To identify the incidence and clinical significance of electroencephalogram (EEG) abnormalities in patients with atraumatic convexity subarachnoid hemorrhage (cSAH).  

Atraumatic cSAH presents with seizures in 6-30% of cases. Seizures are commonly reported in cerebral venous sinus thrombosis (cVST), occasionally in cerebral amyloid angiopathy (CAA), and less commonly in reversible cerebral vasoconstriction syndrome (RCVS).  EEG is often employed in the workup, but it is unclear to what degree abnormalities can be attributed to cortical injury versus epileptogenic focus. 

We retrospectively studied clinical, EEG, and imaging data of patients with acute cSAH who underwent EEG.  EEG was interpreted by a board-certified epileptologist. 

Of 26 patients with cSAH undergoing EEG, 6 presented with seizure, 9 presented with encephalopathy, 11 presented with focal neurologic deficit, and 3 presented with headache.  CAA was the most common etiology and the most common location of cSAH was frontal. 5 patients had a history of epilepsy.  The majority of EEGs were abnormal, with only 3 patients having a normal EEG.  In 8 patients, a clinical event was captured.  Abnormalities included focal slowing (14), generalized slowing (10), and epileptiform discharges (7).  18 patients had a seizure at any point from presentation to follow-up visit; 4 had status epilepticus. Most patients (20) were discharged on an anti epileptic drug (AED), with 6 patients discharged on multiple AEDs.  At follow-up, 14 patients remained on AED.