures. The studies that exist have been small and not produced clear conclusions.
Lifestyle and home remedies
A person with absence seizures may elect to wear a medical bracelet for identification for emergency medical reasons. The bracelet should state whom to contact in an emergency and what medications you use. It's also a good idea to let teachers, coaches and child care workers know about the seizures and tell them what to do in an emergency.
Even after they've been controlled with medication, seizures may affect areas of life, such as attention span and learning, will require close supervision for activities such as swimming. He or she will have to be seizure-free for reasonable lengths of time (intervals vary from state to state) before being able to drive.
Pathophysiology
The current understanding of the pathogenesis of absence seizures is based on animal models that generate generalised spike-and-wave discharges on EEG.
A reverberating circuit between the thalamus and cortex is the basis for this model, with the hypothesis being that
aberrant
rhythmic
oscillations
are generated in the circuit,
analogous to a mechanism that generates normal sleep spindles.
The reticulothalamic nucleus of the thalamus has been particularly implicated and contains a predominance of inhibitory GABA-containing interneurons.
In this case, GABA-mediated activity may trigger absence seizures by inducing prolonged hyperpolarisation and activating low-threshold Ca^2+ currents.
The concept of 't-type' or 'low-threshold' calcium channels playing a role in absence seizures is supported by the responsiveness of typical absence seizures to medicines such as ethosuximide, which is known to block these channels.
Multiple studies have been done in the attempt to identify a single gene locus for childhood absence epilepsy (CAE), juvenile myoclonic epilepsy (JME), or even the idiopathic generalised epilepsies (IGE) in general. Most identified genes associated with IGE involving absence seizures are for different types of ion channels (channelopathies). A gene for a component of GABA^A receptor has been implicated in a large family of JME with autosomal dominant inheritance. To date, CAE has been associated with defects in gamma-aminobutyric acid (GABA)^A receptor gamma2 subunit and voltage-gated Ca^2+ channel alpha-1A subunit (CACNA1A) among others.
Mutations in a gene that encodes voltage-gated chloride channel CLC-2 has been associated with CAE, juvenile absence epilepsy (JAE), and JME.
There have been multiple studies demonstrating a locus that may predispose to JME on chromosome 6p as well as 15q; the latter maps to the alpha-7 subunit of the neuronal nicotinic acetylcholine receptor (CHRNA7).
Recently, some cases of early-onset absence epilepsy have been attributed to mutations in the GLUT1 glucose transporter.
