Epilepsy is an extremely difficult condition to diagnose. There's no blood test for it; EEG tests (electroencephalography, which measures the spontaneous electrical activity in the brain) can't always detect it. The only sign is repeated unprovoked seizures, and even these can be mimicked by other conditions. Science has long been searching for a single defined feature of epileptic seizures that could reliably identify the presence of epilepsy.

In a presentation at the American Epilepsy Society congress in San Diego in December, Professor Jerome Engel reported a promising new biomarker for epilepsy: fast ripples. These are features visible on EEG: they are very short, very high-frequency wobbles in electrical output from deep in the brain, which happen between seizures. They were first reported in 1999.

Currently, when interpreting EEGs, doctors look for particular patterns of electrical activity in the brain which tend to be typical of epilepsy (though they can also be present in EEGs of people who do not have epilepsy). In particular, "spike-and-wave" patterns are indicative, but they don't provide any information about where seizures start in the brain.

Fast ripples have now been investigated in both animals and humans. Their appearance appears to be proportional to the severity of epilepsy and they can also be used to predict whether epilepsy will develop after traumatic brain injury. They only occur in the area of the brain where seizures happen.

Potential uses of fast ripples are revolutionary. They include:

• an accurate diagnostic tool,
• prediction of development of epilepsy after head injury - could treatments be developed to prevent seizures starting?
• assessment of treatment efficacy much faster than by waiting to see if another seizure occurs,
• identification of candidates for epilepsy surgery,
• development of rapid screening methods to identify new AEDs.

The only difficulty with using fast ripples is that they can currently only be detected using EEG electrodes implanted into the brain, rather than glued to the scalp. Implanting electrodes is too invasive and risky a procedure to be used routinely for everybody. Magneto-encephalography (a technique related to EEG), or a combination of magnetic resonance imaging (MRI) and EEG show promise for being able to detect fast ripples non-invasively, but these techniques have not yet been perfected.

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