I recently had an eeg. today my nuero said he'd now like to order a full spectrum eeg. what's the difference?

Prolonged: it is more prolonged, ambulatory allowing for longer monitoring, making it more possible to catch occult seizures. about 15% of seizures are missed on regular EEG.

Full spectrum EEG: Expanded parameters of EEG analysis. Make sure the insurance will pay for this. Quantitative EEG analysis requires pre-certification. Use in clinical research may not be reimbursed by commercial carriers. Mapping for determination of seizure foci for the purpose of epilepsy surgery requires that you be a candidate for surgery, that the study be at least 20 minutes of recorded data

Simple explanation: A standard EEG might last 45 minutes, and thereby is going to often be falsely negative, missing events which are infrequent but real. The modern solution is a 72 hr ambulatory outpatient recording which provides far more complete information. Another far more expensive undertaking is an inpatient video recording within hospital.