[Use of drug reimbursement as markers of disease for epidemiological and cost analysis: The case of severe epilepsy in France]

Abstract

Objectives: Population characteristics of epileptic patients remain poorly documented in France. Health Insurance claims database may be useful to perform cost and epidemiological studies provided that patients' diagnosis could be identified especially through drugs used as markers. This study explored the possibility to use the French Sickness Fund (FSF) database to determine the prevalence and direct cost of epilepsy.

Method: The "FSF" reimbursement database is a 1/97 representative sample of the population covered under the French General Scheme. Only the fraction of patients fully covered for epilepsy may be identified by a diagnosis in the database. Others can only be identified through their claims for antiepileptic drugs (AEDs) with the limitation that, among the 19 AEDs used, some are not specific for epilepsy. An algorithm was built to select patients to get a range of prevalence estimates whereas medical expenses of patients were derived on the fully covered sub-population.

Results: Only patients treated in polytherapy (≥2 AEDs) were deemed to be identified in a relevant way by an algorithm based on drug usage. The prevalence of epilepsy in this sub-group in 2009 was estimated between 1.83 and 2.79‰ (93,000-142,000 patients). A proportion of 70.1 to 71.6% were fully covered for their expenses, with epilepsy alone as a cause in only 27 to 33% of them. The most frequent other co-morbidities were psychiatric disorders and invalidating stroke. The annual per capita expenses were in the range 6.696-6.601€ in patients in polytherapy. Inpatient care and drug costs represented about 50 and 27% of overall expenses, respectively. The increase by 24.4% of polytherapy patients mean costs as compared to monotherapy raised to 72% (IC 95: 44-106%) after adjustment for age, gender and presence of severe co-morbidity.

Conclusion: In France, in 2009, 93,000 to 142,000 epileptic patients have been treated for epilepsy with a polytherapy. About one out of three patients only benefited from a full coverage of their medical expenses for epilepsy but half of them were fully covered for another disease. This resulted from the frequent presence of a severe co-morbidity especially psychiatric or due to a history of an invalidating stroke. Conversely, about 30% of epileptic patients in polytherapy, fully eligible to a full coverage did not benefit from it, which suggested an important sub-declaration of severe epilepsy.