PURPOSE: Patients with Alzheimer's dementia (AD) who do not have a history of epilepsy have a higher frequency of subclinical epileptiform discharge (SED) than healthy individuals. This meta-analysis aims to investigate the frequency of SED in patients with AD using different EEG protocols and to compare SED rates between early- and late-onset AD. METHODS: This study adhered to the Preferred Reporting Items for Systematic Reviews and Meta-analysis guidelines. We searched various databases until January 2024 for studies reporting the frequency of SED in patients with AD who did not have a history of epilepsy. A meta-analysis was conducted using a random-effects model. RESULTS: Thirteen studies involving 1,373 patients with AD were analyzed. The patients had a mean age of 71.2 years, and 59.3% were women. The pooled SED rate was found to be 18.3%. The SED rate was higher with extended EEG protocols (26.7%) than with routine EEG protocols (12.1%). It was also observed that patients with early-onset AD had higher SED rates with routine EEG protocols (14.4%) and extended EEG protocols (43.9%) than those with late-onset AD (10.5 and 21.3%, respectively). Furthermore, patients with AD had a 3.55 relative risk (P <
0.001) of SED compared with healthy controls. Specifically, patients with early-onset AD showed a significantly higher risk of developing SED than those with late-onset AD (relative risk, 4.48
P <
0.001). CONCLUSIONS: Subclinical epileptiform discharge frequency was high in patients with AD, particularly in those with early onset AD.