What is a characteristic finding in the cerebrospinal fluid (CSF) of a patient with herpes encephalitis?

In herpes encephalitis, a characteristic finding in the cerebrospinal fluid (CSF) is the presence of markedly elevated red blood cells. This can occur due to the necrotizing nature of the infection, leading to hemorrhagic changes in the affected areas of the brain. The inflammatory response associated with herpes simplex virus infection can also lead to the rupture of blood vessels, resulting in the release of red blood cells into the CSF. This finding is significant as it helps to differentiate herpes encephalitis from other types of encephalitis or central nervous system infections, which may present with different cellular profiles and characteristics in the CSF.

While elevated neutrophils can be seen in bacterial infections, low glucose levels are typically associated with bacterial meningitis rather than herpes encephalitis. Furthermore, the lymphocyte count in herpes encephalitis usually shows an increase, rather than a decrease. Therefore, the presence of markedly elevated red blood cells is a distinctive feature that supports the diagnosis of herpes encephalitis.