HSV Encephalitis
Reviewed and revised 2 February 2014
OVERVIEW
- severe viral infection of the central nervous system, caused by a herpes simplex virus and usually localised to the temporal and frontal lobe
- most commonly identified cause of infectious encephalitis
- 5-10% of encephalitis cases worldwide
- affects all ages, but is most common, and most severe, in children (33% <20y) and the elderly (50% >50y)
- the classic triad of fever, headache and altered
CAUSE
- HSV-1 encephalitis is more common in adults
- HSV-2 infection is more common in neonates
CLINICAL FEATURES
Classic presentation
- flu-like illness with malaise, N&V (50%), headache (80%) and fever (90%)
- followed by seizures (may be focal; 70%), cognitive impairment (25%), behavioural changes (70%), and/ or focal neurological deficits (33%)
Variable presentation patterns are common, such as
- absent viral prodrome
- altered mental state may only be subtle
- focal neurological deficits (may resemble stroke or other neurological disorders)
Prodromal symptoms and focal deficits are less common in the immunocompromised
INVESTIGATIONS
Approach
- MRI (or CTB if MRI not available)
- LP (unless contra-indicated; e.g. mass effect on imaging or coagulopathy)
- other tests guided by condition and need to exclude other diagnoses
MRI is the diagnostic modality of choice
- abnormal in 90%; but changes are not specific for HSV (e.g. limbic encephalitis, MCA ischaemia, tumours, effects of seizures)
- hyperintense T2 signal in the medial temporal lobes, inferior frontal lobes and insula
- Basal ganglia are usually spared
- T1 signal is hypointense, consistent with edema
- Mild patchy gyral or cisternal contrast enhancement may occur
- Diffusion weighted imaging and FLAIR may be more sensitive for early HSV encephalitis than T2 weighted images
Lumbar puncture/ CSF
- raised lymphocyte count (10–500×106/L, average 100×106/L)
- +/- RBCs +/- xanthochromia (encephalitis may be haemorrhagic)
- mildly raised protein levels
- normal or mildly decreased glucose
- HSV PCR
— sensitivity 96–98%, specificity 95–99%
— may be undetectable early; consider repeat after 3-7 days
— remains positive for 5-7 days after antiviral therapy
— brain biopsy now no longer needed
Electroencephalography
- high sensitivity (84%) but low specificity (32%) for diagnosis of HSV encephalitis
- may detect non-convulsive seizures
MANAGEMENT
Specific treatment
- acyclovir 10mg/kg IV q8h (adults) for 14-21 days
Supportive care and monitoring
- treat seizures
- ICP monitoring and control if indicated
- appropriate supportive care for a patient with decreased level of consciousness (e.g. airway management, pressure cares)
If bacterial meningitis is possible then also start empiric antibiotics until the diagnosis is confirmed
PROGNOSIS
- untreated: >70% mortality
- treated: <20% mortality; 25% have epilepsy or neuropsychiatric sequelae
OTHER INFORMATION
Diagnosis is commonly delayed
- variable clinical presentations
- neuropsychiatric presentations, such as amnesia
- reluctance to perform invasive lumbar punctures in atypical presentations when utility is less certain
- non-diagnostic investigations
— CSF is normal in 5–10% of patients, particularly in children
— CTB is normal in the 1st week in 1/3 patients
— MRI brain is normal in 10%
— PCR may be negative initially
References and Links
CCC Neurocritical Care Series
Emergencies: Brain Herniation, Eclampsia, Elevated ICP, Status Epilepticus, Status Epilepticus in Paeds
DDx: Acute Non-Traumatic Weakness, Bulbar Dysfunction, Coma, Coma-like Syndromes, Delayed Awakening, Hearing Loss in ICU, ICU acquired Weakness, Post-Op Confusion, Pseudocoma, Pupillary Abnormalities
Neurology: Anti-NMDA Encephalitis, Basilar Artery Occlusion, Central Diabetes Insipidus, Cerebral Oedema, Cerebral Venous Sinus Thrombosis, Cervical (Carotid / Vertebral) Artery Dissections, Delirium, GBS vs CIP, GBS vs MG vs MND, Guillain-Barre Syndrome, Horner’s Syndrome, Hypoxic Brain Injury, Intracerebral Haemorrhage (ICH), Myasthenia Gravis, Non-convulsive Status Epilepticus, Post-Hypoxic Myoclonus, PRES, Stroke Thrombolysis, Transverse Myelitis, Watershed Infarcts, Wernicke’s Encephalopathy
Neurosurgery: Cerebral Salt Wasting, Decompressive Craniectomy, Decompressive Craniectomy for Malignant MCA Syndrome, Intracerebral Haemorrhage (ICH)
— SCI: Anatomy and Syndromes, Acute Traumatic Spinal Cord Injury, C-Spine Assessment, C-Spine Fractures, Spinal Cord Infarction, Syndomes,
— SAH: Acute management, Coiling vs Clipping, Complications, Grading Systems, Literature Summaries, ICU Management, Monitoring, Overview, Prognostication, Vasospasm
— TBI: Assessment, Base of skull fracture, Brain Impact Apnoea, Cerebral Perfusion Pressure (CPP), DI in TBI, Elevated ICP, Limitations of CT, Lund Concept, Management, Moderate Head Injury, Monitoring, Overview, Paediatric TBI, Polyuria incl. CSW, Prognosis, Seizures, Temperature
ID in NeuroCrit. Care: Aseptic Meningitis, Bacterial Meningitis, Botulism, Cryptococcosis, Encephalitis, HSV Encephalitis, Meningococcaemia, Spinal Epidural Abscess
Equipment/Investigations: BIS Monitoring, Codman ICP Monitor, Continuous EEG, CSF Analysis, CT Head, CT Head Interpretation, EEG, Extradural ICP Monitors, External Ventricular Drain (EVD), Evoked Potentials, Jugular Bulb Oxygen Saturation, MRI Head, MRI and the Critically Ill, Train of Four (TOF), Transcranial Doppler
Pharmacology: Desmopressin, Hypertonic Saline, Levetiracetam (Keppra), Mannitol, Midazolam, Sedation in ICU, Thiopentone
MISC: Brainstem Rules of 4, Cognitive Impairment in Critically Ill, Eye Movements in Coma, Examination of the Unconscious Patient, Glasgow Coma Scale (GCS), Hiccoughs, Myopathy vs Neuropathy, Neurology Literature Summaries, NSx Literature Summaries, Occulocephalic and occulovestibular reflexes, Prognosis after Cardiac Arrest, SIADH vs Cerebral Salt Wasting, Sleep in ICU
Journal articles
- Big C, Reineck LA, Aronoff DM. Viral infections of the central nervous system: a case-based review. Clin Med Res. 2009 Dec;7(4):142-6.PMC2801692.
- Sabah M, Mulcahy J, Zeman A. Herpes simplex encephalitis. BMJ. 2012 Jun 6;344:e3166. PMID: 22674925.
FOAM and web resources
- Radiopaedia.org — HSV encephalitis
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.
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