- Rare- incidence ~0.5/100,000/year
- More common in children and elderly (1/3 are <20 (HSV2) and 1/2 are >50 (HSV1))
- Herpes simplex; Varicella zoster;
- cytomegalovirus; HIV; measles; West Nile; Japanese B
Signs and symptoms
- Usually acute onset headache, fever, focal neurological signs e.g. aphasia, hemiplegia, visual field defects etc and seizures
- Meningism (neck stiffness, photophobia, headache) is not uncommon)
- Other signs e.g. stupor, coma, seizures, partial paralysis, confusion, psychosis, speech/memory problems may also be present.
- NB Herpes simplex infection tends to affect the temporal lobe, so symptoms such as hallucinations, seizures, personality changes and aphasia (particularly receptive) are not uncommon.
- CT may show low-density lesions in the temporal lobes
- Lumbar puncture (once imaging excludes mass lesion) may show RBCs or xanthochromia but more commonly have a mononuclear pleocytosis and raised protein. Glucose is normal and viral PCR may be negative or may indicate causal organism.
- High dose IV Aciclovir (e.g. 10mg/kg TDS for 2-3 weeks)
- Mortality of around 10%; some patients are left with residual epilepsy or cognitive impairment
- NB Herpes simplex encephalitis is notifiable in the UK