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Case 5

History:

45 year old male with change in mental status

Findings:

There is FLAIR hyperintensity signal involving the bilateral temporal, parietal lobes and insular cortex.

Diagnosis:

Herpes Encephalitis

Discussion:

Herpes Encephalitis is caused by herpes simplex virus (HSV) type 1. Predilection for temporal, orbitofrontal lobes and limbic system. Patients usually present with change in mental status (97%), fever (90%), and hemiparesis (33%).MRI is the modality of choice show areas of T2 hyperintesity typically involving limbic system (hippocampal, parahippocampal gyrus, orbitofrontal cortex, hypothalamus, Cingulate gyrus, amygdalae and subinsular region) . Can involve cortex and white matter. Micro hemorrhages can be seem on gradient sequences but are usually not the dominant finding. Enhancement usually doesn’t occur until second week. Diffusion can be positive (restricted). HSV CSF antibodies may take up to 14 days to appear, thus is not an optimal study. Brain biopsy: false negative may occur. Usually not necessary in most cases. Must be done within 48 hours of starting acyclovir, or false negative may occur. Anteroinferior temporal lobe is the preferred site for biopsy. If immunohistochemistry is available, diagnosis can be obtained within 3 to 4 hours of biopsy. Biopsy cultures take about 1 week to be positive but must be negative for 3 weeks to be declared negative.

References:

  • Treatment consists on intravenous acyclovir for 2 to 3 weeks. Delirium, dementia, and amnestic and other cognitive disorders. In: Diagnostic and statistical manual of mental disorders: DSM-IV. Washington DC: American Psychiatric Association, 1994.
  • Johnson RT. Acute encephalitis. Clin Infect Dis 1996;23:219-24.
  • Whitley RJ. Herpes simplex virus. In: Scheld WM, Whitley RJ, Durack DT, editors. Infections of the central nervous system, 2nd ed. Philadelphia: Lippincott-Raven, 1997:73-85.
  • Whitley RJ, Lakeman F. Herpes simplex virus infections of the central nervous system: therapeutic and diagnostic considerations. Clin Infect Dis 1995;20:414-20.
  • Wood M, Anderson M. Acute encephalitis. In: Neurological infections. London: W B Saunders 1988:406-17.
  • Gilden DH. Herpes virus infections of the central nervous system. In: Tyler KL, Martin JB, editors. Infectious diseases of the central nervous system. Philadelphia: F A Davis, 1993:76-84.