Now, when somebody comes in
with altered mental status
and signs of encephalitis,
we certainly are going to examine
the cerebrospinal fluid if it's safe.
And so, what we’re going to look for is the cytology.
And what you would expect,
unlike bacterial meningitis,
is a lymphocytic pleocytosis.
There may be some neutrophils there, but
there is a predominance of mononuclear cells.
Unlike bacterial meningitis,
your glucose is normally not low.
The protein may be elevated.
Those are the classic findings, but the
exceptions to the rule are the West Nile virus,
which may have more neutrophils in it
and Eastern equine encephalitis
may have a neutrophil predominance.
And the cell count is going to be 50 to 500 cells.
To make a specific diagnosis, we have
to rely on PCR and antibody studies.
The herpes simplex PCR is very sensitive
and very specific and we use it all the time.
For varicella zoster,
it's not nearly so sensitive,
but it does have a high specificity.
Culturing these viruses is not particularly useful.
So, serology is important
and we’re going to get an
acute serum on admission
and then periodically get convalescence serum,
looking for antibody rises.
We can do PCR on gastrointestinal samples,
respiratory secretions and skin vesicles
and they're pretty sensitive and specific.
But if we just can't figure out
why the patient has encephalitis
and the patient is deteriorating,
then we may need to resort to a brain biopsy.
These are usually done through a
burr hole and a needle aspirate.
Neuroimaging is important in
patients who have encephalitis
and the MRI is the study of choice.
And particularly, in herpes simplex virus,
90% of the time you're going to
be looking in the temporal lobes.
Varicella zoster produces multifocal hemorrhage and infarction
and a West Nile virus has less frequent
abnormalities than herpes simplex virus.
We don't do EEG very often,
but if you were to do it,
you'd find generalized slowing
in most forms of encephalitis.
And in herpes, you’d find,
once again, abnormalities
like spikes in the temporal lobe.
And you’d find that in a majority of
patients with herpes virus encephalitis.
And this, for example,
is what herpes virus encephalitis looks like.
Notice the predominance in both
temporal lobes in this patient.
Notice the multifocal location in the
patient with varicella zoster encephalitis.
And notice that in West Nile virus,
the encephalitis is highlighted by
increased signal in the basal ganglia.
And remember, we talked about parkinsonism,
and so that fits with West Nile virus.
The enteroviral encephalitis,
you can have increased
signal in both hemispheres.