Chapter 12: Absence Seizures

Introduction

First described over 200 years ago by Tissot, childhood absence epilepsy (CAE) is a common pediatric epilepsy syndrome that affects otherwise normal children, with onset between ages 4 and 10 years and with a peak onset between 6 and 7 years.^1–5 Commonly misperceived as a “benign” epilepsy syndrome, patients with CAE demonstrate variable response to therapy, exhibit cognitive deficits, encounter elevated rates of accidental injury, demonstrate long-term psychosocial difficulties, and have variable remission rates. Similar to other epilepsies, the current therapeutic approach for children with CAE is empiric: an antiepileptic drug (AED) is selected based on available data and clinical experience, then titrated to an acceptable balance of seizure control and side effects.

Electroencephalography (EEG) is absolutely essential in the diagnosis and management of CAE, as well as other epilepsy types that include absence seizures. Video-electroencephalography monitoring (VEM) has several benefits over routine EEG in the diagnosis and management, including distinguishing absence seizures from nonepileptic events, identifying subtle clinical signs in seizures otherwise felt to be subclinical, and potentially identifying specific clinical signs during seizures that could affect outcome. This chapter will review CAE, with an emphasis on how EEG and VEM affect diagnosis, classification, study design, and treatment response.

Epidemiology

Approximately 10 to 15% of all children with epilepsy have CAE.^2,3 The annual incidence ranges from 6.3 to 8.0 per100,000 in children younger than 15 years.^4,5 CAE is often considered a “benign” epilepsy syndrome, likely to be outgrown, and with no risk of injury or other complications. However, accidental injury is common in CAE, with 20% of young adults with CAE reporting an injury during an absence seizure.⁶ The risk of accidental injury resulting from an absence seizure has been estimated to be 3% per person year.^7,8 Also, in contrast to the “benign” description, seizure remission is far from certain. The long-term remission rates for absence epilepsy range from 21 to 89%. This wide range likely results from inconsistent and variable study inclusion criteria, methods, follow-up length, and outcome definitions.^9,10 Furthermore, children with CAE have comorbid cognitive, behavioral, and/or psychosocial problems. Compared with matched controls, the mean percentiles in patients with absence epilepsy are lower for general cognitive functioning (25th vs 55th percentile), visuospatial skills (32nd vs 62nd percentile), nonverbal memory (50th vs 71st percentile), and delayed recall (24th vs 65th percentile).⁶ In a population-based study in Nova Scotia, psychosocial functioning, including social relationships, school function, and overall behavior, was found to be impaired in one third of children with CAE. Legal conviction rates and alcohol abuse were also elevated in young adults with a history of CAE, with 13% of CAE patients having a legal conviction excluding a traffic offense, compared with the province-wide conviction rate 5.4% of men and 1.2% of women in Nova Scotia. A history of alcohol abuse ...