Encephalitis (HSV and Autoimmune)

Encephalitis is inflammation of the brain parenchyma presenting with fever, altered consciousness, behavioural change, seizures, and focal neurology. HSV encephalitis is the commonest viral cause — aciclovir 10mg/kg IV TDS must be started…

NICE NG162 / ENCEPH Trial / BNF

The pathway

1 · Recognise and treat immediately — start aciclovir now

Do NOT wait for LP or MRI before starting aciclovir
Clinical diagnosis: fever + altered consciousness/behaviour + headache = encephalitis until proven otherwise
Aciclovir 10mg/kg IV over 1 hour TDS within the first hour
Simultaneously: blood cultures, LP if safe, CT head, MRI brain
Immediate neurology or infectious disease referral

2 · ABCDE and initial stabilisation

Airway: GCS ≤8 → anaesthetics for intubation immediately
Seizures: lorazepam 4mg IV → see status epilepticus pathway
SpO₂ ≥94%, high-flow O₂
Glucose: exclude hypoglycaemia as seizure/confusion cause — BM immediately
Temperature: manage fever with paracetamol

3 · Lumbar puncture — if safe

Contraindications: papilloedema, focal neurology, immunosuppression, coagulopathy, recent seizure → CT head first
CSF analysis: send for HSV PCR (and VZV, enterovirus, EBV, CMV if indicated)
Typical HSV CSF: lymphocytic pleocytosis (50–200 cells), elevated protein (0.5–1.5 g/L), normal glucose
Also send CSF autoimmune encephalitis panel (anti-NMDAR, anti-LGI1, anti-CASPR2, anti-GABA-B)
Red cells in CSF common in HSV (haemorrhagic encephalitis)
Normal CSF does NOT exclude HSV — continue aciclovir until PCR result

4 · MRI brain

MRI with gadolinium is the imaging of choice
HSV encephalitis: temporal lobe signal change on FLAIR/DWI (unilateral or bilateral), haemorrhage, insular involvement
Autoimmune encephalitis (anti-NMDAR): MRI often normal (or subtle limbic changes)
CT head: normal in early encephalitis but excludes other lesions and contraindications to LP
Urgent EEG: may show PLEDs (periodic lateralised epileptiform discharges) in HSV; delta brush in anti-NMDAR

5 · Autoimmune encephalitis — suspect if atypical features

Anti-NMDAR: young woman, psychiatric prodrome (paranoia, hallucinations), orofacial dyskinesias, autonomic instability, hypoventilation
Anti-LGI1: older male, faciobrachial dystonic seizures (FBDS) — brief arm + face jerks before encephalopathy
Anti-CASPR2: hyperekplexia, peripheral nerve involvement, Morvan syndrome
Treatment: methylprednisolone 1g IV daily for 3–5 days + IVIG 2g/kg over 5 days
Plasmapheresis if no response
Tumour screen mandatory: CT chest/abdomen/pelvis, pelvic USS, testicular USS — teratoma most common in anti-NMDAR

6 · Duration of treatment and safety netting

Continue aciclovir for 14–21 days (21 days if immunocompromised)
Even if HSV PCR negative on early LP: repeat LP at 48–72 hours if clinical suspicion remains — early PCR can be falsely negative
Do NOT stop aciclovir on the basis of a single negative LP if clinical picture fits
Switch to oral valaciclovir after IV course if good response: 1g TDS for 90 days (reduces relapse risk)
Neuropsychological follow-up: memory, behaviour, and executive function commonly affected post-HSV

Drugs

Drug	Dose	Route	Notes
Aciclovir	10mg/kg IV over 1 hour every 8 hours	IV	Start immediately — do not wait for LP/MRI. Duration 14–21 days. Adjust in renal impairment (eGFR-based). Hydrate well to prevent crystalluria.
Lorazepam	4mg IV	IV	Acute seizure management. See status epilepticus pathway if ongoing. Levetiracetam for maintenance.
Levetiracetam	500mg BD PO/IV	PO or IV	Maintenance anticonvulsant. Titrate to 1000–3000mg/day. Fewer interactions than phenytoin.
Methylprednisolone	1g IV daily for 3–5 days	IV	Autoimmune encephalitis first-line. Give with omeprazole cover. Monitor blood glucose.
IVIG	2g/kg IV over 5 days	IV	Autoimmune encephalitis alongside steroids. Human immunoglobulin — check IgA levels first (risk of anaphylaxis in IgA deficiency).
Dexamethasone	0.15mg/kg IV every 6 hours	IV	If bacterial meningitis cannot be excluded: give dexamethasone before or with first antibiotics. Not routinely given in confirmed viral/autoimmune encephalitis.

When to escalate

GCS ≤8 — immediate anaesthetics for airway; ITU admission,Status epilepticus — full ALS benzodiazepine ladder, ITU, phenobarbital or propofol if refractory,Clinical suspicion of HSV but negative early LP — repeat LP at 48–72h, do NOT stop aciclovir,Autoimmune encephalitis not responding to steroids + IVIG — plasmapheresis (5 exchanges over 10 days), rituximab for refractory anti-NMDAR,Raised ICP (papilloedema, Cushing's triad) — mannitol 0.5–1g/kg IV, neurosurgery, avoid LP,Anti-NMDAR with found ovarian teratoma — urgent oncology + gynaecology; teratoma removal can trigger remission

Reference: NICE NG162 Encephalitis 2022 / Lancet Neurology ENCEPH Guidelines / BNF Aciclovir Dosing

This page is the reference half

The app adds what a web page cannot: a VINDICATE differential builder, worked on-call scenarios with full A–E findings, recall practice, and all of it offline.