Signs and Symptoms of HSV Encephalitis
The classic presentation of HSV encephalitis includes fever (present in 91% of adults), altered mental status with disorientation (76%), speech disturbances (59%), and behavioral changes (41%), with one-third experiencing seizures. 1
Core Clinical Features
Most Common Presenting Symptoms
Based on the Association of British Neurologists guidelines, HSV encephalitis typically presents with:
- Fever and febrile illness history - 91% of adults are febrile on admission; even afebrile patients typically report recent fever 1
- Altered mental status - Including disorientation (76%), confusion, lethargy, drowsiness, or progression to coma 1
- Speech disturbances - Dysphasia and aphasia occur in 59% of cases 1
- Behavioral and personality changes - Present in 41% of patients 1
- Severe headache - Often accompanied by nausea and vomiting 1
- Seizures - Occur in approximately one-third of patients, sometimes as the initial presenting feature 1
Focal Neurological Signs
- Focal deficits reflecting temporal lobe involvement
- Meningism (neck rigidity)
- Evidence of prior seizures (tongue biting, injury)
- Subtle motor seizures (mouth, digit, or eyelid twitching) 1
Atypical and Subtle Presentations
A critical pitfall is missing atypical presentations. With modern CSF PCR diagnostics, more subtle presentations are now recognized 1:
- Low-grade pyrexia rather than high fever
- Isolated behavioral changes that can be mistaken for psychiatric illness, drug effects, or alcohol intoxication—occasionally with tragic consequences 1
- Predominant speech disturbances without other obvious neurological signs
- Aggressive behavior and severe cognitive impairment without classic features 2
- Psychotic symptoms including hallucinations and mood disturbances without classic neurological signs 3
Important Clinical Caveat
The Glasgow Coma Score is a crude tool for detecting subtle behavioral changes in HSV encephalitis. Some patients present with normal GCS despite significant encephalitis 1. Look specifically for alterations in higher mental function, personality changes, and subtle cognitive deficits rather than relying solely on GCS.
Key Distinguishing Features
Factors Suggesting HSV Encephalitis Over Other Causes
- Lateralization signs (odds ratio 4.7) 4
- Altered level of consciousness (odds ratio 0.27) 4
- Temporal lobe involvement on neuroimaging (nearly pathognomonic when bilateral) 5
- Cortical involvement (seizures more common with cortical processes) 1
Features Suggesting Alternative Diagnoses
Consider non-encephalitic processes if:
- Past history of similar episodes
- Symmetrical neurological findings
- Myoclonus or asterixis
- Lack of fever
- Acidosis or unexplained negative base excess 1
Pediatric Considerations
In children, the presentation differs 6:
- Fever (67-80%)
- Seizures (61-78%)
- Confusion, irritability, or behavioral changes (76%)
- Focal neurological signs (37-78%)
- Decreased consciousness (47%)
- Vomiting (57%)
- Young children cannot adequately describe headache
- Infants present with non-specific symptoms including feeding and respiratory difficulties
- 54% have concomitant respiratory symptoms; 21% have gastrointestinal symptoms 6
Critical Timing Factors
Delays in recognition are associated with worse outcomes. 7, 8 Chronic alcohol abuse is one factor associated with delayed treatment initiation 1. The duration of disease before hospital admission and extent of brain involvement on MRI are independent risk factors for poor prognosis 7.
The key to reducing morbidity and mortality is maintaining a high index of suspicion for HSV encephalitis in any patient presenting with fever plus altered consciousness, new seizures, or new focal neurological signs, even when the presentation is atypical. 1