Rational use of EEG in adults in clinical practice

The electroencephalogram (EEG) is still widely used for the diagnosis of several clinical conditions and symptoms. To assess the information provided by the EEG in relation to its duration, and to identify the shortest recording providing a conclusive report, the tracing was tested in 290 adult patients seen in a hospital neurophysiology unit for epilepsy (definite or uncertain), headache, head trauma, fainting, syncope, undefined loss of consciousness, vertigo, and cerebrovascular disease. Two neurophysiologists participating in the study read the same EEG independently. The record was based on a standardized timed sequence of montages. At each step any changes from the previous step were noted. Sixty-seven percent of the EEGs were coded as normal or aspecific, 24.1% were slow, and 8.6% were epileptiform. Normal tracings ranged from 38.8% (definite epilepsy) to 87.5% (vertigo), and epileptiform EEG from 0 (uncertain epilepsy) to 28.6% (definite epilepsy). The final report was clear in 80% of cases at the end of a 2-minute reading and almost 90% after 4 minutes. Hyperventilation and intermittent photic stimulation contributed little to the final report. Only for definite epilepsy were there changes along the whole sequence of montages. Thus, only for epilepsy need the EEG recordings last more than 20 minutes, whereas for the other clinical indications the total recording time could be limited to 4 minutes at most.