Interictal rhythmical midline theta differentiates frontal from temporal lobe epilepsies

Abstract

SUMMARYPurpose: We evaluated the role of interictal rhythmical midline theta (RMT) in the identification of frontal lobe epilepsy (FLE) and its differentiation from temporal lobe epilepsy (TLE) and nonepileptic controls. Methods: We included 162 individuals in the study: 54 FLE patients, 54 TLE patients, and 54 nonepileptic controls. Continuous electroencephalographic (EEG)-video monitoring was performed in all individuals. Interictal RMT was included only if it occurred during definite awake states. RMT associated with drowsiness or mental activation and ictal RMT was excluded. Results: We identified RMT significantly more frequently in FLE patients (48.1%, 26 of 54) than in TLE patients (3.7%, 2 of 54) (p < 0.01), and not in the control group. The average frequency was 6 Hz (range 5-7 Hz), and the average RMT bursts lasted 8 s (3-12 s). Interestingly, all mesial FLE patients (n = 4) (as established by invasive EEG recordings) showed RMT, whereas this was less frequently the case in the other FLE patients (44%, 22 of 50) (p = 0.03). Thirteen of our 54 patients with FLE (24%) did not have any interictal epileptiform discharges (IEDs), but RMT was observed in the majority of these patients (62%, 8 of 13). Conclusion: Interictal RMT is common and has a localizing value in patients with FLE, provided that conditions such as drowsiness and mental activation as confounding factors for RMT are excluded. RMT should be included in the evaluation of patients considered for resective epilepsy surgery.

Theta EEG source localization using LORETA in partial epilepsy patients with and without medication

“…A recent study seems to support this suspicion. More or less rhythmic interictal theta activity in the frontal derivations was frequently found in patients with frontal epilepsy but rarely in temporal lobe epilepsy patients (Beleza et al, 2009). In any case, the relationship between the epileptogenic process and the activated theta network might contribute to understand the functional meaning of theta increase in PE.…”

Frontal lobe epilepsy

“…11 Interictal rhythmical midline theta (RMT) is common (50% of FLE patients) and has localizing value in patients with FLE, provided that it can be distinguished from normal variants occurring with drowsiness and mental activation tasks. 12 Ictal EEG is often generalized and localized patterns are observed in fewer than one-third of patients (Fig. 1).…”

Pearls and Oy-sters: The chapeau de gendarme sign and other localizing gems in frontal lobe epilepsy

“…More recently, a study conducted on 162 patients who underwent at least 3 days of continuous video-EEG monitoring demonstrated that interictal RMT in wakefulness was found significantly more frequently in FLE (26/54; 48.1%) compared to TLE (2/54; 3.7%) patients, and was not observed in healthy controls. 6 Therefore, when care is taken to exclude a drowsy state or mental activation, RMT serves as a useful EEG correlate of dysfunction, seen more commonly in FLE compared to TLE. It may be the only interictal abnormality seen in FLE patients, since many FLE patients lack any form of interictal epileptiform discharges.…”