So how do we evaluate these patients?
Key things are,
especially when you’re worried about bacterial meningitis
is you wanna get your work up done as quickly as possible.
Because we know that the sooner that patient gets antibiotics
the better off they’ll do.
Now often times,
we do start with some basic lab testing,
so a CBC, an electrolytes.
Then you wanna consider checking blood cultures
in a febrile patient,
especially if you’re worried about meningitis.
And those don’t necessarily give you information immediately
but they can help down the line
if the patient is admitted to the hospital
or when they’re admitted to the hospital.
Lumbar puncture is gonna be your test here
that’s gonna give you the answer.
It’s gonna be the test that's gonna tell you
whether or not your patient has meningitis.
So for the most part,
almost every patient in whom there is concern for CSF infection
should get a lumbar puncture.
Now one thing you wanna make sure you do
is you wanna make sure that you
— that you start thinking about whether or not your patient
has elevated intracranial pressure.
Now elevated intracranial pressure
is a contra-indication to doing a lumbar puncture.
So for the most part,
a majority of patients can actually get an LP
if they are able to get a look at the back of their eye
and not see any papilledema
before without getting any neuro imaging.
Now there are a certain subsets of patients
and this is debated in the medical community,
who should most likely get a head CT
before they get a lumbar puncture.
Due to this concern for a mass lesion
or some other process causing their symptoms.
For the most part,
these are patients who are immunocompromised
your concern for a mass lesion or an abscess
or possibly also if a patient presents with seizure,
maybe another indication to get that head CT
before you do the lumbar puncture.
And the main thing that you’re making sure of
is that the elevated intracranial pressure
when you do the lumbar puncture,
the theory that there is,
mostly theoretical risk
that you could cause the patient
to then herniate their brain tissue
due to the fact that you’re caused draining that CSF
from the whole brain spinal fluid column.
So it’s the main thing you wanna make sure you prevent.
Now granted that this is a little bit of a theoretical risk
and there have only been a very rare case reports.
But for the most part,
its gold standard that if you’re worried about that,
that you go ahead and take a look.
Now MRI is a test if you’re worried
about spinal epidural abscessing
and you would get that of the area of the spine
in which the patient would be having pain.
Like I said, lumbar puncture is your test here
that’s gonna give you your answer.
It’s important to note that you do not wanna delay antibiotics.
I’m gonna repeat that.
You do not wanna delay antibiotics.
You wanna give empiric antibiotics prior to the lumbar puncture.
So if someone comes in and they look sick
and you’re worried they have meningitis,
go ahead and treat.
The antibiotics may potentially affect the gram stain
that you send
so they may prevent you from actually looking at the slide
and seeing what bacteria are there.
But they do not affect the cell counts,
they do not affect the culture of the CSF.
Then you wanna make sure that you get your —
that you go ahead and do the lumbar puncture within a few hours
of giving those antibiotics if you’re able to.
But do not delay the antibiotic,
so for the most part,
after you give the antibiotics,
you have between two and four hours
before you need to get that LP
and before that LP is affected.
So go ahead if you’re worried,
give the antibiotics.
Now when you’re doing that lumbar puncture
three to four tubes of cerebral spinal fluid
should be collected if you're able to
The first tube and the fourth tube
are gonna be sent for cell count and differential.
The second tube is sent for protein and glucose levels.
And then that third tube
is sent for any kind of bacterial cultures
or PCRs for the most part.
So any if you’re worried about any viral studies
or anything like that.
So I generally tell people when they’re first doing lumbar punctures,
and first learning how to do it,
to put a little bit more fluid in that third tube.
Just in case you’re not really sure what’s going on,
that’s the tube that they use for the most part to send it out
or to do additional testing for different viral PCRs
and other cultures.
So the lumbar puncture analyze for white blood cells
and red blood cells.
They look for xanthrohcromia
which is if there is concern for blood in the CSF.
The digested blood appears a yellowish color in the CSF.
They look for glucose and protein.
gram stain and culture
and then additional bacterial and viral testing.
Talking for a few moments about the CSF.
So what should be in the CSF?
When it comes to cell count,
pretty much nothing should be there.
So you should have a very low white blood cell count,
less than five.
Very low PMNs so those are the polymorphonuclears cells
and those are the primary cells
that respond to bacterial infection,
less than five eosinophils.
Now in meningitis,
you have increased red blood cell counts
in all types of meningitis and encephalitis.
Primarily PMN count
suggests that it’s a bacterial pathogen, although not always.
So very high white count’s most indicative of meningitis.
you don’t have any organism seen in your cerebral spinal fluid.
It should be a sterile fluid.
And meningitis or encephalitis,
the offending organism maybe in fact seen there,
so it might be seen on the cell that’s made.
Approximately 80% of the time in bacterial meningitis
if again, you patient was pre-treated with antibiotics.
So if they got the antibiotics before the lumbar puncture
that number decrease a bit.
Turbidity, that’s looking at it
and seeing if it looks thick or clear.
Your CSF should be clear.
It should look like water.
So when it’s in the tube,
it should look like something you could drink.
In meningitis, there’s increase turbidity.
So if you do that lumbar puncture
and the fluid comes out yellow
or you know a little cloudy looking,
that should make you even more concerned
that there is an infectious process going on.
none should be there and what that is,
is its caused by red blood cells
being in the spinal fluid for a period of time.
And what that is,
is it's a slight yellowing of the cerebral spinal fluid.
We look at the CSF to serum glucose ratio.
So we’re comparing the level of glucose, the fluid,
to the level of glucose in our blood.
The classic thing here is that in bacterial meningitis,
you have a low glucose level.
I always say that the bacteria go around
and they eat up all the glucose.
If that’s the good way for you to remember,
you can go ahead and use that.
Protein level should be approximately between 15 and 45.
They oftentimes will get elevated in bacterial
or fungal meningitis as well as other conditions
as well in the CSF.
Other things to look for cryptococcal meningitis,
there’s the India ink stain.
This is the classic way this was tested
for where they put India ink on the slide
and they look to see if there is any cryptococcal stuff seen.
The most classic thing that’s done now is the cryptococcal antigen
and the cryptococcal antigen
can actually be measured in the blood as well as in the CSF.
And it has a much higher accuracy for cryptococcal disease
when compared with the India ink stain.
A lactic acid level can be sent
which is elevated in bacterial
and tubercular meningitis.
Bacterial antigen testing can be done
as well as an acid fast stain
which looks for tuberculous meningitis.