Electrographic Seizures in Patients with Acute Encephalitis

Clinical seizures and status epilepticus are frequent complications of encephalitis, can lead to depressed level of consciousness, and are associated with poor outcome. We sought to determine the frequency, risk factors, and clinical impact of electrographic seizures detected with continuing electroencephalography (cEEG) in patients with encephalitis and altered level of consciousness.

We retrospectively identified all patients with presumed or definite viral or autoimmune encephalitis who underwent cEEG monitoring at Henry Ford Hospital from January 2012 to October 2017. Clinical data and cEEG monitoring reports were abstracted and recorded. The primary outcome was electrographic seizures detected by cEEG.

Of 1,735 patients who underwent a minimum of 12 h of cEEG monitoring, we identified 54 with a verified discharge diagnosis of encephalitis. Twenty-two of these patients (41%) had electrographic seizures on cEEG. Compared with encephalitis patients without seizures, electrographic seizures were associated with lower serum sodium levels (137 ± 5 vs 141 ± 7, P = 0.027) and more often were on antiepileptic therapy (100% vs 78%, P = 0.033) on the first day of monitoring. Seizures were also associated with a higher frequency of cortical imaging abnormalities (68% vs 28%, P = 0.005), lateralized periodic discharges (LPDs; 50% vs 16%, P = 0.014), delta background frequency (81% vs 45%, P = 0.010), low or suppressed voltage (96% vs 62%, P = 0.005), and focal slowing (86% vs 47%, P = 0.004). There was no association between electrographic seizures and clinical outcome at discharge.

Electrographic seizures occur in approximately 40% of patients with acute encephalitis. Low serum sodium, cortical imaging abnormalities, and on cEEG LPDs and background abnormalities are associated factors. The lack of association with short-term outcome suggests that with aggressive treatment, the clinical impact of electrographic seizures in encephalitis can be minimized.