Association between Subclinical Epileptiform Discharge and the Severity of Cognitive Decline in Alzheimer's Disease: A Longitudinal Cohort Study

Background: Alzheimer's disease (AD) is the most common type of dementia. Aging is a risk factor for both AD and seizures. Subclinical epileptiform discharge (SED) has no evident clinical manifestation in patients with AD. Therefore, SED is liable to be overlooked in these patients since electroencephalography is not routinely performed in clinical settings. Previous studies about the association between SED and AD have yielded inconsistent results. Objective: The current study aimed to evaluate the prevalence of SED and its effect on AD severity and clinical outcomes. Methods: Patients with AD from Kaohsiung Municipal Ta-tung Hospital were included in this study. International 10-20 system scalp electroencephalography for 13 minutes was performed to detect SED. Clinical outcomes of patients with and without SED were assessed by neuropsychological tests [Cognitive Abilities Screening Instrument (CASI), Mini-Mental State Examination (MMSE), and Clinical Dementia Rating Scale Sum of Boxes (CDR-SOB)]. Results: 288 patients (mean age 80.5 years, 60.4% female) were enrolled in this study. Fifty-seven (19.8%) out of 288 patients with AD had SED. The prevalence of SED increased with the severity of cognitive impairment. Compared with patients without SED, those with SED showed significantly greater decline in CASI (-9.32 versus -3.52 points, p = 0.0001) and MMSE (-2.52 versus -1.12 points, p = 0.0042) scores in one year. Conclusion: SED may play a significant role in AD progression and is a potential therapeutic target.