Herpes Encephalitis Symptoms
Herpes simplex encephalitis classically presents with fever, altered mental status (confusion, disorientation, behavioral changes), and headache, often accompanied by seizures and focal neurological signs, particularly speech disturbances. 1
Classical Presentation
The most common symptoms at presentation include:
- Fever (91% of adults, 67-80% of children) - though notably, low-grade pyrexia rather than high fever is increasingly recognized 1, 2
- Altered mental status (76% disorientation in adults; 40-76% confusion/behavioral changes in children) 1, 2
- Speech disturbances (59% in adults) - including dysphasia and aphasia 1
- Behavioral/personality changes (41% in adults) 1
- Seizures (33% in adults, 61-78% in children) 1, 2
- Headache with nausea and vomiting 1
- Focal neurological signs (37-78% in children) 2
Increasingly Recognized Subtle Presentations
A critical pitfall is missing atypical presentations. Modern molecular diagnostics (CSF PCR) have revealed that HSV encephalitis can present much more subtly than the "classical" picture 2, 1, 2:
- Low-grade fever instead of high fever
- Isolated speech disturbances
- Behavioral changes mistaken for psychiatric illness or substance intoxication
- Mild encephalitis with minimal symptoms (fever, single seizure, lethargy, headache) 2
The concept of a "classical" picture of HSV encephalitis is now outdated - the most common reason for failure to diagnose is non-specific initial symptoms 2.
Key Examination Findings to Assess
When evaluating suspected cases, specifically look for 2, 1:
- Cognitive function and behavior changes (when assessable)
- Subtle motor seizures (mouth, digit, eyelid twitching)
- Meningism
- Focal neurological deficits
- Evidence of prior seizures (tongue biting, injury)
- Papilledema
Important Clinical Context
In children, presentations differ from adults 2:
- Young children cannot adequately describe headache
- Infants have non-specific symptoms (feeding difficulties, respiratory symptoms)
- 54% had concomitant respiratory signs, 21% gastrointestinal symptoms
- Labial herpes may be present in primary HSV infection (unlike adults where it's non-specific)
Temporal lobe involvement is characteristic, leading to the predominance of memory impairment, speech disturbances, and behavioral changes due to the virus's predilection for temporal and inferior frontal lobes 3.
Critical Diagnostic Caveat
Many conditions mimic HSV encephalitis. In the landmark Whitley study, only 45% of patients undergoing brain biopsy for presumed HSV encephalitis actually had the disease, yet clinical features were very similar between true cases and mimics 2. Common mimics include ADEM, autoimmune encephalitis, and other viral encephalitides. Seizures are more common with cortical involvement (infectious causes) versus subcortical white matter involvement (immune-mediated like ADEM) 2.
The threshold for empiric acyclovir treatment should be low given the devastating consequences of untreated disease, even when the presentation is atypical 2, 1, 2.