Electroencephalography (EEG) is the standard test used to aid a diagnosis of epilepsy. In this test, electrodes are fixed to a person's scalp and the spontaneous electrical activity going on in their brain is recorded. If a person has a seizure while they're wearing the electrodes, this will show on the scan. However, an EEG test on its own cannot be used to confirm or exclude epilepsy: it is possible for people with epilepsy to have perfectly "normal" EEGs, and also for people who do not have epilepsy to have "epileptic" patterns on their EEGs.

Because for many people not getting enough sleep increases their likelihood of having a seizure, doing an EEG while they are sleep-deprived can increase the likelihood of seeing epileptic activity. This won't necessarily be a seizure; it could be specific electrical activity patterns in the brain which do not cause physical symptoms. These include "focal discharges" and "spike-and-wave discharges".

A team of doctors in Glasgow have compared different ways of recording EEGs, to find out which is most useful for diagnosing epilepsy. They carried out EEGs in three different ways on 85 young adults who were being tested for possible epilepsy: routine EEG, sleep-deprived EEG, and EEG carried out during drug-induced sleep.

Thirty-nine percent of the patients had completely normal EEGs of all three types: no patterns typical of epilepsy were seen. Generalised spike-and-wave discharges were seen in 43% of patients in at least one EEG type, and focal discharges in 18% of patients.

Sleep-deprived EEG picked up the spike-and-wave patterns in 92% of the patients it was seen in, whereas routine EEG picked it up in only 58% of patients, and EEG during drug-induced sleep in 44%. This is a significant difference.

In nearly half the patients with focal discharges, the abnormalities were only visible on sleep-deprived EEG, not on the other two EEG types. Two patients showed focal activity in routine EEG only, and one in EEG during drug-induced sleep only.

Dr John-Paul Leach and his colleagues, writing in the September issue of the Journal of Neuroscience, Neurosurgery and Psychiatry, reminded doctors that sleep-deprived EEG is more likely than the other two types of EEG to pick up epileptic-type electrical brain activity. Using sleep-deprived EEG will reduce the likelihood of having to run the test again if it was inconclusive the first time. They said that sleep-deprivation was an easy and inexpensive way of increasing the likelihood of getting a useful, meaningful EEG, and recommended that it be more widely used than at present.

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