Continuous Electroencephalogram as a Biomarker of Disease Progression and Severity in Herpes Simplex Virus-1 Encephalitis.

. Herpes simplex virus encephalitis (HSE) is the most common cause of sporadic fatal encephalitis worldwide and remains a devastating disease despite antiviral therapy. EEG can be an important tool in the diagnosis of HSE, and we propose that it can be used to monitor the progression of the disease in patients with treatment refractory HSE. . This is a case report of a patient with HSE who was monitored on continuous EEG (CEEG) throughout course of her disease. . A 62-year-old woman with no history of neurologic disease, who presented with generalized weakness and lethargy for 2 weeks, and rapidly deteriorated with encephalopathy, fever, and seizures. Lumbar puncture demonstrated elevated protein and white blood cells with positive herpes simplex virus (HSV) DNA. CEEG initially showed right-sided lateralized periodic discharges and focal seizures/status epilepticus with shifting predominance, and then later progressed to be more focal on the left, and then progressed to demonstrating more generalized findings. Magnetic resonance imaging obtained 3 times confirmed what CEEG heralded with evolution from prior studies which were concordant with CEEG, suggesting disease spread. . We report the case of a patient with HSE who was monitored on CEEG and propose that CEEG can be used as a marker for progression of disease and thus may prompt escalation in therapy. While imaging studies may confirm spread of disease, using CEEG may prevent the delay of treatment and lead to more rapid therapy in cases of refractory HSE.