eMedicine Specialties > Neurology > Seizures and Epilepsy

Absence Seizures: Differential Diagnoses & Workup

Author: Scott Segan, MD, Director of SBH Stroke Center and Attending Neurologist, St Barnabas Hospital
Contributor Information and Disclosures

Updated: Apr 7, 2009

Differential Diagnoses

Complex Partial Seizures
Psychogenic Nonepileptic Seizures
Confusional States and Acute Memory Disorders
Reflex Epilepsy
Febrile Seizures
Shuddering Attacks
First Seizure: Pediatric Perspective
Status Epilepticus
Migraine Variants

Other Problems to Be Considered

Breath-holding spells
Nonconvulsive generalized status epilepticus

Workup

Laboratory Studies

  • When evaluating a child for staring spells, laboratory tests for metabolic abnormalities or toxic or drug ingestion (especially in older children) may be indicated. If a clear history of the episodic nature of the attacks is obtained, then the EEG can be diagnostic and laboratory tests may not be necessary.
  • When evaluating a child with a developmental delay, or if the EEG reveals atypical absences, then a full work-up for the underlying cause of a symptomatic generalized epilepsy is indicated.

Imaging Studies

  • Neuroimaging findings are normal in idiopathic epilepsies by definition1,34 and therefore neuroimaging is not indicated if the typical clinical pattern is present.
  • Neuroimaging is often ordered by primary care providers and the emergency department, especially if a child presents with a generalized tonic-clonic seizure, to rule out significant structural causes of seizures. A normal result helps support the diagnosis of idiopathic epilepsy. For cryptogenic and symptomatic generalized epilepsies, neuroimaging can help in diagnosing of any underlying structural abnormality.
  • If imaging is performed, MRI is preferred to CT scanning. MRI is more sensitive for certain anatomic abnormalities. A review of 134 MRIs in patients with idiopathic generalized epilepsies found nonspecific abnormalities in 24%.35

Other Tests

The only diagnostic test for absence seizures is the EEG.

  • Findings in typical absence seizures include the following:
    • Background activity is normal.
      • In syndromes with frequent absence seizures, such as childhood absence epilepsy, a routine awake recording is often pathognomonic.
      • Bursts of frontally predominant, generalized 3-Hz spike-and-wave complexes are seen during the seizures.4
      • In syndromes with less frequent absence seizures (juvenile absence epilepsy or juvenile myoclonic epilepsy), an awake recording may be normal; a sleep or sleep-deprived recording may be needed.
    • Typical absence seizures have generalized 3-Hz spike-and-wave complexes (see Media file 2).

      EEG of a typical absence seizure with 3-Hz spike-...

      EEG of a typical absence seizure with 3-Hz spike-and-wave discharges.

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      EEG of a typical absence seizure with 3-Hz spike-...

      EEG of a typical absence seizure with 3-Hz spike-and-wave discharges.


      • The spike frequency is often faster at the onset, with a slight deceleration at the end.27 They can range from 2.5-6 Hz, with the faster frequencies seen in syndromes with older age of onset.
      • Bursts of generalized polyspikes and waves (multiple spike-and-slow-wave complexes) may also be seen31 , especially during sleep and in syndromes with older age of onset.
      • The onset and ending of these seizures are abrupt; no postictal EEG slowing is noted.
      • Hyperventilation often provokes these seizures and should be a routine part of all EEGs in children.
      • Photosensitivity may be present in idiopathic generalized epilepsies  and is more often seen in juvenile myoclonic epilepsy and childhood absence epilepsy than juvenile absence epilepsy.30
      • EEG video monitoring demonstrates that clinical seizure manifestations may lag behind the start of ictal EEG activity; bursts lasting less than 3 seconds are usually clinically silent. During the absence seizure, rhythmic eye blinks and mild clonic jerks may be present. As a seizure progresses, automatisms may be seen.33
      • Clinical and EEG features may vary considerably in different children.36
  • Findings in atypical absence seizures include the following:
    • Seizures are characterized by slow spike-and-wave paroxysms, classically 2.5 Hz (see Media file 3). The onset may be difficult to discern, and postictal EEG slowing may be noted.

