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CDHB

Encephalitis

Clinical Features

• These usually include fever, meningism and signs of cerebral dysfunction such as altered conscious level/confusion, seizures, myoclonus, papilloedema or focal signs such as aphasia or weakness.

Causes

• Viral
  • Herpes Simplex Virus (HSV) - this is the most urgent to identify as it requires immediate therapy. It often produces a rapid onset illness with little prodrome. Cutaneous herpetic lesions are uncommon.
  • Endemic viruses - mumps, measles, rubella, chickenpox, adenovirus, enteroviruses, EBV, CMV, HIV.
  • Travel-related infecting agents - many severe viral and other encephalitides are transmitted by biting insects.
• Post Viral: One of the most common causes. MRI shows diffuse, predominantly white matter changes.
• Non-Viral: Bacterial endocarditis, TB, syphilis, listeria, cat scratch, malaria, nocardia (with or without abscess), toxoplasmosis.

Investigations

Important differential diagnoses include meningitis, severe sepsis, cerebral neoplasia, SLE, toxic metabolic encephalopathy (see Stupor and Coma).

• MRI brain scan - to help establish a diagnosis of either post viral or HSV encephalitis and to exclude other diseases mimicking encephalitis.
• CSF exam (provided no contraindication on brain scan) - routine culture (viruses, TB, bacteria and fungi), biochemistry and microscopy. Cell counts almost always show lymphocytic pleocytosis. A normal result casts some doubt on the diagnosis of encephalitis. An additional 0.5 mL CSF is required for HSV culture and PCR.
• CBC + diff, Na, K, Ca, glucose, urea, creatinine, AST, ALT, GGT, ALP, bili.
• Blood cultures, throat swabs (bacteria and viruses), stool culture for viruses, serum for storage, serology for EBV, CMV, HIV.
• CXR.
• EEG - this is not specific but is almost always abnormal in encephalitis. The finding of periodic complexes may be of more specific help when HSV is suspected.

Treatment

• If HSV suspected treatment is urgent. Give aciclovir 10 mg/kg IV q8h. Consult Infectious Diseases regarding duration of aciclovir treatment (often 14 days). Adjust dose for reduced renal function. Prognosis correlates with level of consciousness at commencement of therapy.
• Steroids may be appropriate for selected cases of either herpetic or non-herpetic encephalitis particularly if there is evidence of raised intracranial pressure.
• Anticonvulsant therapy will be necessary in some patients.
• Close neurological observation to detect signs of increasing intracranial pressure.

Topic Code: 1531