It's been known for more than 2000 years that some people with epilepsy can anticipate their seizures, by hours and sometimes even by days. This feeling of anticipation is not the same as an aura (which is in fact a partial seizure preceding the main seizure): it lasts longer and is a different feeling. Doctors call the longer anticipation feeling a prodrome.

While the causes of auras are well-understood, what causes a prodrome is not. There is considerable research interest in them because of their potential use as an early seizure warning: if they really do correspond to a physiological process that happens in the brain as part of the build-up to a seizure, then perhaps a warning device could be designed to detect them, even in those people who are not normally aware of any prodrome.

In a study published in Epilepsy Research in July, doctors from three epilepsy treatment centres in Germany investigated the frequency and nature of prodromes in 500 epilepsy out-patients using a brief questionnaire. They looked for warning feelings lasting longer than 30 minutes before the seizure, but different from any subsequent aura.

Of the patients with focal epilepsy, 6.5% reported definite prodromes, as did 4.9% of patients with idiopathic generalised epilepsy. The most common symptoms of prodromes were restlessness, headaches, malaise, feeling sick, being unable to concentrate, dizziness, and tiredness. Over half the patients with focal epilepsy who reported having prodromes also experienced auras. In most patients, there was a typical pattern of symptoms in their prodrome. The average warning time before the seizure was an hour and a half.

This is a lower percentage of patients reporting prodromes than previous studies had found. For example, in one study of mostly focal epilepsy patients, 29% reported prodromes. However other studies used a less exclusive definition of a prodrome. The current study also found a much lower rate of patients reporting emotional or psychological changes as part of a prodrome, including irritability or depression. This may be due to the use of questionnaires rather than interviews in the study: patients may not be as self-aware of this sort of symptom.

The researchers, led by Dr Andreas Schultze-Bonhage, commented that it is a shame that although prodromes have been known to exist since the beginning of the modern era of epilepsy treatment, they have not been much studied. The fact that they occur in both focal and generalised epilepsy types may indicate they are a symptom of an underlying brain mechanism that has not yet been worked out. They certainly deserve more study.