Review Question - QID 103092

This patient presents with HSV encephalitis which commonly presents as a febrile encephalopathy. CSF demonstrates normal opening pressure, elevated lymphocyte count, elevated protein, elevated RBCs, and normal glucose.

HSV-1 is a virus in the Herpesvirus family that causes HSV encephalitis, the most common cause of sporadic encephalitis in the United States. HSV encephalitis often presents as an otherwise healthy patient who presents with fever and altered mental status (encephalopathy). It should be noted that a distinguishing feature between encephalitis and meningitis is that mental status changes are very rarely seen in meningitis, as meningitis does not affect the brain parenchyma. CSF findings typical of HSV encephalitis are a normal opening pressure, elevated lymphocyte count, elevated protein, elevated RBCs, and normal glucose. Classic MRI findings are abnormalities in the temporal lobes (Figure A). Treatment consists of high-dose intravenous acyclovir. HSV encephalitis is very dangerous and without treatment has been reported to cause death in approximately 70% of cases.

Seehusen et al. review the assessment and interpretation of CSF results. They state white blood cell differential may be misleading early in the course of infection, because more than 10 percent of cases with bacterial infection will have an initial lymphocytic predominance and viral meningitis may initially be dominated by neutrophils. Culture is the gold standard for determining the causative organism in meningitis. However, polymerase chain reaction is much faster and more sensitive in some circumstances. To prove herpetic, cryptococcal, or tubercular infection, special staining techniques or collection methods may be required.

Safain et al. review the role of both medical and surgical intervention in HSV encephalitis. They state HSV encephalitis is well known to cause severe cerebral edema and hemorrhagic necrosis with resultant increases in intracranial pressure (ICP). The role of aggressive combined medical and surgical management including decompressive craniectomy and/or temporal lobectomy has shown to be beneficial in some cases as opposed to only medical therapy.

Figure A is an MRI showing temporal lobe abnormalities as is characteristic of HSV encephalitis.

Incorrect Answers:
Answer 1: C. meningitis would typically show very elevated opening pressures, decreased glucose, and no RBCs on CSF analysis. Furthermore, temporal lobe abnormalities are not commonly observed.
Answer 2: The JC virus typically causes progressive multifocal leukoencephalopathy (PML) in HIV patients. There is no evidence from the question that this patient is immunocompromised.
Answer 3: S. pneumoniae is a common cause of bacterial meningitis. However, CSF analysis of S. pneumoniae meningitis would demonstrate increased neutrophils, decreased glucose, and no RBCs.
Answer 4: N. meningitidis is a common cause of bacterial meningitis. However, CSF analysis of N. meningitidis meningitis would demonstrate increased neutrophils, decreased glucose, and no RBCs.