Causes of epilepsy that could be defined, with a fair degree of confidence, in each of two studies. The way in which the subjects were selected was different in each study, but the final
figure—the proportion in which a cause for epilepsy could be defined—varied within narrow limits, between only 34.5 per cent and 39.0 per cent.
The fact that 61.0-65.5 per cent of people with epilepsy have no discernible cause for their seizures certainly does not mean that the remainder have ‘idiopathic’ epilepsy. Since the advent of magnetic resonance imaging we know that a large proportion of subjects with such ‘cryptogenic’ epilepsy (epilepsy of hidden cause), have minor structural changes in the
brain—very commonly zones of atrophy in one or other temporal lobe. More recent studies show that nearly 90 per cent of those with temporal lobe epilepsy, for example, will have abnormalities on magnetic resonance imaging, though these abnormalities may be very minor, and only detectable with careful measurements on the scan.
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