Viral encephalitis laboratory findings

For patient information, click here Template:Encephalitis Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Encephalitis is an acute inflammation of the brain, commonly caused by a viral infection. Sometimes, encephalitis can result from a bacterial infection, such as bacterial meningitis, or it may be a complication of other infectious diseases like rabies (viral) or syphilis (bacterial). Certain parasitic or protozoal infestations, such as toxoplasmosis, malaria, or primary amoebic meningoencephalitis, can also cause encephalitis in people with compromised immune systems. Brain damage occurs as the inflamed brain pushes against the skull, and can lead to death.

Lab tests

Adult patients with encephalitis present with acute onset of fever, headache, confusion, and sometimes seizures. Younger children or infants may present with irritability, anorexia and fever. Neurological examinations usually reveal a drowsy or confused patient. Stiff neck, due to the irritation of the meninges covering the brain, indicates that the patient has either meningitis or meningeoncephalitis. Examination of the cerebrospinal fluid obtained by a lumbar puncture procedure usually reveals increased amounts of protein and white blood cells with normal glucose, though in a significant percentage of patients, the cerebrospinal fluid may be normal. CT scan often is not helpful, as cerebral abscess is uncommon. Cerebral abscess is more common in patients with meningitis than encephalitis. Bleeding is also uncommon except in patients with herpes simplex type 1 encephalitis. Magnetic resonance imaging offers better resolution. In patients with herpes simplex encephalitis, electroencephalograph may show sharp waves in one or both of the temporal lobes. Lumbar puncture procedure is performed only after the possibility of prominent brain swelling is excluded by a CT scan examination. Diagnosis is often made with detection of antibodies against specific viral agent (such as herpes simplex virus) or by polymerase chain reaction that amplifies the RNA or DNA of the virus responsible.

Diagnosis

An examination may show:

• Abnormal reflexes
• Increased intracranial pressure
• Mental confusion
• Mouth ulcers
• Muscle weakness
• Neck stiffness
• Signs in other organs, such as the liver and lungs
• Skin rash
• Speech problems

Tests may include:

• Brain MRI
• CT scan of the head
• Culture of cerebrospinal fluid (CSF), blood, or urine (however, this test is rarely useful)
• Electroencephalogram (EEG)
• Lumbar puncture and CSF examination
• Tests that detect antibodies to a virus (serology tests)
• Test that detects tiny amounts of virus DNA (polymerase chain reaction -- PCR)