Epidemiology of the epilepsies.

Accurate diagnostic and case ascertainment methods are a prerequisite for epidemiological research. In epilepsy, a common problem is diagnostic accuracy as it can be diagnosed only by taking a history of the index event or by chance observation of a seizure.' The diagnosis is fundamentally a discretionary judge- ment which depends on the skill and experience of the physician and the quality of witness information available.2 Common sources of confusion are syncope or psy- chogenic attacks.'-6 As many as 10%-20% of cases referred to specialised epilepsy units with seemingly intractable seizures do not have epilepsy.' 2 4-6 Up to 30% of patients develop- ing epilepsy will eventually be classified as hav- ing chronic epilepsy.7-8 The inclusion of patients with non-epileptic attacks in the "chronic epilepsy" group may artificially inflate the proportion of chronic cases.8 By contrast, many patients with epilepsy have the condition for some time before the correct diagnosis is achieved.' 9 10 Most studies lack clear and reproducible diagnostic definitions, a recent exception being one in Ecuador." 4] It is likely, therefore, that field studies miss patients