Seizures and Epilepsy
The term seizure designates a clinical event that represents dysfunction of the central nervous system (CNS) and may signal a serious underlying abnormality.
In children the seizures usually result from a transient disturbance of brain function.
1. Classificationof seizure types
The ages of greatest risk for nonfebrile seizures are during infancy, childhood, and adolescence. The two primary forms of epilepsy are generalized seizures and partial seizures.
Partial seizures are the most common form of epilepsy in children.
Simple partial seizures (SPS)
During simple partial seizures the child remains conscious and is able to verbalize throughout the seizure. Most SPS are focal, asynchronous, clonic or tonic motor movements, such as forced deviation of the head and eyes to one side.
An SPS typically is short-lived, rarely persisting longer than 10 to 20 seconds.The EEG characteristicaly shows unilateral spikes or sharp waves in the anterior temporal region.
Complex partial seizures (CPS)
CPS initially may be similar in appearance to an SPS, but they are followed by impairment of consciousness. CPS may begin with a loss of consciousness. The average duration of a CPS is 1 to 2 minutes.
Automatisms are repetitive, stereotyped behaviors. These are the hallmark of CPS and occur in 50-75%. Automatisms follow the loss of consciousness, but unlike aura, the child is not aware of their presence.
Automatisms may include lip smacking, chewing, repetitive swallowing, excessive salivation, picking and pulling at clothing,constant rubbing of objects, and walking and running.
During the partial seizure,the epileptiform discharge may spread from the temporal lobe to throughout the cortex,causing a generalized tonic-clonic convulsion (termed secondary generalization).
During the complex partial seizures, the EEG is characterized by sharp waves or spike discharges in the anterior temporal or frontal lobe, or by multifocal spikes.
Simple absence seizures usually have their onset at 5 to 6 years of age and are characterized by brief (5-20 sec) lapses in consciousness, speech, or motor activity.
Absence seizures are not accompanied by an aura or a postictal drowsiness,but automatisms may occur(consisting of eye blinking or lip smacking). The EEG is characterized by 3 per second generalized spike and wave discharges.
A typical absence seizures are characterized by myoclonic movements of the face and body. The EEG shows 2-2.5 per second or 3.5-4.5 per second generalized spike and wave discharges.
Myoclonic seizures are characterized by brief,often repetitive,symmetric muscle contractions with loss of body tone.
Atonic seizures cause the child to fall because of a sudden loss of postural tone.
Tonic or clonic seizures are characterized by a sudden loss of consciousness and tonic-clonic, tonic, or clonic contractions. The child may develop perioral cyanosis and loss of bladder control. The seizure is followed by a 30-to 60-minute period of deep sleep and postictal headache.
A presumptive diagnosis of epilepsy generally is made from a history of spontaneous recurrent seizures and physical examination findings. The parent usually can give a good account ofthe seizure and whether it was generalized or focal in onset. The child may reveal the existence of aura, which signifies a focal onset.
Routine EEG may be useful in supporting a clinical diagnosis of epilepsy by showing epileptiform discharges (eg, spikes or sharp waves).
A definitive diagnosis of epilepsy can only be made using EEG-video monitoring. The correlation between clinical semiology and ictal EEG also allows epilepsy to be categorized as partial or generalized and for the zone of seizure onset to be located.
Ambulatory EEG allows the recording of electrographic seizures but does not permit correlation between EEG and seizure semiology. Ambulatory EEG can be a useful extension of routine EEG. It does not replace EEG-video monitoring.
Invasive EEG is necessary only when surgery is being considered and a regular EEG evaluation fails to identify the zone of seizure onset.
MRIis useful for excluding structural brain disorders.
Fasting blood glucose and serum calcium levels are indicated if the history suggests hypoglycemia or hypocalcemia as a cause of the seizure.
3. Management of nonfebrile seizures
Anticonvulsants are initiated following absence seizures, myoclonic seizures, and infantile spasms because the risk of recurrence is high.
A single afebrile tonic-clonic seizure has a 75% probability of not recurring if the neurologic examination and EEG are normal and there is no family history of epilepsy. Anticonvulsants are not advised following the initial tonic-clonic seizure in these children.
Felbamate (Felbatol) has a broad spectrum of activity in both partial and generalized seizures, but rare reports of fatal aplastic anemia and hepatic failure limit its use.
Gabapentin (Neurontin) has excellent tolerability. It is not protein bound, has no appreciable hepatic metabolism and is excreted by the kidneys.
Lamotrigine (Lamictal) has a broad spectrum of activity against multiple seizure types. Sedation is notably rare, and it has an alerting response in some patients. One side effect is a rash.
Topiramate (Topamax) has a broad spectrum of activity. Weight loss has been noted, which can be a desirable lateral side effect. Nephrolithiasis is rare; paresthesias are common.
Tiagabine (Gabitril) has no significant adverse side effects, but it has a relatively narrow spectrum of activity and must be titrated slowly.
Levetiracetam (Keppra) is unique among the new antiepileptic drugs because it is effective starting with the initial dose. It also has a mechanism of action that appears to be different from that of other antiepileptic drugs,and its tolerability and pharmacokinetics are very attractive. Drug interactions are minimal.
Fosphenytoin (Cerebyx) is a reformulated version of phenytoin for use in the treatment of status epilepticus.
Rectal diazepam (Diastat) can be self-administered by patients who have seizure clusters to abort impending status epilepticus.
Midazolam (Versed) and propofol (Diprivan) may soon become standard therapy for status epilepticus because of their very short half-life, which allows rapid titration based on the EEG.
Vagus nerve stimulation : The mechanism of action of vagus nerve stimulation (VNS) is likely mediated by the widespread afferent connections of the vagal nerve. Efficacy is comparable to adjunctive antiepileptic drugs. Efficacy may increase over time. VNS has no significant toxicity. Trials for its use in the treatment of depression are ongoing.
Epilepsy surgery : Seizures are intractable in approximately 20 percent of patients with epilepsy. Surgery is now a well-accepted modality for the treatment of medically intractable epilepsy.