What are the symptoms of Herpes Simplex Virus (HSV) encephalitis?

Symptoms of Herpes Simplex Virus (HSV) Encephalitis

HSV encephalitis presents with fever, altered mental status, headache, and seizures as the most common symptoms, though presentations can vary from subtle behavioral changes to severe neurological deficits requiring prompt recognition and treatment to reduce mortality and morbidity. 1

Core Clinical Features

Common Presenting Symptoms

• Fever (present in 80-91% of cases)
• Altered mental status/consciousness (40-76% of cases)
  • Confusion
  • Disorientation (76% of adult cases)
  • Behavioral changes (41-76% of cases)
  • Personality changes
  • Lethargy and drowsiness
• Headache (often severe)
• Seizures (33-61% of cases)
• Speech disturbances (59% of cases)
  • Dysphasia
  • Aphasia
• Focal neurological deficits (36-78% of cases)
• Nausea and vomiting 1, 2

Less Common or Associated Symptoms

• Meningism (neck stiffness)
• Low-grade pyrexia (rather than high fever in some cases)
• Subtle motor seizures (mouth, digit, or eyelid twitching)
• Memory impairment (becomes more prominent in long-term sequelae)
• Anosmia (loss of smell)
• Movement disorders 1, 3

Age-Specific Considerations

Adults

• More likely to present with classic symptoms of fever, headache, and altered mental status
• Speech disturbances (59%) and disorientation (76%) are particularly common
• One-third experience seizures during the acute phase 1, 2

Children

• May have more non-specific symptoms
• Often unable to adequately describe symptoms like headache
• May present with feeding difficulties and respiratory symptoms
• Concomitant respiratory infection signs (54%) and gastrointestinal symptoms (21%) are common
• Behavioral changes, irritability, and confusion (76%) are frequently observed 1

Atypical Presentations

HSV encephalitis can present atypically, which may lead to delayed diagnosis:

• Seizures as the sole initial manifestation (without other encephalitic features) 4
• Low-grade fever instead of high fever
• Psychiatric-like symptoms that can be mistaken for primary psychiatric illness
• Subtle behavioral changes without obvious neurological deficits
• Mild encephalitis with minimal symptoms (lethargy, headache) and normal imaging 1

Diagnostic Pitfalls

1. Non-specific initial symptoms are the most common reason for failure to diagnose HSV encephalitis
2. Normal Glasgow Coma Score at presentation doesn't exclude HSV encephalitis
3. Absence of fever at presentation doesn't rule out HSV encephalitis (though history of fever is typical)
4. Behavioral changes may be mistaken for psychiatric illness, drug or alcohol effects
5. Labial herpes (cold sores) may be present in children with primary HSV infection but has no diagnostic specificity in adults 1

Risk Factors for Poor Outcomes

• Delayed hospital admission (longer duration of disease before treatment)
• Extensive brain involvement on MRI at admission
• Acute symptomatic seizures (associated with 8-fold increased risk of developing post-encephalitis epilepsy) 5, 2

Long-term Sequelae

Despite treatment with acyclovir, many patients develop long-term complications:

• Memory impairment (69%)
• Personality and behavioral abnormalities (45%)
• Epilepsy (24%)
• Anosmia (65%)
• Dysphasia (41%) 3

Early recognition of HSV encephalitis symptoms and prompt initiation of acyclovir treatment (within 5 days of symptom onset) is crucial for improving outcomes and reducing mortality, which has decreased significantly with appropriate antiviral therapy 6, 2.