Ictal–interictal continuum and status epilepticus: Two sides of the same coin? A prospective magnetic resonance imaging study

Objective: Status epilepticus (SE) is the most severe expression of seizures, encompassing both SE with prominent motor symptoms and nonconvulsive SE (NCSE). Ictal–interictal continuum (IIC), an electroencephalographic phenomenon, is characterized by periodic discharges (PD), spike-and-waves or sharp-and-waves (SW), or lateralized rhythmic delta activity (LRDA). Peri-ictal magnetic resonance imaging (MRI) abnormalities (PMA) may offer a potential surrogate marker for ictal activity, yet their association with IIC remains unclear. We aimed to investigate the occurrence of PMA in patients with SE and IIC, and to determine the relationship between IIC patterns and PMA through a latent cluster analysis (LCA). Methods: In a prospective cohort study, 223 adult patients diagnosed with SE or IIC underwent electroencephalography (EEG) and MRI within 48 h of diagnosis. Patients were stratified into two groups: the IIC group and SE group. PMA were assessed using the following MRI sequences: diffusion-weighted imaging, fluid-attenuated inversion recovery, and arterial spin labeling. LCA was performed to identify classes based on etiology, EEG patterns, and their localization. Results: PMA were as frequent in patients of the IIC group (23/49, 47%) as in patients of the SE group (64/149, 43%, p =.37). In the IIC group, peri-ictal hyperperfusion was more frequently associated with lower frequency PD/SW (.5–1 Hz; 12/19, 63%), followed by LRDA (4/13, 31%) and higher frequency PD/SW (>1–2.5 Hz; 4/17, 24%). LCA revealed two classes; Class 1, characterized by nonunilateral high-frequency PD/SW and triggering factors in epilepsy, had fewer PMA (18%) as compared to Class 2, characterized by predominantly unilateral low-frequency PD/SW and diverse etiologies (50%; odds ratio = 5.79, p =.02). Significance: PMA occurrence in IIC aligned closely with that in SE, suggesting an overlap between IIC and SE and raising the critical question of whether patients with IIC may have NCSE. We propose an etiology-driven approach for EEG interpretation in IIC, which may enhance diagnostic accuracy and treatment strategies.