Atypical absence seizures

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By Olivier Dulac MD

Atypical absences are epileptic seizures that occur in children with severe learning and neurologic disabilities of epileptic encephalopathies, mainly, Lennox-Gastaut syndrome. They are distinct from typical absences in that onset and termination is slow, impairment of consciousness is mild, and they are often associated with significant tone disturbances. The ictal EEG shows diffuse spike waves that are slower than the typical absence, usually between 1.5 and 2.5 Hz. Patients with atypical absences also suffer from concurrent tonic, atonic, and other types of epileptic seizures according to the primary epileptic syndrome. Management is usually difficult, and prognosis is that of the underlying disorder. In this update, Dr. C P Panayiotopoulos, Consultant Emeritus in Clinical Neurophysiology and Epilepsy at St. Thomas’ Hospital in London, England, details the clinical manifestations, pathophysiology, EEG, neuroimaging, and optimal management of patients with atypical absence seizures and related epileptic syndromes.

Key points

  • Atypical absences are generalized epileptic seizures of mainly severe epilepsies in children with learning difficulties who also suffer from frequent seizures of another type.
  • Atypical absence seizures are characterized by a slow, insidious start and end with usually mild impairment of consciousness and significant atonic symptoms.
  • Ictal EEG shows diffuse spike and slow wave discharges with a varying range of frequencies at less than 2.5 Hz. Interictal EEG is often abnormal.
  • Atypical absences are common in Lennox-Gastaut syndrome and less prevalent in Dravet syndrome, epileptic encephalopathy with continuous spike-and-wave during sleep, and epilepsy with myoclonic-atonic seizures.
  • Prognosis and management is that of the underlying disease and syndrome.

In This Article

Historical note and nomenclature
Clinical manifestations
Clinical vignette
Differential diagnosis
Diagnostic workup
Syndromes and diseases in which the seizure type occurs
Prognosis and complications
References cited