, with implications for diagnosis and patient care. The findings “strongly support previous observations of a bidirectional association between these two brain disorders,” said Eva Bølling-Ladegaard, MD, a PhD student, department of clinical medicine (Neurology), Aarhus (Denmark) University.
“We add to the existing evidence in temporal range, showing that the increased risks of depression following epilepsy, and vice versa, are sustained over a much more extended time period than previously shown; that is, 20 years on both sides of receiving a diagnosis of the index disorder,” Ms. Bølling-Ladegaard said.
The study was published online in Neurology.
Epilepsy then depression
The researchers examined the magnitude and long-term temporal association between epilepsy and depression. They compared the risk of the two brain disorders following another chronic disorder (asthma) in a nationwide, register-based, matched cohort study.
In a population of more than 8.7 million people, they identified 139,014 persons with epilepsy (54% males; median age at diagnosis, 43 years), 219,990 with depression (37% males; median age at diagnosis, 43 years), and 358,821 with asthma (49% males; median age at diagnosis, 29 years).
The rate of developing depression was increased nearly twofold among people with epilepsy compared with the matched population who did not have epilepsy (adjusted hazard ratio, 1.88; 95% confidence interval, 1.82-1.95).
The rate of depression was highest during the first months and years after epilepsy diagnosis. It declined over time, yet remained significantly elevated throughout the 20+ years of observation.
The cumulative incidence of depression at 5 and 35 years’ follow-up in the epilepsy cohort was 1.37% and 6.05%, respectively, compared with 0.59% and 3.92% in the reference population.
The highest rate of depression after epilepsy was among individuals aged 40-59 years, and the lowest was among those aged 0-19 years at first epilepsy diagnosis.
Depression then epilepsy
The rate of developing epilepsy was increased more than twofold among patients with incident depression compared with the matched population who were without depression (aHR, 2.35; 95% CI, 2.25-2.44).
As in the opposite analysis, the rate of epilepsy was highest during the first months and years after depression diagnosis and declined over time.
The cumulative incidence of epilepsy at 5 and 35 years after depression diagnosis was 1.10% and 4.19%, respectively, compared with 0.32% and 2.06% in the reference population.
The rate of epilepsy was highest among those aged 0-19 years at time of first depression diagnosis and was lowest among those aged 80+ at first depression diagnosis.
For comparison, after asthma diagnosis, rates of depression and epilepsy were increased 1.63-fold (95% CI, 1.59-1.67) and 1.48-fold (95% CI, 1.44-1.53), respectively, compared with matched individuals without asthma.
Using admission with seizures as a proxy for treatment failure, the researchers observed an increased risk of treatment failure among people with epilepsy who were diagnosed with depression.
“Our results support previous findings indicating worse seizure outcomes in people with epilepsy and coexisting depression,” said Ms. Bølling-Ladegaard.
“Increased clinical awareness of the association between epilepsy and depression is therefore needed in order to increase the proportion of patients that receive appropriate treatment and improve outcomes for these patient groups,” she said.