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Practice Easily Missed?

Herpes simplex encephalitis

BMJ 2012; 344 doi: (Published 06 June 2012) Cite this as: BMJ 2012;344:e3166
  1. Mazen Sabah, neurology specialist registrar1,
  2. James Mulcahy, consultant physician2,
  3. Adam Zeman, professor of cognitive and behavioural neurology3
  1. 1Neurology Department, Southampton General Hospital, Southampton SO16 6YD, UK
  2. 2Acute Medicine Department, The Royal Devon and Exeter Hospital, Exeter, UK
  3. 3Peninsula Medical School, University of Exeter, Exeter
  1. Correspondence to: M Sabah m3sab3{at}

How common is herpes simplex encephalitis?

  • Herpes simplex was the most commonly identified cause of infectious encephalitis in a large prospective UK study1

  • It accounts for 5–10% of all cases of encephalitis worldwide2

  • The annual incidence of herpes simplex encephalitis is 0.2–0.4/100 000 in the general population3

  • It affects either sex, with no seasonal variation1

  • It affects all age groups but is most common and severe in children and elderly people.4 About 33% of patients are aged less than 20 years, and 50% are over 50 years at presentation

  • Of the two types of herpes simplex virus (HSV-1 and HSV-2), HSV-1 encephalitis is more common in adults, and HSV-2 infection is more common in neonates2

  • Other herpes viruses that cause encephalitis include varicella zoster virus, Epstein-Barr virus, cytomegalovirus, and human herpes viruses 6 and 7

The wife of a previously healthy 40 year old man requested a domiciliary visit from their general practitioner for her husband, who had been in bed for a few days with “bad flu,” fever, and headache. She was worried that he was becoming quite confused and unable to recall recent events. The GP finds the patient is febrile, agitated, and disoriented in time and place. Concerned about encephalitis, he sends the patient immediately to hospital. There a CT scan shows an area of decreased attenuation in the right temporal lobe and a lumbar puncture a raised lymphocyte count, both suggesting herpes simplex encephalitis. Aciclovir treatment is immediately started.

What is herpes simplex encephalitis?

Herpes simplex encephalitis is a severe viral infection of the central nervous system that is usually localised to the temporal and frontal lobes in adults. Typically, it causes a flu-like illness with headache and fever …

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