Clinical correlates and electroencephalographic features of FIRDA in a tertiary center

We aimed to explore the diagnostic value, clinical correlates and electroencephalographic features of FIRDA (Frontal intermittent rhythmic delta activity).

We retrospectively reviewed reports from EEG studies done in adults at our tertiary center between January 2015 and May 2018. For cases demonstrating FIRDA, medical files were reviewed and each case was given a diagnostic category. EEG recordings were reviewed and electrophysiologic data were extracted including FIRDA characteristics (frequency, location, duration, and symmetry). Then, a statistical analysis was done to evaluate the relationship between the diagnostic categories and EEG variables.

Ninety-four cases of FIRDA were found, with a frequency of 1.6% among inpatients. EEG recordings were available for review in 84 cases. FIRDA was asymmetric in 43 of these cases (49%), usually more prominent on the left (36/43, 84%). The diagnostic category groups included epilepsy (n = 39, 41%), other central nervous system (CNS) disease (n = 33, 35%), and systemic illness (n = 22, 23%). A significant difference in FIRDA location was found, as patients with epilepsy or other CNS disease, had a significantly higher probability for the delta activity to involve the temporal areas (frontotemporal location in 27/64 in these groups compared with 3/20 in the systemic illness group, P-value = .033).

This study provides insights to the diagnosis underlying FIRDA, especially the high rate of epilepsy patients, and calls for further neurologic investigation of cases in which FIRDA involves the temporal areas since most of these cases were due to epilepsy or other CNS disease and not a systemic illness.