Epidemiology of epilepsy in Tasmania : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Epidemiology at Massey University, Wellington, New Zealand
Year: 2008
Type: dissertation
Study design: Observational Study
Abstract: Background \nBetter understanding of the demographic distribution of epilepsy and the prevalence of \n'more specific forms of epilepsy' in community-based settings would improve our \nunderstanding of this disorder at the population level . Although we now have good \nestimates of epilepsy prevalence for most countries, we still lack knowledge on its \ndemographic distribution by age, ethnicity, region, and socioeconomic status. In addition, \nno studies to date have reported the prevalence of epilepsy syndromes using patient \ninterview outside a hospital setting. This thesis provides the first community-based \nestimates of the prevalence of the most common clinical group of epilepsies presumed to \nhave a genetic basis - The Idiopathic Generalised Epilepsies (IGE) - by patient and \nwitness interview. \nMethods \nThis thesis has involved conducting five pieces of new research: (i) a series of reviews \nand analyses of descriptive data on epilepsy prevalence, particularly focusing on the \ncritical methodological issues of ascertainment, diagnosis and classification of epilepsy \nfor epidemiological purposes; (ii) the validation of a modified diagnostic epilepsy \nquestionnaire adapted for administration in population studies; (iii) recruitment of a \ncommunity-based cohort - The Tasmanian Epilepsy Register (TER) - through the \nAustralian national prescription database; (iv) estimation of the overall prevalence and \ndistribution of self-reported treated epilepsy in Tasmania by imputation methods; (v) \nestimation of the prevalence and distribution of IGE in Tasmania by telephone \ninterviewing. \nResults \nMy modified diagnostic questionnaire, administered by telephone interviewing and \ninterpreted with standardized guidelines, demonstrated excellent agreement with an \nepilepsy specialist's clinical assessment in diagnosing the presence of epilepsy (K = 0.94), \nseizure-onset types (K = 0.84), simple or complex partial seizures (K=0. 87), any \ngeneralized non-convulsive seizure (K=0.82), and IGE (K = 0.82). A lthough stil l \nsubstantial, agreement was not as close for secondarily general ized seizures (K = 0.74), \nand generalized tonic-clonic seizures (K = 0.79). \n7541 patients treated with antiepileptic drugs (AEDs) in the preceding year in Tasman ia \nwere eligible for recruitment through the Australian national prescription database. After \nthree mail contacts, 54.0% responded, with 43.6% who indicated treatment for epilepsy \nrepresenting 86.0% of total possible epilepsy cases by imputation (n=2063) in Tasmania. \n1180 agreed to participate in the TER, 90.0% of participants received their AEDs either \nexclusively from their general practitioner (70.9%) or in combination with a medical \nspecialist (19.1%) in the preceding twelve months. The adjusted treated epilepsy \nprevalence was 4.36 per 1000 (95% CI 4.34, 4.39); this was: lower in women (prevalence \nratio 0.92 (95% CI 0.84, 1.00); greater with increasing age (p< 0.001 ); similar in the three \nmain geographical regions; and similar by categories of socioeconomic status based on \npostcode of residence. \nFollowing enrolment, 959/1083 (88.6%) eligible TER participants completed the \ndiagnostic telephone interviewing, with partial epilepsy classified in two thirds, and \ngeneralised epilepsy in slightly more than one-fifth. IGE was observed in 20.3%, with \ntonic-clonic seizures (17.03%) and the absence epilepsies combined (11.01 %) being the \nmost common IGE seizure types and syndromes respectively. The estimated prevalence \nof IGE was 0.89 per 1000; is highest between the ages of 20-39 years and in females, but \nwas similar between Tasmanian regions and socio-economic groups. IGE prevalence \nbeyond childhood related to refractory childhood or adolescent disease rather than olderonset \ncases, and was characterised by the presence of myoclonic and tonic-clonic \nseizures. Generalised seizures, but not IGE, were less prevalent in southern Tasmania. \nConclusions \nUtilising the design approach described in this thesis may provide an alternative to \nneurological assessment, and when coupled with case ascertainment through prescription \ndata, can provide a valid estimate of the prevalence of 'more specific forms of epilepsy' \nin countries with high access to health services. The observed pattern of high elderly \nepilepsy prevalence, is similar to patterns in recent studies in other developed countries, \nand has important implications for future planning of health services in these countries. \nIGE represents a considerable proportion of community-treated disease with important \naetiological and prognostic determinants occurring at the seizure rather than syndrome \nlevel of classification.
Author: Wendyl D’Souza
Language: English
Subfield: Clinical Neurology
Field: Medicine
Domain: Health Sciences
Open Access status: green
Funders: Pfizer, St Vincent's Hospital Melbourne
OpenAlex ID: W56849661