Abstracts

Rationale: The long term risk for developing epilepsy in individuals is measured as the Remaining Lifetime Risk (RLTR), which is the probability that a person will develop epilepsy over their remaining lifetime. This measure considers the impact of the competing risk of dying. The lifetime risk is important for diseases like epilepsy where the incidence increases dramatically in older ages. Methods: Individuals with incident epilepsy in Rochester, Minnesota, between 1960 and 1979 identified through the records linkage system are included. Epilepsy was defined as two or more unprovoked seizures. For the calculation of RLTR, we obtained the deaths in Rochester, Minnesota, by age, gender, and calendar year. We calculated the cumulative incidence (CI) and the RLTR overall, by etiology of epilepsy and separately beginning at age 20, age 30, age 40, age 50 and age 60. Results: Among the 412 individuals with incident epilepsy diagnosed between 1/1/1960 and 12/31/1979, idiopathic/cryptogenic epilepsy predominates (64.3%), then remote symptomatic (29.1%), and then progressive symptomatic (6.6%). CI is 0.9% to age 20, 1.7% to age 50, and 3.4% to age 80. RLTR is 0.9% to age 20, 1.6% to age 50, and 3.0% to age 80. The curves begin to noticeably diverge at age 60 years (figure) when mortality begins to increase, demonstrating that CI overestimates RLTR when the competing risk of mortality becomes large. Relative to the RLTR, CI is the same at age 60-64, 6.6% higher at age 70-74 and 17.8% higher at age 80-84. These same trends are observed for men and for women, although the risk for developing epilepsy is higher in men. Results will be presented by etiology and decade. Over the subsequent 20 years, a 20-year old will have a 0.6% RLTR for developing epilepsy. The corresponding RLTRs over a 20 year period for individuals aged 30, 40, 50, and 60 years are 0.5%, 0.5%, 0.7%, and 1.6%. Applying age- and gender-specific RLTR estimates to the July 2007 US population (301,139,947), 11,744,457 individuals will ultimately develop epilepsy in their lifetime. Conclusions: In this population-based study, one in 26 people will develop epilepsy during their lifetime. Risk is higher in men than women. Epilepsy will occur in one of every 21 males and in 1 of every 28 females. The RLTR describes the risk of developing epilepsy in individuals from their current age through their remaining lifetime, accounting for the risk of dying due to competing causes like cancer and cardiovascular diseases. This information is useful for clinicians and also for public health planning purposes, because it forecasts the burden of epilepsy in the community, of considerable importance as the population ages.