00:02
It's essential to get some spinal fluid
in a patient who has meningitis.
00:10
And when you get some spinal fluid,
during the lumbar puncture,
you will note that the opening pressure is elevated.
00:20
When you microscopically examine the spinal fluid,
you will find that there are too many white cells.
00:28
Now, normally,
there should be no more than five white cells in spinal fluid
and they should be all mononuclear,
lymphocyte or round cells.
00:42
So, it's abnormal if a spinal tap shows even one white cell that’s a neutrophil.
00:49
So, neutrophils are abnormal in spinal fluid.
00:53
There are some exceptions.
00:55
Because of the pace of meningococcal meningitis,
the patient may not have had time to develop
much in the way of white cells.
01:04
This little girl that I told you about
had just one or two neutrophils in her spinal fluid.
01:12
And in infants under four weeks of age,
they may not have white cells in the spinal fluid of that magnitude.
01:23
Now, if they have white cells,
there is a neutrophil predominance,
more than 80% are neutrophils.
01:31
Once again,
the exceptions to that would be a newborn
where they had the cause being something like E. coli
They may not have a neutrophil predominance.
01:43
And also with Listeria.
01:45
Now, if you remember the name of Listeria is Listeria monocytogenes.
01:51
And that implies
that the organism can cause meningitis with mononuclear cells in the spinal fluid.
02:01
So, that's where it got that name.
02:02
Here is a last example: in tuberculous meningitis,
you also find lymphocytosis rather than neutrophil predominance.
02:09
Now, obviously,
when you get some spinal fluid,
you’re going to culture it
and you'll get a positive culture in about 80% of individuals
unless they’ve been given antibiotics.
02:25
And think how many patients go to the physician
and get empirical antibiotics for fever.
02:32
I wonder what's up with that.
02:35
But that may obscure the diagnosis of bacterial meningitis
and the cultures may be negated
or reduced to 60% or 70% positive
if antibiotics had been given.
02:52
It's also important to measure the spinal fluid glucose.
02:58
You'll find that the spinal fluid glucose is lower than it’s supposed to be.
03:03
It'll be usually less than 40 mg/dL in at least 60% of individuals.
03:10
And if you compare the spinal fluid glucose to the serum glucose,
it's less than 31% of the corresponding serum glucose.
03:23
And oftentimes,
it's less than 18 mg/dL.
03:27
It's usually very low.
03:29
And if it's that low,
it's going to be highly predictive of bacterial meningitis.
03:35
The protein is usually elevated,
sometimes quite elevated to 500 mg/dL
And a Gram stain of spinal fluid is essential.
03:48
And you'll find that it's positive.
03:50
It'll predict what you need to treat with
in 60% to 90% of patients.
03:57
You can choose antibiotics on the basis of the Gram stain findings.
04:01
We also can test for bacterial antigens.
04:06
And the best use of it is
when somebody's been given prior antibiotics.
04:11
The bacterial antigens may still be around,
even though the bugs have been partially killed.
04:18
And so, it's used when the Gram stain is negative.
04:22
Unfortunately,
it's not particularly helpful
to do bacterial antigens in urine or serum
in patients with bacterial meningitis.
04:33
Now if we compare these findings to viral meningities,
in the later you would find normal glucose levels, not so high protein levels and lymphocytic predominence.
04:42
Now, I did mention that spinal fluid should be examined
in everybody who's got a suspicion of meningitis,
but there are certain physical findings
that may have -
make you delay doing a lumbar puncture
because if the patient has evidence of increased intracranial pressure,
you may kill them with a lumbar puncture.
05:07
Because if they have markedly elevated intracranial pressure,
if you do a lumbar puncture
and relieve some of that pressure below,
they may actually herniate,
and so the herniation can kill them.
05:23
So, what you need to do is,
if you think there is clinical evidence of an increased intracranial pressure,
you need to verify that with imaging.
05:34
And so,
you have to delay therefore your examination of spinal fluid.
05:40
Where you find Gram-positive diplococci along with a lot of neutrophils?
Is it Haemophilus influenzae,
a very pleomorphic Gram-negative coccobacillus?
Or is it that classic Neisseria meningitidis?
Or is it Listeria monocytogenes,
which are small Gram-positive rods?
And the value of the Gram stain
is that it suggests an etiology before your cultures come back.
06:11
The cultures may not come back for up to 72 hours.
06:15
So, if you've got an idea of what to treat with the Gram stain,
you can design your antibiotic regimen.
06:22
Unfortunately,
the Gram stain is less useful
if the patient has received antibiotics
and it may be negative.
06:32
One thing it doesn't change is the spinal fluid formula.
06:37
The protein still up,
the white count is still up,
the glucose is still low.
06:42
That doesn't usually change with antibiotics.
06:46
Blood cultures are positive in a large number of patients.
06:54
But as you could imagine,
the blood cultures are often negative if antibiotics have been given.
07:00
So, blood cultures are useful
when a spinal tap is contraindicated.
07:08
So, you have evidence that the patient has increased intracranial pressure.
07:12
You’ve got to get cultures from somewhere,
and so getting them from the blood.
07:16
If you get an organism,
you know what to treat.
07:18
There are some rapid tests that we can do on spinal fluid.
07:24
The one that was in vogue when I was training
was the latex agglutination.
07:31
This is no longer used because of the number of false positives.
07:34
We now use immunochromatographic tests,
which are rapid,
they can be done in less than two minutes
and give you an idea of what to treat.
07:47
For example,
in a study showing 450 specimens of cerebral spinal fluid,
122 of them had Streptococcus pneumoniae in them.
08:00
And they were identified by culture in 87 individuals
and 35 were identified by PCR.
08:12
But the bottom line was that
all the patients that had Streptococcus pneumoniae were positive,
so this immunochromatographic test had a sensitivity in this study of 100%.
08:26
It’s probably not quite that good,
but it's pretty good.
08:29
And we can also do PCR,
targeting the 16S ribosomal RNA gene,
which is highly conserved among bacteria.
08:39
So, you can demonstrate that the patient has a bacterial meningitis with PCR.
08:46
It's a little more labor-intensive
and it’s not available immediately.
08:51
But in a study of 206 CSF specimens tested,
17 pathogens were identified by either culture or PCR
and three of them were culture negative,
but PCR positive.
09:07
So, it's showing great promise.
09:08
So, the rapid tests ultimately have a sensitivity of about 100%
and a specificity of more than 95%,
but we still need more studies dealing with these rapid tests.