To determine the incidence of epilepsy among Medicare beneficiaries with a new diagnosis of Alzheimer dementia or Parkinson disease.

Neurodegenerative diseases are characterized by cell death and disruption of brain architecture, which can lead to the development of epilepsy. There is, however, limited data on the burden of epilepsy among neurodegenerative disease populations.

Retrospective cohort study of Medicare beneficiaries with an incident diagnosis of Alzheimer disease (AD) or Parkinson disease (PD) in the year 2009.  The 5-year incidence of epilepsy was then examined by demographic characteristics and neurodegenerative disease status. Regression models were built to examine the association of neurodegenerative disease with incident epilepsy, adjusting for demographic characteristics.

We identified 421,240 individuals with incident AD, and 114, 201 individuals with incident PD among 42,931,475 Medicare beneficiaries with complete data in 2009.  Epilepsy was diagnosed in 2.13% (n=8,976) of AD patients and 2.01% (n=2382) of PD patients between 2009 and 2014, which is lower than simultaneously observed in the general Medicare sample (2.7%, n=1,137,957).  Among PD patients, a slightly greater odds of incident epilepsy were associated with female sex (AOR 1.07, 1.02-1.12); there were no associations between incident epilepsy and race/ethnicity. Among AD patients, blacks had a greater odds of incident epilepsy (AOR 1.62, 1.14-2.3) as compared to whites, and women had slightly lower odds of incident epilepsy (AOR 0.94, 0.91- 0.96). Unlike in the general Medicare population, incident epilepsy was not positively associated with increasing age, and was not negatively associated with Asian race in either PD or AD.

New onset epilepsy is uncommon among newly diagnosed neurodegenerative disease patients. Interestingly, epilepsy incidence in neurodegenerative disease does not follow the demographic variations in epilepsy risk observed in the general Medicare population. Further study into the differences in epilepsy risk between these two populations may help elucidate different mechanisms of epileptogenesis.