Brief asymmetric tonic posturing with diffuse low-voltage fast activity in seizures arising from the mesial parietal...

Seizures originating from the parietal lobe can demonstrate variable semiology. Our aim was to describe the electroclinical features of seizures originating from the mesial parietal lobe.

We identified four patients through the Comprehensive Epilepsy Program at our institution, who had strong evidence of a mesial parietal source for their epilepsy, including a mesial parietal structural lesion.

Patients had very frequent brief seizures despite anticonvulsants, each lasting 10-30s, with rapid return of awareness post-event. Clinically attacks were bland, or showed asymmetric tonic posturing, often with partially preserved awareness. Ictal EEG showed diffuse low voltage fast activity.

Seizures arising from the precuneus, in the mesial parietal lobe, appear to have a recognizable electroclinical phenotype. Although the clinical and EEG features might have been considered 'non-localizing', there is a striking similarity across patients. The precuneus is a key component of the default mode network (DMN), important for internal reflective thinking. Deactivation of this region has been found to be a prominent feature of generalized spike and wave epileptiform activity. The seizure semiology of these patients presumably reflects activation of this region, and ictal propagation along intrinsically connected components of the DMN.