Objective:

This study explores whether seizure laterality recorded on scalp EEG is related to ictal thalamic perfusion as measured by ictal SPECT imaging.

Background:

Thalamic ictal EEG activation has been reported, but little is known about thalamic perfusion changes during seizures. 

Design/Methods:

Patients with intractable epilepsy who underwent ictal and interictal SPECT that were processed with SISCOM during presurgical epilepsy evaluation between 2021 and 2024 at Mayo Clinic Rochester were included. Seizure laterality on EEG, MRI abnormalities, and ictal and interictal SPECT including SISCOM were obtained. Thalamic SPECT signal (increased ictal uptake compared to interictal) was assessed visually in SISCOM images and categorized as unilateral left or right, bilateral, or absent. Chi-squared and Fisher’s exact tests compared categorical variables.

Results:

In total 107 patients were identified. Of these patients, 70 (65%) exhibited either unilateral or bilateral thalamic signal on SISCOM, with 30 patients having left-sided seizures and 28 having right-sided seizures on EEG. Unilateral left thalamic SPECT increased uptake was observed in 19 patients (63%) with ipsilateral EEG seizures during Neurolite injection, while unilateral right thalamic SPECT uptake was increased in 18 (64%) patients with right-sided seizures (p=0.0005). The overall predominance of the patient’s EEG seizure laterality was also associated with thalamic ictal SPECT uptake lateralization: 20 patients (60%) with predominantly left-sided seizures and 15 patients (70%) with predominantly right-sided seizures had ipsilateral thalamic increased uptake (p= 0.0004). Right-sided EEG onset seizures were significantly more likely to have no increased SPECT thalamic activity than left-sided onset seizures (p<0.05). No significant association was observed between thalamic SPECT uptake and age, injection timing, seizure duration, seizure semiology, and the presence and laterality of MRI abnormalities. 

Conclusions:

The laterality of thalamic SPECT uptake is significantly associated with seizure laterality on scalp EEG and may provide a lateralizing indicator in difficult to localize presurgical cases.