What starts with ‘E’, ends in ‘S’,  and makes you lose your mind?

Not encephalitis.

Exams. Coming soon 😥

Well, encephalitis too.


Definition: inflammation of the brain parenchyma

Aetiology/risk factors:

-Cause is usually viral and often never identified

-May have history of travel or animal bite

Viral: HSV-1 & 2 (most common in UK), CMV (immunocompromised), EBV, VZV, HIV, measles, mumps, rabies (Asia), tick-borne encephalitis, adenovirus, coxsackie, echovirus, enteroviruses, arboviruses transmitted by mosquitoes e.g. Japanese B encephalitis, St. Louis Encephalitis and West Nile Virus (USA)

Non-viral: any bacterial meningitis, syphilis, S.aureus, TB, malaria, listeria(immunocompromised), Lyme disease, legionella, leptospirosis, aspergillosis, Cryptococcus, schistosomiasis, typhus, toxoplasmosis (immunocompromised).

-Autoimmune or paraneoplastic

Epidemiology: annual UK incidence = 7.4 in 100,000

Symptoms: in many cases encephalitis is a mild self-limiting disease with a sub-acute onset (hours to days)

Infectious prodrome:


-acute, severe headache, felt over most of head


-neck stiffness, photophobia (meningism)



Infectious prodrome:

-rash, lymphadenopathy, cold sores, conjunctivitis

-Meningism: neck stiffness, Kernig’s sign (pain and resistance on passive knee extension with hip fully flexed)

After infectious prodrome:

-odd behaviour, confusion

-drowsiness/decreased consciousness (↓GCS)

-focal neurological signs e.g. hemiplegia, dysphasia


Signs of raised intracranial pressure: hypertension, bradycardia, papilloedema (on fundoscopy)


Consider encephalopathy if there is no infectious prodrome (e.g. hypoglycaemia, hepatic encephalopathy, DKA, drugs, hypoxic brain damage, uraemia, SLE, beri-beri)


Bloods: FBC (↑lymphocytes), U&Es (SIADH may occur), blood cultures, ABG, viral serology-serum for viral PCR, toxoplasma IgM titre, malaria film

Throat swab, MSU (mid-stream urine)

-Urgent CT head (MRI if allergic to contrast)

-Exclude mass lesion

-Focal bilateral temporal lobe involvement (oedema on MRI) suggests HSV encephalitis


Image result for hsv encephalitis mri

MRI- Herpes Simplex Encephalitis


-Meningeal enhancement suggests meningoencephalitis

-Lumbar puncture- if no raised intracranial pressure (risk of brain herniation with LP). Look for signs of infection in the cerebrospinal fluid (CSF). Send CSF for viral PCR, including HSV.

= Moderately elevated CSF protein and lymphocytes, and decreased glucose

Electroencephalogram (EEG)- urgent EEG showing diffuse abnormalities may help confirm encephalitis but does not indicate cause. May show epileptiform activity e.g. spiking activity in temporal lobes.


-Often wise to treat before exact cause known

ACICLOVIR within 30 minutes (10mg/kg/8h IV over 1h), adjusting dose to eGFR (estimated glomerular filtration rate)

-Specific therapies for CMV and toxoplasmosis

-Toxoplasmosis: Pyrimethamine + sulfadiazine

-CMV: Ganciclovir IV or oral valganciclovir, foscarnet, cidofovir

-Supportive therapy, in HDU or ICU, if needed

-Mechanical ventilation if respiratory failure, monitor vital signs closely

-Manage fluid balance, resuscitate if needed, risk of cerebral oedema (consider dexamethasone)

-Symptomatic treatment e.g. PHENYTOIN for seizures, antipyretics, antiemetics, analgesia for headache


-post-encephalitic neurological sequalae, particularly epilepsy and cognitive impairment in 10-30% with variation according to viral aetiology.


-Mortality in untreated encephalitis is approx. 70%.

-Treated mortality is 20%.

-Survivors may have epilepsy or cognitive impairment. (More risk if > 30 years old, GCS < 6 on initiation of treatment).

References: Cheese & Onion, Rapid Medicine




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