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Herpes Simplex Encephalitis


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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

About
  • Most serious form is Herpes simplex encephalitis
  • Other causes include West Nile virus
Aetiology
  • HSV-1 has a predilection for the temporal lobes and less so frontal
  • Invades brain parenchyma and may cause haemorrhagic necrosis
Pathology
  • There is haemorrhagic necrosis of the inferiomedial portion of the temporal lobe
  • Disease begins unilaterally, then spreads to the contralateral temporal lobe
Clinical
  • Headache, Fever, Focal seizures and generalised seizures
  • Cold sores on lips or mouth
  • Altered consciousness, and abnormalities of speech and behaviour
  • Hyperreflexia, coma, hemiparesis
Investigations
  • 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
Management
  • 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