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Seizure Disorder, Absence

BASICS

  • Definition: Generalized nonmotor seizure characterized by brief lapses in awareness (blank staring, abrupt onset/offset, no aura/postictal phase).
  • Subtypes (ILAE):
  • Typical: Abrupt loss/return of awareness, 3 Hz, 5–30 sec, no postictal phase.
  • Atypical: Less abrupt, <2.5 Hz, 10–45 sec, may have mild postictal confusion.
  • Myoclonic: Abrupt loss of awareness + rhythmic jerks, 2.5–4.5 Hz, 10–60 sec.
  • Eyelid Myoclonia: Brief eyelid jerks, 4–6 Hz, <6 sec, usually retains awareness.

EPIDEMIOLOGY

  • Onset: 4–10 years (peak 5–7 years)
  • Gender: Female > male (2:1), except myoclonic (male > female)
  • Incidence: 6–8/100,000 children/year
  • Prevalence: 5–50/10,000

ETIOLOGY & PATHOPHYSIOLOGY

  • Genetic: Strong, multifactorial (75% monozygotic twin concordance)
  • Mutations: GABA receptors, T-type calcium channels, GLUT1 (worse prognosis)
  • Mechanism: Cortico-thalamocortical system, GABA hyperpolarization, T-type Ca²⁺ channels

RISK FACTORS

  • Poor medication adherence
  • Sleep deprivation
  • Alcohol
  • Medications lowering seizure threshold
  • Hyperventilation

COMMONLY ASSOCIATED CONDITIONS

  • Cognitive/learning impairment
  • Attention, visuospatial, verbal, memory, fine motor, executive, language difficulties
  • ADHD, anxiety, depression, low self-esteem

DIAGNOSIS

HISTORY

  • Sudden brief episodes of unresponsiveness/staring
  • Eyelid flutter, automatisms possible
  • No aura or postictal state (typical)
  • Teachers may report "daydreaming"
  • Forgetfulness in conversation, underperformance in school

PHYSICAL EXAM

  • Usually normal unless other neurologic abnormality present
  • Provocation: Hyperventilation for 3–5 min often triggers episodes
  • Note: Not photosensitive

DIFFERENTIAL DIAGNOSIS

  • Juvenile absence/myoclonic epilepsy
  • Focal seizures
  • ADHD
  • Confusional states
  • Psychogenic/nonepileptic spells
  • Migraine, panic attacks, breath-holding, febrile seizures

DIAGNOSTIC TESTS

  • Video-EEG: Diagnostic; spike-wave complexes (3 Hz typical, <2.5 Hz atypical)
  • Labs: Rule out metabolic, toxic, infectious (electrolytes, CBC, LFT, TSH)
  • Imaging: Not routinely indicated if exam/cognition normal; MRI if needed

TREATMENT

GENERAL MEASURES

  • Safety: Avoid unsupervised swimming, heights, driving, stoves, heavy machinery
  • State law: Know driving regulations for epilepsy

MEDICATION

First Line: - Ethosuximide (T-type calcium channel blocker): best for pure absence, fewer attentional effects - Valproic acid: Effective for absence & other generalized seizures; more adverse effects (attention, weight, teratogenicity) - Adverse effects: Hepatotoxicity, pancreatitis, teratogenicity, weight gain, tremor - Monitor: CBC, CMP, amylase, lipase - Lamotrigine: Alternative; less effective, but considered if other agents not tolerated

Second Line: - Lamotrigine, other agents

Avoid: Carbamazepine, oxcarbazepine, phenytoin, phenobarbital, tiagabine, vigabatrin, pregabalin, gabapentin (can worsen absence)

REFERRAL

  • Failure of seizure control after two AEDs or 1 year → refer to pediatric neurology/epileptologist

SPECIAL POPULATIONS

  • Children: Vitamin D supplement if on valproic acid (400–1,000 IU/day)
  • <2 years: Valproic acid risk for fatal hepatotoxicity is highest
  • Pregnancy: Avoid valproic acid; high risk of teratogenicity

SURGERY/OTHER

  • Medically refractory: Vagal nerve stimulator, epilepsy surgery
  • Ketogenic diet: Consider in drug-resistant epilepsy (can reduce seizure frequency by 50%)

ONGOING CARE

  • Monitor: Adverse effects, breakthrough seizures, labs per drug protocol
  • Patient/caregiver education: Risks, recognition/management of seizures, accident prevention
  • Resources: Seizure diary, action plan (Epilepsy Action Plan)
  • Support: “Sarah Jayne Has Staring Moments” book for children

PROGNOSIS

  • Childhood Absence Epilepsy (CAE): 56–84% remission
  • Worse prognosis: JAE, JME, those progressing to tonic-clonic or myoclonic
  • Typical absence: Usually remits by age 12

COMPLICATIONS

  • Absence status epilepticus: 5.8–9.4%
  • <10% progress to tonic-clonic seizures

ICD-10

  • G40.409: Other generalized epilepsy, not intractable, w/o status
  • G40.419: Other generalized epilepsy, intractable, w/o status
  • G40.401: Other generalized epilepsy, not intractable, w/ status

CLINICAL PEARLS

  • Ethosuximide and valproic acid are first-line
  • Absence seizures are not photosensitive
  • Daydreaming spells should be distinguished from absence seizures (test with unexpected stimuli)
  • Maintain seizure diary to identify triggers and efficacy
  • Seizure control failure after two AEDs → refer for further evaluation and alternative therapies