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Acute Encephalitis ✅

🧠 Acute encephalitis is a neurological emergency. Treatment should be started promptly on the basis of the likely diagnosis, rather than waiting for all results. HSV encephalitis can mimic acute stroke, particularly with focal deficits such as aphasia, hemiparesis, seizures or temporal-lobe signs. Perform urgent lumbar puncture if safe, and arrange early MRI brain where available. Start IV aciclovir immediately if HSV encephalitis is reasonably suspected, and continue until HSV is excluded or an alternative diagnosis is confirmed. Aciclovir is effective but not benign: it can cause acute kidney injury, especially with dehydration or renal impairment, so check renal function, adjust dose and ensure good hydration. Always take urgent senior, neurology and/or infectious diseases advice.

🧠🚨 Initial Encephalitis Management Summary
🫁 Stabilise ABCDE → admit urgently, monitor observations, treat seizures, consider HDU/ITU if reduced GCS, airway risk, recurrent seizures, shock or severe autonomic instability. 💉 Immediate investigations: bloods including FBC, U&E/creatinine, LFT, CRP, glucose, clotting, blood cultures and venous/arterial gas if unwell. Check renal function before/while giving aciclovir, but do not delay aciclovir if HSV is suspected. 🧪 CSF: perform urgent lumbar puncture if safe. Send CSF for cell count, protein, glucose with paired plasma glucose, Gram stain/culture and viral PCR including HSV and VZV; consider enterovirus and other tests depending on context. 🖼️ CT before LP only if indicated: do not routinely delay LP for CT. Image first if there are features suggesting raised intracranial pressure or mass lesion, such as papilloedema, new focal neurology, significantly reduced or deteriorating GCS, recent seizure with persistent reduced consciousness, immunosuppression, anticoagulation/bleeding risk, or concern about space-occupying lesion. 💊 IV aciclovir: give 10 mg/kg IV every 8 hours immediately if HSV encephalitis is suspected. Adjust dose in renal impairment, ensure good hydration and monitor creatinine/eGFR. 🧪 Empirical antibiotics: if bacterial meningitis cannot be excluded, give empirical IV ceftriaxone or cefotaxime according to local/NICE meningitis pathway. Add amoxicillin if Listeria risk, such as older age, pregnancy, immunosuppression or relevant comorbidity. 🧲 MRI brain: arrange early MRI where available; it is more sensitive than CT for encephalitis and may show temporal/frontal signal change in HSV. ⚡ EEG: request if ongoing seizures, reduced consciousness, suspected non-convulsive status epilepticus, or diagnostic uncertainty. 📞 Urgent specialist input: discuss with neurology, infectious diseases/microbiology and ICU/anaesthetics where severe.

🧠🚨 Initial Encephalitis Management Summary

🫁 Stabilise ABCDE → admit urgently, monitor observations, treat seizures, consider HDU/ITU if reduced GCS, airway risk, recurrent seizures, shock or severe autonomic instability.
💉 Immediate investigations: bloods including FBC, U&E/creatinine, LFT, CRP, glucose, clotting, blood cultures and venous/arterial gas if unwell. Check renal function before/while giving aciclovir, but do not delay aciclovir if HSV is suspected.
🧪 CSF: perform urgent lumbar puncture if safe. Send CSF for cell count, protein, glucose with paired plasma glucose, Gram stain/culture and viral PCR including HSV and VZV; consider enterovirus and other tests depending on context.
🖼️ CT before LP only if indicated: do not routinely delay LP for CT. Image first if there are features suggesting raised intracranial pressure or mass lesion, such as papilloedema, new focal neurology, significantly reduced or deteriorating GCS, recent seizure with persistent reduced consciousness, immunosuppression, anticoagulation/bleeding risk, or concern about space-occupying lesion.
💊 IV aciclovir: give 10 mg/kg IV every 8 hours immediately if HSV encephalitis is suspected. Adjust dose in renal impairment, ensure good hydration and monitor creatinine/eGFR.
🧪 Empirical antibiotics: if bacterial meningitis cannot be excluded, give empirical IV ceftriaxone or cefotaxime according to local/NICE meningitis pathway. Add amoxicillin if Listeria risk, such as older age, pregnancy, immunosuppression or relevant comorbidity.
🧲 MRI brain: arrange early MRI where available; it is more sensitive than CT for encephalitis and may show temporal/frontal signal change in HSV.
⚡ EEG: request if ongoing seizures, reduced consciousness, suspected non-convulsive status epilepticus, or diagnostic uncertainty.
📞 Urgent specialist input: discuss with neurology, infectious diseases/microbiology and ICU/anaesthetics where severe.

📖 About

Encephalitis means inflammation of the brain parenchyma. It is usually viral, but can also be autoimmune, bacterial, fungal, post-infectious or paraneoplastic.
HSV encephalitis is the key treatable diagnosis not to miss. Early aciclovir improves survival and neurological outcome.
Presentation may overlap with meningitis, sepsis, stroke, intoxication, metabolic encephalopathy and psychiatric illness.
Prognosis depends on the cause, immune status, age, level of consciousness at presentation, seizure burden and speed of treatment.

