Neurodegenerative disease is associated with increased incidence of epilepsy: a population based study of older adults

Objective: To determine the incidence of epilepsy among Medicare beneficiaries with a new diagnosis of Alzheimer dementia (AD) or Parkinson disease (PD). Methods: Retrospective cohort study of Medicare beneficiaries with an incident diagnosis of AD or PD in the year 2009. The 5-year incidence of epilepsy was examined by sociodemographic characteristics, comorbidities and neurodegenerative disease status. Cox regression models examined the association of neurodegenerative disease with incident epilepsy, adjusting for demographic characteristics and medical comorbidities. Results: We identified 178,593 individuals with incident AD and 104,157 individuals with incident PD among 34,054,293 Medicare beneficiaries with complete data in 2009. Epilepsy was diagnosed in 4.45% (7,956) of AD patients and 4.81% (5,010) of PD patients between 2009 and 2014, approximately twice as frequently as in the control sample. Minority race/ethnicity was associated with increased risk of incident epilepsy. Among individuals with AD and PD, stroke was associated with increased epilepsy risk. Traumatic brain injury (TBI) was associated with increased epilepsy risk for individuals with PD. Depression was also associated with incident epilepsy (AD adjusted hazard ratio (AHR): 1.23 (1.17-1.29), PD AHR: 1.45 (1.37-1.54)). In PD only, a history of hip fracture (AHR, 1.35 (1.17-1.57)) and diabetes (AHR, 1.11 (1.05-1.18) were also associated with increased risk of epilepsy. Conclusion: Incident epilepsy is more frequently diagnosed among neurodegenerative disease patients, particularly when preceded by a diagnosis of depression, TBI or stroke. Further studies into the differences in epilepsy risk between these two populations may help elucidate different mechanisms of epileptogenesis.