Long term or ambulatory EEG was developed to fill the gap between the regular, routine EEG and the intensive inpatient EEG monitoring for evaluation of difficult diagnostic cases of paroxysmal disorders (Seizures or seizure type activities).
A single 30 minutes EEG identifies about 50% of the abnormalities. Repeat EEGs and sleep deprived EEGs will identify another 25% of the abnormalities. The remaining patients with unexplained clinical events will not have abnormalities on the brief EEG to support the clinical diagnosis. The inpatient epilepsy monitoring unites have disadvantages of: hospitalization, restrict patients mobility, it is expensive and cumbersome. The mobile, outpatient long term recording devices are more convenient, readily available and less expensive. The recent electronic devices use computer chips and provide 24-96 hours of continuous 32 channel recording.
One of the advantages of ambulatory EEG is that long term recording can be obtained without the need for continuous monitoring and supervision by a technician. However this requires to properly applying the electrodes to the scalp. Secure the electrodes and the recording instrument so that it prevents mechanical and technical failures. Application of disc electrodes by collodion technique is currently the only method that will ensure stable long-term recording.
Analysis of the ambulatory EEG is made after the information from the recording device is down loaded to the computer. The reader will visually analyze the data at variable speeds and sensitivity for detecting ictal events or interictal spikes. Spike and seizure detection software is additionally employed to screen massive amount of accumulated EEG data for epileptiform abnormalities.