🦠 Causes & Features

Cause	Clinical Features	Investigations	Treatment
Viral HSV, VZV, enterovirus	Fever, headache, confusion, altered behaviour, seizures, aphasia, hemiparesis or other focal neurology.	CSF lymphocytic pleocytosis, raised protein, viral PCR. MRI may show temporal/frontal hyperintensity in HSV. EEG may show temporal abnormalities or diffuse slowing.	IV aciclovir if HSV/VZV suspected, supportive care, seizure control, treat complications.
Autoimmune e.g. anti-NMDA receptor encephalitis	Psychiatric features, memory loss, seizures, dyskinesias, movement disorder, autonomic instability, reduced consciousness.	Serum and CSF neuronal antibodies, CSF oligoclonal bands, MRI often normal or non-specific, EEG diffuse slowing. Consider tumour screening where relevant.	Steroids, IVIG, plasma exchange ± rituximab/cyclophosphamide under specialist care; treat underlying tumour if found. Do not delay aciclovir while HSV remains possible.
Bacterial / atypical Listeria, TB, Mycoplasma and others	Fever, headache, confusion, meningism, seizures, cranial nerve signs or focal deficits.	CSF may show neutrophils or lymphocytes depending on pathogen, raised protein, low glucose in bacterial/TB causes, Gram stain/culture/PCR as appropriate. MRI may show abscess, rhombencephalitis or meningeal enhancement.	Empirical IV antibiotics if meningitis cannot be excluded; add amoxicillin for Listeria risk. Tailor treatment to microbiology.
Fungal Cryptococcus, Aspergillus and others	Often subacute headache, fever, confusion, meningism, cranial nerve palsies; more common in immunocompromised patients.	CSF fungal culture/antigen, cryptococcal antigen, imaging for nodules, infarcts, abscesses or raised ICP.	Specialist antifungal therapy, for example amphotericin-based regimens for cryptococcal disease, plus management of raised ICP where relevant.

🧠 Clinical Presentation - especially HSV

Core features: fever, headache, altered mental state, confusion or behavioural change.
Seizures: focal or generalised seizures are common and may progress to status epilepticus.
Focal neurology: aphasia, hemiparesis, visual symptoms, cranial nerve signs or temporal-lobe features may occur.
Psychiatric presentation: agitation, psychosis, personality change or hallucinations can occur, particularly in autoimmune encephalitis but also in HSV.
Do not be reassured by absent meningism: encephalitis may occur without neck stiffness.

🔬 Investigations

Bloods: FBC, U&E/creatinine, LFT, CRP, glucose, clotting, blood cultures, HIV test where appropriate, and autoimmune/infective tests guided by clinical context.
Renal function: check creatinine/eGFR before and during aciclovir treatment; dose-adjust if renal impairment develops.
CSF: cell count, protein, glucose with paired plasma glucose, Gram stain/culture, HSV/VZV PCR and other viral PCRs as indicated.
CSF HSV PCR: highly useful, but if performed very early and clinical suspicion remains high, seek specialist advice about repeat LP/PCR rather than stopping aciclovir prematurely.
MRI brain: preferred imaging test where available; HSV classically affects temporal and frontal lobes, but imaging can be normal early.
CT head: useful before LP when contraindications exist, or to assess alternative diagnoses such as haemorrhage, tumour, abscess or large infarct.
EEG: useful for seizures, non-convulsive status epilepticus, diffuse encephalopathy and supportive diagnostic evidence.

💊 Management

IV aciclovir: 10 mg/kg every 8 hours for suspected HSV encephalitis. Treat for at least 14 days if confirmed, often 14–21 days depending on severity, immune status and specialist advice.
Renal safety: ensure good hydration, avoid nephrotoxins where possible, monitor U&E/creatinine and adjust dose in renal impairment.
Antibiotics: if meningitis cannot be excluded, give empirical IV ceftriaxone or cefotaxime according to local/NICE pathway. Add amoxicillin for Listeria risk.
Seizures: treat promptly with benzodiazepines for acute seizures and antiseizure medication such as levetiracetam, phenytoin or alternatives according to local status epilepticus guidance.
Supportive care: IV fluids, antipyretics, nutrition, pressure-area care, VTE prevention when safe, aspiration precautions, delirium care and rehabilitation planning.
ITU/HDU: consider for reduced GCS, airway compromise, recurrent seizures/status epilepticus, shock, severe autonomic instability, raised ICP or need for ventilation.
Raised ICP / cerebral oedema: urgent neurocritical care, neurology/neurosurgery and ICU input. Use head-up positioning and avoid hypoxia/hypercapnia. Hyperosmolar therapy such as mannitol or hypertonic saline should be specialist-led. Hyperventilation is a short-term emergency bridge only, not routine treatment.
Autoimmune encephalitis: consider early when psychiatric symptoms, movement disorder, autonomic instability or refractory seizures are prominent. Send serum/CSF antibodies and involve neurology; immunotherapy should be specialist-led after infection has been considered and treated.

⚠️ Poor Prognostic Features

Older age.
Coma or markedly reduced GCS at presentation.
Delay to aciclovir in HSV encephalitis.
High seizure burden or status epilepticus.
Focal neurological deficits.
Abnormal neuroimaging, especially extensive or bilateral disease.
Immunosuppression.
High viral load or persistent positive HSV PCR despite treatment, where assessed by specialists.

⏳ Late Complications

Memory impairment and cognitive decline, especially after temporal-lobe involvement.
Epilepsy or recurrent seizures.
Mood, personality and behavioural changes, including irritability, anxiety or depression.
Fatigue, sleep disturbance and reduced executive function.
Need for neurorehabilitation, neuropsychology, occupational therapy and community support.

💡 Teaching pearl: Encephalitis is not simply “infection plus confusion”. It is inflammation of brain tissue, so seizures, aphasia, behavioural change and focal neurology are part of the syndrome. HSV has a predilection for temporal and frontal lobes, which is why it can look like stroke, psychosis or epilepsy. Early aciclovir is brain-saving, but it should be prescribed thoughtfully with renal dosing and hydration.

📚 References

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