MEDICAL DISCLAIMER:The contents are under continuing development and improvements and despite all efforts may contain errors of omission or fact. This is not to be used for the assessment, diagnosis or management of patients. It should not be regarded as medical advice by healthcare workers or laypeople. It is for educational purposes only. Please adhere to your local protocols. Use the BNF for drug information. If you are unwell please seek urgent healthcare advice. If you do not accept this then please do not use the website.

Herpes Simplex Encephalitis

Learning objectives

  • Learning
  • Understand
  • Integrate
  • Reflect

Treat with IV Aciclovir if this is in the differential. Can cause a focal neurological deficit and appear identical to a temporal infarct in a patient who is otherwise well. Clues - pyrexia, cold sore, MRI changes, seizure, progression

  • Most serious form is Herpes simplex encephalitis
  • Other causes include West Nile virus
  • HSV-1 has a predilection for the temporal lobes and less so frontal
  • Invades brain parenchyma and may cause haemorrhagic necrosis
  • There is haemorrhagic necrosis of the inferiomedial portion of the temporal lobe
  • Disease begins unilaterally, then spreads to the contralateral temporal lobe
  • Headache, Fever, Focal seizures and generalised seizures
  • Cold sores on lips or mouth
  • Altered consciousness, and abnormalities of speech and behaviour
  • Hyperreflexia, coma, hemiparesis
  • CT/MRI to exclude abscess will show lesions in the temporal lobes. May be necrosis and haemorrhage
  • CSF - raised lymphocytes and elevated protein. Bloody CSF can result in a falsely negative PCR as the porphyrins can interfere with the assay
  • HSV: also check enteroviral PCR or WNV (West Nile virus) if suspected.
  • MRI - asymmetrical temporal lobe changes with HSV with inflammation, swelling and even necrosis
  • EEG - slowing and periodic discharges
  • Brain Biopsy - HSV encephalitis may show neuronal inclusion bodies called Cowdry Type A found in the nucleus
Poor prognostic indicators
  • Age > 30, Coma at presentation, Bilateral EEG abnormalities
  • High CNS viral load, Treatment delayed (4 days), abnormal CT
  • If you have any suspicion of the diagnosis at all then treat with IV Aciclovir even if it turns out to be wrong. Untreated HSV is a tragedy.
  • Treatment threshold must be very low initially. Studies show that Mortality was significantly reduced in Aciclovir-treated patients (28 percent versus 54 percent)
  • IV Aciclovir 10 mg/kg TDS is given for 2-3 weeks.
  • Monitor renal function, hydration and NG feeding as required.
  • Often initially managed in HDU setting. Of those who survive there is a high risk of ongoing neurological deficits.
  • There is no evidence base for steroids. Treat any seizures.
  • For the most severe cases hemicraniectomy may be need for decompression
Late complications
  • Long term sequelae are seen in half of those treated such as poor memory, emotional lability, poor concentration, irritability, depression