Better understanding of the demographic distribution of epilepsy and the prevalence of
'more specific forms of epilepsy' in community-based settings would improve our
understanding of this disorder at the population level . Although we now have good
estimates of epilepsy prevalence for most countries, we still lack knowledge on its
demographic distribution by age, ethnicity, region, and socioeconomic status. In addition,
no studies to date have reported the prevalence of epilepsy syndromes using patient
interview outside a hospital setting. This thesis provides the first community-based
estimates of the prevalence of the most common clinical group of epilepsies presumed to
have a genetic basis - The Idiopathic Generalised Epilepsies (IGE) - by patient and
This thesis has involved conducting five pieces of new research: (i) a series of reviews
and analyses of descriptive data on epilepsy prevalence, particularly focusing on the
critical methodological issues of ascertainment, diagnosis and classification of epilepsy
for epidemiological purposes; (ii) the validation of a modified diagnostic epilepsy
questionnaire adapted for administration in population studies; (iii) recruitment of a
community-based cohort - The Tasmanian Epilepsy Register (TER) - through the
Australian national prescription database; (iv) estimation of the overall prevalence and
distribution of self-reported treated epilepsy in Tasmania by imputation methods; (v)
estimation of the prevalence and distribution of IGE in Tasmania by telephone
My modified diagnostic questionnaire, administered by telephone interviewing and
interpreted with standardized guidelines, demonstrated excellent agreement with an
epilepsy specialist's clinical assessment in diagnosing the presence of epilepsy (K = 0.94),
seizure-onset types (K = 0.84), simple or complex partial seizures (K=0. 87), any
generalized non-convulsive seizure (K=0.82), and IGE (K = 0.82). A lthough stil l
substantial, agreement was not as close for secondarily general ized seizures (K = 0.74),
and generalized tonic-clonic seizures (K = 0.79).
7541 patients treated with antiepileptic drugs (AEDs) in the preceding year in Tasman ia
were eligible for recruitment through the Australian national prescription database. After
three mail contacts, 54.0% responded, with 43.6% who indicated treatment for epilepsy
representing 86.0% of total possible epilepsy cases by imputation (n=2063) in Tasmania.
1180 agreed to participate in the TER, 90.0% of participants received their AEDs either
exclusively from their general practitioner (70.9%) or in combination with a medical
specialist (19.1%) in the preceding twelve months. The adjusted treated epilepsy
prevalence was 4.36 per 1000 (95% CI 4.34, 4.39); this was: lower in women (prevalence
ratio 0.92 (95% CI 0.84, 1.00); greater with increasing age (p< 0.001 ); similar in the three
main geographical regions; and similar by categories of socioeconomic status based on
postcode of residence.
Following enrolment, 959/1083 (88.6%) eligible TER participants completed the
diagnostic telephone interviewing, with partial epilepsy classified in two thirds, and
generalised epilepsy in slightly more than one-fifth. IGE was observed in 20.3%, with
tonic-clonic seizures (17.03%) and the absence epilepsies combined (11.01 %) being the
most common IGE seizure types and syndromes respectively. The estimated prevalence
of IGE was 0.89 per 1000; is highest between the ages of 20-39 years and in females, but
was similar between Tasmanian regions and socio-economic groups. IGE prevalence
beyond childhood related to refractory childhood or adolescent disease rather than olderonset
cases, and was characterised by the presence of myoclonic and tonic-clonic
seizures. Generalised seizures, but not IGE, were less prevalent in southern Tasmania.
Utilising the design approach described in this thesis may provide an alternative to
neurological assessment, and when coupled with case ascertainment through prescription
data, can provide a valid estimate of the prevalence of 'more specific forms of epilepsy'
in countries with high access to health services. The observed pattern of high elderly
epilepsy prevalence, is similar to patterns in recent studies in other developed countries,
and has important implications for future planning of health services in these countries.
IGE represents a considerable proportion of community-treated disease with important
aetiological and prognostic determinants occurring at the seizure rather than syndrome
level of classification.