Herpes simplex virus (HSV) type 1 is the most common cause of sporadic encephalitis.  Patients usually present with acute-onset fever, headache, altered mental status, and focal neurologic deficits or seizure.  MRI classically shows temporal lobe edema because the virus enters the brain via the olfactory tract and travels to the olfactory cortex (located in the medial temporal lobe).  Most patients have a "viral pattern" on cerebrospinal fluid (CSF) analysis with lymphocytic pleocytosis, normal glucose, and normal to slightly elevated protein.  Hemorrhagic inflammation of the temporal lobes also usually causes elevated erythrocytes in the CSF.

(Choice A)  Trauma from inserting the lumbar puncture needle can lead to a "traumatic tap," which is characterized by CSF evidence of normal glucose, elevated protein, and elevated erythrocytes.

(Choice B)  Bacterial meningitis is usually associated with CSF evidence of low glucose, high protein, and a markedly elevated white blood cell count with a neutrophil predominance.  Bacterial meningitis classically causes the triad of fever, neck stiffness, and altered mental state.  The presence of temporal lobe swelling on brain imaging makes HSV encephalitis far more likely than bacterial meningitis.

(Choice D)  Tuberculous or fungal meningitis is often associated with CSF evidence of low glucose, moderately elevated protein, and lymphocytic pleocytosis.  Most patients with herpes encephalitis have normal CSF glucose and elevated CSF erythrocytes.  In addition, the presence of temporal lobe swelling makes HSV encephalitis more likely than tuberculous or fungal meningitis.

(Choice E)  Patients with Guillain-Barré syndrome (GBS) often have CSF protein elevations with normal cell counts (albuminocytologic dissociation), which is thought to be due to increased permeability of the blood-nerve-barrier at the level of the nerve root.  GBS usually presents with progressive, symmetric ascending muscle weakness, not seizures and fevers.

Educational objective:
Viral infections of the central nervous system are usually characterized by an elevated white blood cell count with a lymphocytic predominance, normal glucose, and elevated (or normal) protein.  Patients with herpes encephalitis also usually have elevated erythrocytes in the cerebrospinal fluid due to hemorrhagic inflammation of the temporal lobes.  Herpes encephalitis often presents with acute fever, headache, confusion, focal neurologic deficits, and/or seizure.