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KembaraXtra-Medicine: Absence Seizures
Absence seizures are a form of generalized seizure characterized by brief episodes of impaired consciousness, typically presenting as sudden staring spells. These events usually last 20 to 30 seconds or less, begin and end abruptly, and are not followed by post-ictal confusion. Patients are usually unaware that a seizure has occurred and immediately resume their prior activity. The classic electroencephalographic (EEG) hallmark is a generalized 3-Hz spike-and-wave discharge, often provoked by hyperventilation.
Absence seizures are also referred to as childhood absence epilepsy or simply absence seizures and are classified under ICD-10-CM code G40.309 (generalized idiopathic epilepsy, not intractable, without status epilepticus). They represent up to 18% of pediatric epilepsy syndromes, with an incidence of approximately 1 to 10 cases per 100,000 population. The condition is more common in girls than boys. Onset typically occurs between 4 and 10 years of age, with a peak incidence around 6 to 7 years, and seizures often remit spontaneously by early adulthood.
On physical and neurologic examination, patients with absence seizures are usually entirely normal. During seizures, patients are briefly unresponsive and may exhibit subtle motor features such as eye blinking, lip smacking, or small hand movements (automatisms). Unlike focal seizures, absence seizures are not associated with an aura, post-ictal confusion, or prolonged recovery. They may occur many times per day and are commonly triggered by hyperventilation, such as during exercise or intentional over-breathing during EEG testing. Tonic-clonic seizures are not typical of classic childhood absence epilepsy; if present, alternative epilepsy syndromes should be considered.
The etiology of absence seizures is considered genetic, with dysfunction in thalamocortical circuits leading to abnormal synchronous neuronal firing. Because of this generalized mechanism, seizures involve both hemispheres simultaneously, which explains the abrupt onset, brief duration, and lack of post-ictal symptoms.
Diagnosis relies heavily on EEG, which is essential and often diagnostic. EEG performed with hyperventilation and photic stimulation typically provokes the characteristic generalized 3-Hz spike-and-wave pattern. Ambulatory EEG or video EEG monitoring may be used when diagnostic uncertainty exists, particularly to distinguish absence seizures from focal seizures with impaired awareness or nonepileptic staring spells. In patients with a classic clinical presentation and EEG findings, neuroimaging is often unnecessary; however, brain MRI should be performed if the EEG is atypical or if focal features are suspected. CT scans should generally be avoided in children due to radiation exposure and low diagnostic yield.
The differential diagnosis includes juvenile absence epilepsy, juvenile myoclonic epilepsy, focal seizures with impaired awareness (complex partial seizures), and nonepileptic staring episodes. Key distinguishing features include seizure duration (seconds in absence seizures vs minutes in focal seizures), lack of post-ictal confusion, frequent daily occurrence, and the characteristic EEG findings. Correct differentiation is critical, as some antiseizure medications used for focal epilepsy can worsen absence seizures.
Treatment outcomes are generally excellent. Ethosuximide is considered the first-line therapy based on the best available evidence, followed by valproic acid and lamotrigine as alternatives. Ethosuximide is particularly favored because of its effectiveness and relatively narrow side-effect profile for absence seizures. Valproic acid should be used cautiously, especially in girls and women of childbearing potential, due to teratogenic risks. Carbamazepine and phenytoin are contraindicated, as they may exacerbate absence seizures or provoke absence status epilepticus.
Children with recurrent absence seizures require chronic antiseizure therapy, but prognosis is favorable. Many children become seizure-free and can be considered for medication withdrawal after 1 to 2 years without seizures. Absence seizures commonly remit during adolescence, and epilepsy may be considered resolved after 10 years without seizures, including at least 5 years off medication.
Patients with absence seizures should be referred to a child neurologist, ideally one with expertise in epilepsy, for diagnosis confirmation and long-term management. Families should be educated about seizure recognition, medication adherence, and safety considerations. Driving restrictions apply to patients with ongoing seizures, and regulations vary by jurisdiction. Preventive strategies include avoiding sleep deprivation and alcohol, both of which may lower seizure threshold.
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