Nonlesional late-onset epilepsy: Semiology, EEG, cerebrospinal fluid, and seizure outcome characteristics

Incidence and prevalence of epilepsy increase with advancing age. Although the majority of late-onset epilepsies are of lesional origin, a considerable proportion of patients present with unknown etiology. The aim of this study was to evaluate the semiological, electroencephalographic (EEG), and cerebrospinal fluid (CSF) characteristics as well as the 12-month seizure outcome in a cohort of patients with nonlesional late-onset epilepsy (≥55 years).

A total of 54 patients with newly diagnosed nonlesional late-onset epilepsy (NLLOE) were retrospectively evaluated for seizure type using the most recent International League Against Epilepsy (ILAE) classification of seizure types, EEG characteristics, and CSF profile and followed-up for at least 12 months after epilepsy onset. Results were compared with a gender-matched control group of 58 patients with nonlesional early-onset epilepsy (NLEOE).

The predominant seizure types in NLLOE were focal to bilateral tonic-clonic seizures (30%) as well as focal onset impaired awareness motor seizures (IAMS) (22%) and focal onset impaired awareness nonmotor seizures (IANMS) (22%). The predominant seizure types in NLEOE were focal to bilateral tonic-clonic seizures (43%) as well as focal onset aware nonmotor seizures (ANMS) (31%) and IAMS (31%). Focal onset impaired awareness nonmotor seizures were found to be more characteristic in patients with NLLOE (p = 0.019; α < 0.05; NLLOE: 22.2% vs. NLEOE: 8.6%). Electroencephalography revealed no significant differences between groups. Of interest, three patients with NLLOE (8%) presented with oligoclonal bands (OCB) in CSF albeit absence of antineuronal antibodies. Seizure-free rate was 70%. Adverse effects from medication leading to antiepileptic drug (AED) change were reported in 12 patients (22%), valproate was the best tolerated AED in patients with NLLOE [adverse effects in 9%, compared with 12% (gabapentin) and 26% (levetiracetam)].

Using the most recent classification system, different patterns of semiological characteristics were identified: NLLOE more frequently present with IANMS, whereas patients with NLEOE rather have ANMS. Oligoclonal bands were only detected in patients with NLLOE, indicating that careful exclusion of autoimmune encephalitis in this patient group is warranted. Our findings may help to more accurately identify and characterize patients with NLLOE to improve targeted diagnostics and adequate treatment in this challenging group of patients.