What is the role of EEG in the diagnosis of first adult seizure?

Updated: Nov 30, 2017
  • Author: Eissa Ibrahim AlEissa, MD, MBBS; Chief Editor: Selim R Benbadis, MD  more...
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Answer

Electroencephalography (EEG) should be performed within 24 hours of the seizure, because this study is significantly more sensitive when obtained during that period (see the following images). [25] If the routine EEG findings are normal, a sleep-deprived EEG should be performed. Standard EEG detects epileptiform discharges in 29% of patients; however, standard EEG combined with sleep-deprived EEG shows epileptiform discharges in 48% of patients. [18]

An electroencephalogram (EEG) recording of a tempo An electroencephalogram (EEG) recording of a temporal lobe seizure. The ictal EEG pattern is shown in the rectangular areas.
An electroencephalogram (EEG) recording from a pat An electroencephalogram (EEG) recording from a patient with primary generalized epilepsy. A burst of bilateral spike and wave discharge is shown in the rectangular area.
An electroencephalogram (EEG) recording of a seizu An electroencephalogram (EEG) recording of a seizure from a subdural array in a patient evaluated for epilepsy surgery. The subdural electrodes record from the left anterior temporal (LAT), left middle temporal (LMT), and left posterior temporal (LPT) regions. The EEG seizure pattern is seen best in bipolar EEG channels LAT 3-4 and LMT 3-4 (rectangular areas).

EEG significantly improves diagnostic accuracy in patients with a first seizure. Using clinical data alone, King et al were able to determine that 8% of patients had primary generalized epilepsy, 39% had partial epilepsy, and 53% had unclassified seizures. [25] When using clinical and EEG data together, the investigators were able to determine that 23% of patients had primary generalized epilepsy, 53% had partial epilepsy, and 23% had unclassified seizures. [25]

Schreiner and Pohlman-Eden studied the value of an EEG taken within 48 hours of the first seizure in an adult. [38] They found that 38% of patients without seizure recurrence had normal EEGs, while only 10.2% of patients with seizure recurrence had normal EEGs. Focal epileptiform activities were found significantly more frequently (26.5% vs 13%) in patients with seizure recurrence than in patients without seizure recurrence.

Unfortunately, although EEG can be helpful, it is often harmful, because normal EEGs are frequently overread as epileptiform, leading to the misdiagnosis of seizures. [33, 39] The tendency to overread normal EEGs is common and has numerous causes. [40] The most common reason for misdiagnosis is that the history is not suggestive of seizures, but the entire diagnosis is essentially based on the EEG.


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