Differentials
Herpes simplex encephalitis
SIGNS / SYMPTOMS
Temporal lobe symptoms (e.g., memory loss, olfactory hallucinations, behavioural abnormalities).
INVESTIGATIONS
Polymerase chain reaction (PCR) of cerebrospinal fluid (CSF): positive for herpes simplex virus.
Brain CT or MRI: presence of temporal lesions.
EEG: presence of unilateral temporal lobe encephalitis.
Herpes zoster encephalitis
SIGNS / SYMPTOMS
Usually presents as a stroke or transient ischaemic attack.
INVESTIGATIONS
PCR of CSF: positive for varicella-zoster virus.
Serology of CSF: positive for antibodies to varicella-zoster virus.
Magnetic resonance angiography: presence of vasculitis or aneurysm of cerebral arteries.
West Nile virus
SIGNS / SYMPTOMS
Residence in/travel from West Nile virus-endemic region.
Signs or symptoms may mimic B virus infection.
May present with flaccid paralysis, especially in older adults.
INVESTIGATIONS
Serology of CSF: positive for antibodies to West Nile virus.
Epstein-Barr virus (EBV) encephalitis
SIGNS / SYMPTOMS
Cerebellar signs predominate (e.g., personality changes).
INVESTIGATIONS
Serology: positive for EBV-specific antibodies to EBV.
PCR: positive for EBV.
Viral meningitis
SIGNS / SYMPTOMS
No definite differentiating signs or symptoms.
INVESTIGATIONS
PCR of CSF: positive.
Brain CT or MRI: absence of brainstem encephalitis.
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