Encephalitis: Symptoms, Causes & Evaluation

The brain stem, cerebellum, and cerebrum are all infected by encephalitis. Encephalitis may be caused by several organisms, including HSV type 1 and arboviruses (e.g., Eastern equine encephalitis virus, Western equine encephalitis virus, St. Louis encephalitis virus, California encephalitis virus), Mycoplasma, Toxoplasma, Coccidioides, Cryptococcus, T. pallidum, Borrelia burgdorferi, Naegleria, and Mycobacterium.

CLINICAL FEATURES:

Symptoms are very similar to those of meningitis. An altered level of consciousness ranging from lethargy and irritability to frank obtundation and coma is common. Seizures and gait ataxia also occur. Personality change is generally a key factor to differentiate encephalitis from meningitis.

DIFFERENTIAL DIAGNOSES include meningitis, brain abscess, neoplasm, trauma, subdural hematoma, subarachnoid hemorrhage, systemic lupus erythematosus, toxic encephalopathy, and metabolic encephalopathy.

EVALUATION: The foundation of the diagnosis is a head CT scan and CSF analysis. The diagnosis of encephalitis is usually made by first ruling out the presence of meningitis using Gram staining, antibody titers, India ink preparations, and CSF cultures.

1. CSF analysis: A CSF sample obtained via a lumbar puncture usually shows a normal glucose level, an elevated protein level, and marked pleocytosis in patients with encephalitis, but these signs are nonspecific. When HSV or Naegleria is the causative organism, an elevated CSF red blood cell count is common. Specific CSF and blood serum titers for specific encephalitides (e.g., Toxoplasmosis) are available and useful for identifying the causative agent.

2. HSV polymerase chain reaction should be ordered when considering herpes encephalitis.

THERAPY: Because differentiating encephalitis from meningitis is very difficult, presumptive therapy should be initiated for bacterial meningitis even before the initiation of the workup. Treatment is generally supportive. HSV is treated with acyclovir with the goal of early administration.

DISPOSITION: All patients suspected of having encephalitis should be admitted to the hospital for further evaluation and treatment.