Closing the temporal blind spot: Six additional electrodes increase patient-level EEG abnormality detection by ~12

Area of Science:

• Neuroscience
• Clinical Neurophysiology
• Electroencephalography (EEG)

Background:

• The conventional 10-20 International System (IS) for EEG electrode placement has limitations in detecting certain abnormalities.
• The International Federation of Clinical Neurophysiology (IFCN) recommends a 25-channel array, incorporating additional inferior-temporal electrodes, to potentially improve diagnostic yield.

Purpose of the Study:

• To quantify the diagnostic yield increase of the IFCN 25-channel EEG array compared to the standard 10-20 system.
• To assess the impact of additional inferior-temporal electrodes on detecting interictal epileptiform discharges (IEDs) and focal slow activity (SA).

Main Methods:

• A comparative analysis of 258 adult EEGs using both the 10-20 system and the IFCN 25-channel array.
• Two blinded neurophysiologists reviewed EEGs twice after a washout period, with randomized reading lists to minimize bias.
• Abnormalities were classified by type and lobe, with agreement measured by Cohen's kappa and yield gain calculated as the detection-rate difference.

Main Results:

• The IFCN 25-channel array demonstrated an overall 11.5% increase in detecting EEG abnormalities compared to the 10-20 system.
• Significant gains were observed in detecting temporal interictal epileptiform discharges (IEDs) and temporal focal slow activity (SA).
• The addition of inferior-temporal electrodes yielded the most substantial improvements, particularly for temporal lobe abnormalities.

Conclusions:

• The IFCN 25-channel EEG array offers a significant improvement in detecting neurological abnormalities, especially in the temporal lobe.
• The enhanced electrode coverage addresses a known limitation of the 10-20 system.
• Routine adoption of the IFCN 25-channel array is supported for adult EEG practice to improve diagnostic yield with minimal additional setup time.