Herpes Simplex Encephalitis (HSV)

Related Subjects: |Herpes Varicella-Zoster (Shingles) Infection |Chickenpox Varicella Infection |Varicella Cerebral Vasculopathy |Herpes Viruses |Herpes Zoster Ophthalmicus (HZO) Shingles |MonkeyPox |Mumps |Measles |Rubella (German Measles) |Epstein-Barr Virus infection |Cytomegalovirus (CMV) infections |CMV retinitis infections |Toxoplasmosis

⚡ Key Clinical Pearl: Always treat suspected HSVE with IV Aciclovir if it’s in the differential. HSVE can mimic a middle cerebral artery (MCA) stroke but clues such as fever 🌡️, seizures ⚡, confusion 🌀, and temporal lobe changes on MRI 🧠 should raise suspicion. It occurs in about 1 per 3,000 stroke cases, meaning a typical UK stroke unit may see one case every 5–10 years.

🧠 About

• HSVE is the most serious form of herpes encephalitis, typically caused by HSV-1 in adults.
• Other viral causes include HSV-2 (more common in neonates) and rarely West Nile virus.

📊 Epidemiology

• Incidence: ~1 case per million per year.
• UK: ~50–100 cases annually, about half in patients >50 years old.
• Presentation can be fulminant with coma, or initially stroke-like ➝ deterioration over hours–days.
• Estimated 12–25 patients per year in the UK present as stroke mimics out of ~100,000 annual strokes.

🦠 Virology & Aetiology

• 90% of adults are seropositive for HSV-1 (latent in trigeminal ganglion).
• Reactivation may occur with stress, trauma, immunosuppression, sunlight ☀️, menstruation, or infection.
• Predilection for the temporal lobes and limbic system ➝ causes haemorrhagic necrosis 💉.
• Spread can be unilateral ➝ bilateral but asymmetric involvement.

🧬 Pathology

• Haemorrhagic necrosis of the inferomedial temporal lobes.
• Limbic system involvement ➝ psychiatric changes, seizures, memory deficits.
• Histology: Cowdry Type A intranuclear inclusions in infected neurons.

🩺 Clinical Features

• Headache + fever + seizures ⚡
• Cold sores on lips or mouth (recent HSV reactivation) 👄
• Confusion, altered behaviour, personality change
• Speech abnormalities, focal deficits (hemiparesis, hyperreflexia)
• Severe cases: coma, raised ICP, death ☠️
• Can appear identical to a stroke with dysphasia and cognitive issues

🔍 Investigations

• FBC: Raised WCC.
• U&E: Hyponatraemia in ~50% (also seen in ~35% of strokes).
• CT/MRI: Temporal lobe oedema, necrosis, haemorrhage; restricted diffusion less intense than stroke.
• CSF: Lymphocytosis, ↑ protein, sometimes blood-stained. HSV PCR = gold standard.
• EEG: Focal temporal slowing, periodic discharges.
• Brain biopsy: Rare, but may show Cowdry A inclusions.

🖼️ Imaging Examples

📖 References

• Herpes simplex encephalitis – JNNP
• HSVE as a stroke mimicker
• Virology Online – HSV

Cases — Herpes Simplex Encephalitis (HSV)

• Case 1 — Acute Confusion and Seizure: A 32-year-old woman presents with fever, headache, and a generalised tonic-clonic seizure. She is drowsy and disoriented. MRI brain: hyperintense lesions in the temporal lobe. CSF: lymphocytic pleocytosis, raised protein, normal glucose. Diagnosis: HSV encephalitis (classic temporal lobe involvement). Management: Immediate IV aciclovir; supportive neuro-ICU care; EEG monitoring if recurrent seizures.
• Case 2 — Psychiatric Presentation: A 24-year-old man develops acute personality change, bizarre behaviour, and hallucinations. No prior psychiatric history. He then develops fever and expressive dysphasia. Diagnosis: HSV encephalitis masquerading as acute psychosis. Management: Urgent IV aciclovir before confirmatory LP/PCR; neuro and psych liaison; seizure precautions.
• Case 3 — Elderly Patient with Delayed Diagnosis: A 70-year-old man is admitted with progressive confusion, fever, and focal seizures over 3 days. Initially treated as delirium. CT head normal, but MRI shows temporal lobe oedema with haemorrhagic change. CSF PCR: HSV-1 DNA positive. Diagnosis: HSV-1 encephalitis (delayed recognition). Management: High-dose IV aciclovir for 14–21 days; monitor renal function; rehabilitation for cognitive and speech deficits.
• Case 4 — Stroke Mimic in an Older Adult: A 68-year-old woman is brought to the ED with sudden-onset confusion, expressive aphasia, and right-sided weakness. Paramedics activated a stroke call. CT head shows no acute infarct. She spikes a fever in hospital and has a focal seizure. MRI reveals left temporal lobe oedema with haemorrhagic changes. CSF PCR is positive for HSV-1. Diagnosis: HSV encephalitis presenting as a stroke mimic (left temporal lobe involvement). Management: Immediate IV aciclovir; supportive care in neuro-ICU; speech and rehabilitation therapy post-acute phase.

Teaching Commentary 🧠

HSV encephalitis is the most common cause of sporadic fatal viral encephalitis, classically due to HSV-1 (HSV-2 more in neonates). Hallmarks: - Fever, headache, confusion, seizures. - Predilection for temporal lobes → dysphasia, hallucinations, behavioural changes. - MRI: temporal lobe hyperintensity ± haemorrhage. - CSF: lymphocytes, ↑protein, normal glucose; PCR confirms HSV. Immediate IV aciclovir should be started empirically (delay worsens prognosis). Complications: seizures, long-term cognitive impairment. Mortality untreated ≈70%, but with treatment ≈20%.