Interictal spiking in adult newly-diagnosed focal epilepsy of unknown cause: The effect of age

•Elderly subjects with recent-onset, non-symptomatic focal epilepsy show a significant propensity to express interictal epileptiform abnormalities mainly during NREM 3–4 sleep.•Age per se seems to affect this peculiar spiking pattern.•This observation might be useful when choosing EEG recording procedures in the presence of suspected recent-onset focal epileptic seizures.

ObjectiveTo assess the yield of interictal EEG spiking in standard and whole-night sleep EEGs in elderly subjects with recent-onset focal seizures compared to younger patients.MethodsDetection of interictal epileptiform abnormalities (IEAs) and rating of mean spike index (number of interictal discharges/minute) values for different sleep stages (NREM stages 1–2 and 3–4 and REM sleep) in standard EEG (S-EEG) and 24-h ambulatory EEG (A-EEG) at first referral in three groups of thirty consecutive outpatients [aged 20–39 (young), 40–59 (adults) and ⩾60 years (elderly)], retrospectively selected according to a subsequent diagnosis of focal epilepsy of unknown cause, no sleep disorders or drugs or comorbidities affecting sleep and EEG.ResultsElderly subjects showed a lower rate of IEAs on S-EEG (p < 0.01) but a higher propensity for spiking during deep NREM sleep, 11/30 showing IEAs exclusively during stages 3–4. Mean spike index showed a significant increase in IEAs between sleep stages 1–2 and 3–4 in the elderly subjects (p < 0.001).ConclusionsA significant association emerged between IEAs during deep sleep and age (p < 0.001).SignificanceEEG recordings covering deep NREM sleep should be recommended when IEAs detection is needed to support a diagnosis of epilepsy in elderly subjects.