American Board of Psychiatry and Neurology (ABPN) Practice Exam 2026 - Free ABPN Practice Questions and Study Guide

In cases of suspected herpes simplex encephalitis (HSE), cerebrospinal fluid (CSF) analysis is considered the most significant diagnostic test. This is primarily because HSE often leads to specific changes in the CSF, including an elevated white blood cell count, a predominance of lymphocytes, and elevated protein levels. Additionally, polymerase chain reaction (PCR) testing of the CSF can directly detect the presence of herpes simplex virus (HSV) DNA, which is both sensitive and specific for HSE.

While cranial MRI is useful and can show characteristic findings such as unilateral or bilateral temporal lobe abnormalities, it does not definitively confirm the presence of the virus. Electroencephalogram (EEG) might demonstrate encephalopathic changes associated with HSE but is not specific for diagnosing the condition. Blood tests may help rule out other causes or provide background information but do not confirm an HSE diagnosis. Thus, CSF analysis, particularly with PCR testing, is critical in making an accurate diagnosis of herpes simplex encephalitis.