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Information ⬇

An infection of the brain parenchyma commonly associated with meningitis (“meningoencephalitis”). Clinical features are those of viral meningitis plus evidence of brain tissue involvement, commonly including altered consciousness such as behavioral changes and hallucinations; seizures; and focal neurologic findings such as aphasia, hemiparesis, involuntary movements, and cranial nerve deficits.

Etiology !!navigator!!

The same organisms responsible for viral meningitis are also responsible for encephalitis, although relative frequencies differ. The most common causes of sporadic encephalitis in immunocompetent adults are herpesviruses (HSV, VZV, EBV) (Table 191-4). HSV encephalitis should be considered when focal findings are present and when involvement of the inferomedial frontotemporal regions of the brain is likely (olfactory hallucinations, anosmia, bizarre behavior, or memory disturbance). Epidemics of encephalitis are usually caused by arboviruses. WNV has been responsible for the majority of arbovirus meningitis and encephalitis cases in the United States since 2002. Prominent motor manifestations, including acute poliomyelitis-like paralysis, may occur with WNV.

Diagnosis !!navigator!!

CSF studies are essential; typical CSF profile is similar to viral meningitis. CSF PCR tests allow for rapid and reliable diagnosis of HSV, EBV, VZV, CMV, HHV-6, and enteroviruses. CSF virus cultures are generally negative. Serologic studies also have a role for some viruses. Demonstration of WNV IgM antibodies in the CSF is diagnostic of WNV encephalitis.

MRI is the neuroimaging procedure of choice and demonstrates areas of increased T2 signal. Bitemporal and orbitofrontal areas of increased signal are seen in HSV encephalitis, but are not diagnostic (Fig. 191-2). The EEG may suggest seizures or show temporally predominant periodic spikes on a slow, low-amplitude background suggestive of HSV encephalitis.

Brain biopsy is now used only when CSF PCR studies fail to identify the cause, focal abnormalities on MRI are present, and progressive clinical deterioration occurs despite treatment with acyclovir and supportive therapy.

Differential Diagnosis !!navigator!!

Includes both infectious and noninfectious causes of encephalitis, including vascular diseases; abscess and empyema; fungal (Cryptococcus and Mucor), spirochetal (Leptospira), rickettsial, bacterial (Listeria), tuberculous, and mycoplasmal infections; tumors; toxic encephalopathy; SLE; autoimmune or paraneoplastic encephalidities, and acute disseminated encephalomyelitis.

Treatment: Viral Encephalitis

  • All pts with suspected HSV encephalitis should be treated with IV acyclovir (10 mg/kg every 8 h) while awaiting diagnostic studies.
  • Pts with a PCR-confirmed diagnosis of HSV encephalitis should receive a 14- to 21-day course of therapy. Consider repeat CSF PCR after completion of acyclovir therapy; pts with a persistently positive CSF PCR for HSV after completing a standard course of acyclovir therapy should receive additional treatment, followed by a repeat CSF PCR test.
  • Acyclovir treatment may also be of benefit in severe encephalitis due to EBV and VZV. No therapy currently available for enteroviral, mumps, or measles encephalitis.
  • IV ribavirin (15-25 mg/kg per day given in three divided doses) may benefit severe encephalitis due to California encephalitis (LaCrosse) virus.
  • CMV encephalitis should be treated with ganciclovir (5 mg/kg every 12 h IV over 1 h, followed by maintenance therapy of 5 mg/kg every day), foscarnet (60 mg/kg every 8 h IV over 1 h, followed by maintenance therapy 60-120 mg/kg per day), or a combination of the two drugs; cidofovir (5 mg/kg IV once weekly for 2 weeks, then biweekly for two or more additional doses, depending on response; prehydrate with normal saline and pretreat with probenecid) may provide an alternative for nonresponders.
  • No proven therapy is available for WNV encephalitis; small groups of pts have been treated with interferon, ribavirin, WNV-specific antisense oligonucleotides, IV immunoglobulin preparations of Israeli origin containing high-titer anti-WNV antibody, and humanized monoclonal antibodies directed against the viral envelope glycoprotein. There is optimism that a safe and effective human WNV vaccine can be developed.

Prognosis !!navigator!!

In HSV encephalitis treated with acyclovir, 81% survival in one series; neurologic sequelae were mild or absent in 46%, moderate in 12%, and severe in 42%.

Outline

Outline ⬆

Section 14. Neurology