      Slow spike-and-wave discharges (2.5 Hz). This is ...

      Slow spike-and-wave discharges (2.5 Hz). This is an interictal pattern in a child with seizures and developmental delay.

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      Slow spike-and-wave discharges (2.5 Hz). This is ...

      Slow spike-and-wave discharges (2.5 Hz). This is an interictal pattern in a child with seizures and developmental delay.

    • Background activity is often abnormal, reflecting the diffuse or multifocal underlying encephalopathy of symptomatic generalized epilepsy.
    • Generalized polyspike-and-wave complexes also may be present, and focal features may be observed.
    • The clinical correlation of generalized spike-and-wave complexes with clinical seizures is not as clear-cut as in typical absence seizures. Generalized slow spikes and waves may be present as an interictal pattern, as in Lennox-Gastaut syndrome.
    • EEG-video monitoring can show a more varied alteration of consciousness than in typical absence seizures. If the patient has underlying mental retardation, discerning changes in mental status also may be more difficult in atypical absence.
    • Changes in postural tone, most noticeably head nods, are common.

Ambulatory EEG monitoring over 24 hours may be useful to quantitate the number of seizures per day and their most likely times of occurrence.

More on Absence Seizures

Overview: Absence Seizures
Differential Diagnoses & Workup: Absence Seizures
Treatment & Medication: Absence Seizures
Follow-up: Absence Seizures
Multimedia: Absence Seizures
References
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Further Reading

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Keywords

absence seizure, petit mal seizures, generalized seizures, idiopathic generalized epilepsy, symptomatic generalized epilepsy, seizure treatment, epilepsy treatment, idiopathic generalized epilepsies, childhood absence epilepsy, pyknolepsy, juvenile absence epilepsy, juvenile myoclonic epilepsy, impulsive petit mal seizures, typical absence seizures, symptomatic generalized epilepsies, nonpyknoleptic seizures, spanioleptic absence seizures

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Contributor Information and Disclosures

Author

Scott Segan, MD, Director of SBH Stroke Center and Attending Neurologist, St Barnabas Hospital
Scott Segan, MD is a member of the following medical societies: American Academy of Neurology and American Epilepsy Society
Disclosure: UCB Pharma Honoraria Speaking and teaching

Medical Editor

Edward B Bromfield, MD, Associate Professor of Neurology, Faculty Member, Division of Sleep Medicine, Harvard Medical School; Chief, Division of EEG, Epilepsy and Sleep Neurology, Consulting Neurologist, Brigham and Women's Hospital
Edward B Bromfield, MD is a member of the following medical societies: American Academy of Neurology, American Clinical Neurophysiology Society, American Epilepsy Society, American Neurological Association, and Massachusetts Medical Society
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Jose E Cavazos, MD, PhD, FAAN, Associate Professor with Tenure, Departments of Neurology, Pharmacology, and Physiology, University of Texas Health Science Center at San Antonio; Co-Director, South Texas Comprehensive Epilepsy Center; Director of the Epilepsy Center, Audie L Murphy Veterans Affairs Medical Center
Jose E Cavazos, MD, PhD, FAAN is a member of the following medical societies: American Academy of Neurology, American Clinical Neurophysiology Society, American Epilepsy Society, and Society for Neuroscience
Disclosure: Nothing to disclose.

CME Editor

Selim R Benbadis, MD, Professor, Director of Comprehensive Epilepsy Program, Departments of Neurology and Neurosurgery, University of South Florida School of Medicine, Tampa General Hospital
Selim R Benbadis, MD is a member of the following medical societies: American Academy of Neurology, American Academy of Sleep Medicine, American Clinical Neurophysiology Society, American Epilepsy Society, and American Medical Association
Disclosure: Nothing to disclose.

Chief Editor

Selim R Benbadis, MD, Professor, Director of Comprehensive Epilepsy Program, Departments of Neurology and Neurosurgery, University of South Florida School of Medicine, Tampa General Hospital
Selim R Benbadis, MD is a member of the following medical societies: American Academy of Neurology, American Academy of Sleep Medicine, American Clinical Neurophysiology Society, American Epilepsy Society, and American Medical Association
Disclosure: Nothing to disclose.

 
 
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