Late-onset epilepsy of unknown etiology is more treatment-responsive than acquired lesional late-onset epilepsy

Late-onset epilepsy of unknown etiology (LOEU) carries an elevated risk of dementia, suggesting that it may represent an early manifestation of neurodegenerative or cerebrovascular disease. Direct comparisons between LOEU and acquired lesional late-onset epilepsy (LOE) may elucidate clinical features specific to LOEU.

We performed a retrospective chart review of patients with LOE, with first documented seizure at age 55 or older, whose evaluation included an epilepsy-protocol brain MRI and/or inpatient video-EEG evaluation. Etiology was determined from neuroimaging lesions and medical history. Patients without an identified etiology were categorized as LOEU. Analyses were performed controlling for sex, age of onset, and epilepsy duration.

We identified 75 LOEU (mean onset: 64.9 years, 38.7% female) and 57 acquired lesional LOE cases with etiologies including cortical stroke, hemorrhage, neoplasm, trauma, or infection (mean onset: 66.5 years, 36.8% female). LOEU was less likely to have a history of status epilepticus (6.7% vs. 21.1%, aOR: 0.28, p < 0.03) or to have undergone inpatient video-EEG monitoring (13.3% vs. 24.6%, aOR: 0.34, p < 0.04). LOEU was prescribed fewer ASMs compared to acquired lesional LOE (aOR: 0.43, p < 0.02), and LOEU patients prescribed multiple ASMs had lower average 12-month seizure frequency than acquired lesional LOE (median: 0.2 vs. 1.0, p < 0.01). LOEU had lower rates of vascular comorbidities than acquired lesional LOE, though rates of subsequent dementia were not significantly different (5-year risk: 16.6% vs. 17.7%). An exploratory cluster analysis demonstrated an LOEU subgroup with older onset, higher prevalence of white matter hyperintensities, cerebral atrophy, epileptiform discharges, and greater epilepsy severity.

LOEU was associated with fewer proxies for epilepsy severity, signifying that LOEU is more often treatment-responsive than acquired lesional LOE. LOEU has lower rates of comorbid vascular disease compared to acquired lesional LOE, suggesting that occult cerebrovascular disease is not overrepresented in LOEU relative to other forms of LOE.

People who develop epilepsy after age 55 without a known cause usually respond well to treatment and need fewer antiseizure medications than people with epilepsy from a known brain injury. In this study, they had fewer hospital stays for seizure monitoring and fewer vascular problems. Dementia risk was high in patients with late-onset epilepsy, both when the cause was known and when it was unknown. Late-onset epilepsy without a known cause is often less severe but still needs regular monitoring for memory and thinking problems.