ACR Codes: 1.2
The herpes virus family, including herpes simplex virus (HSV) is a group of eight double-stranded DNA viruses that can establish latency and lie dormant within living human cells (e.g. neurons). HSV 1 establishes latency in the trigeminal (semilunar) ganglia; while HSV 2 usually resides in the sacral ganglia. [PubMed] HSV 1 may also reside in the geniculate ganglia of the facial nerve, and may cause recurrent Bell's palsy (facial paralysis). Proposed causes of re-activation of latent virus include stress, trauma (including surgery), and relative immune suppression. [PubMed]
The incidence HSE (herpes simplex encephalitis) is estimated at roughly one case per million per year. Herpes labialis (HSV1) is the most common cause of viral encephalitis - representing 90% of herpes simplex encephalitis; and, most of these patients are immunocompetent adults. HSV 2 - herpes genitalis - accounts for most of the remaining 10% of HSE; and, it is most often a neonatal infection, acquired from the mother during vaginal delivery. Immunocompromised patients may also develop HSV 2 encephalitis. [PubMed][PubMed]
» Prognosis: without Tx ~70% mortality, with acyclovir or Valacyclovir, 20-50% mortality
» Diagnosis:
Clinical suspicion!
» Lumbar Puncture: CSF is usually abnormal (95%) [PubMed] CSFglucose is usually normal
Pleocytosis w/Lymphocytes - 10-200/ml
Protein - 60 - 200 mg/dl
PCR is 98% sensitive and > 94% specific [PubMed]
NOTE: CSF PCR is false negative early in disease (24-48 hrs); and, also can be false-negative 10 days to weeks after onset; and, PCR negative or inaccurate with a bloody tap. [PubMed][PubMed]
EEG is abnormal, slowing in temporal and frontal regions
» Imaging with MR is more sensitive than CT. Early gray-matter lesions (bright on FLAIR, T2W, dark on CT T1W, abnormal gyral enhancement) in the temporal, cingulate, subfrontal regions. The cortex may appear thickened. Imaging cannot rule-out HSV encephalitis Depending on the stage and course of the disease, even MR imaging can be "normal" in up to 1/3 of patients with HSE. [PubMed][PubMed]
In patients with abnormal CT and MR imaging, temporal lobe involvement is most common (more than 50%). However, extra-temporal lesions are also seen in about 1/2 of cases; and, up to 1/4 of patients may have only extra-temporal disease. [PubMed][PubMed]
Abnormally decreased ADC values (bright DWI/Dark ADC map) indicate active desctruction of cells; and, may be as senstive as Gd contrast enhancement for HSE. [PubMed]
In more than 1/2 of neonates with HSV2, there may be involvement of the deep gray matter and brainstem [PubMed] The WM and and basal ganglia are less commonly affected in adults with HSV1 -while brainstem lesons are not atypical. [PubMed]
» Treatment: early institution of IV acylovir, TID, 10 mg/kg for 2-3 weeks. Some sources suggest 20 mg/kg in very young children.
NOTE: Any delay in Tx is associated with worse outcome. Acyclovir may be started while PCR is pending. Acyclovir is a specific for HSV infected cells, tolerated well and high safety margin. [PubMed]
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Disease Topic 9786 
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