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Abstract

Major depression has been shown to increase the risk for development of epilepsy, but prior studies have not evaluated whether this is due to specific symptoms of depression. We conducted a population-based case–control study of all newly diagnosed unprovoked seizures among Icelandic children and adults aged 10 years and older to test the hypothesis that major depression is a risk factor for developing unprovoked seizure and epilepsy, and to address whether specific symptoms of depression account for this increased risk. Cases were matched to the next two same sex births from the population registry. Using standardized interviews, we ascertained symptoms of major depression to make a Diagnostic and Statistical Manual, Fourth Edition (DSM-IV) diagnosis. A history of major depression was 1.7-fold more common among cases than among controls (95% confidence interval, 1.1–2.7). A history of attempted suicide was 5.1-fold more common among cases than among controls (95% confidence interval, 2.2–11.5). Attempted suicide increased seizure risk even after adjusting for age, sex, cumulative alcohol intake, and major depression or number of symptoms of depression. Major depression and attempted suicide independently increase the risk for unprovoked seizure. These data suggest that depression and suicide attempt may be due to different underlying neurochemical pathways, each of which is important in the development of epilepsy. Ann Neurol 2005