00:01
Let's look first at Mycobacterium
tuberculosis as the most recognizable cause
of disease. Humans are the only lucky
natural reservoir for
disease for this organism.
00:13
Typically, the organism is transmitted
through respiratory droplets and not your
typical small droplets, such as you would
get with sneezing but large, heavy
droplets. In fact, the contagious area
related to a respiratory droplet from
somebody with tuberculosis is within three
to at most six feet,
unless they have cavitary disease, which
we'll examine shortly, in which case their
droplets are large and are coughed or
expressed with high velocity.
00:43
Who then is at risk for tuberculosis?
Unfortunately, anybody, especially if they
live in an endemic area.
00:50
However, there are classic risks and those
are the elderly or the young,
i.e. those with immature or waning immunity
and patients who are
immunocompromised. For whatever reason.
01:02
The x ray that you see on this slide shows a
Cavitary tuberculosis lesion.
01:07
A patient with a lesion such as that
outlined by the arrows would be highly
contagious if they're coughing.
01:14
And again, those with cavitary lung disease,
regardless of the age, are highly
contagious but still within a somewhat
limited spatial distance.
01:24
So let's look a bit more closely at the
pathogenesis of Mycobacterium
tuberculosis. Or as I might abbreviate in
this lecture MTB.
01:34
First is the inhalation aspect.
01:36
You might be a happy, innocent casual
bystander standing next to somebody with
cavitary TB.
01:43
They might cough, you might inhale.
01:45
And in go the acid fast bacilli the MTB.
01:50
Next, as you are lowering the organism into
your airways the
bacteria. The MTB will be phagocytosed
typically by
alveolar macrophages.
02:01
They are part of the innate immunity present
in your respiratory tissue, which are very
good at at eating or phagocytosing for
material such as
in this case, our MTB bacteria as that
alveolar
macrophage ingests or phagocytosis the MTB,
it has on
its own a triggering of pro-inflammatory
cytokines such as you see listed on the
slide, especially the Interleukins one, 12
and
18, which will stimulate by cytokine
pathways a local
inflammatory reaction.
02:38
Next will be induction of interferon gamma
VI triggered
T lymphocytes, especially those that are CD8
positive and CD4
positive. And you can see that mechanism on
the slide as well.
02:51
One gets an interaction between the alveolar
macrophage, which has been stimulated
by ingestion of the MTB, and then further
release of
pro-inflammatory cytokines, including the
interferon gamma, which are supposed to
induce bacterial killing.
03:07
In addition to that, TNF alpha tumor
necrosis factor alpha is another
pro-inflammatory cytokine which is
precipitated in its release by the
presence of MTB within the alveolar
macrophage.
03:21
All of these steps occur sort of in a
sequential but also simultaneous
fashion, creating to the growth of a
granuloma or a localized
site of infection with the MTB, and the
entire process is meant to
control growth of the MTB, to limit it from
infecting additional cells
and proliferating in a typical fashion that
also means
to control the further growth or further
proliferation of MTB,
that continuous cytokine stimulation and
continuous immune surveillance must occur.
03:57
That means that granuloma, which is forming,
is an entire cluster of
activated, actively secreting immune cells,
all which are tasked
to limit this further spread of MTB.
04:10
That is fantastic.
04:11
That's great. The macrophages contribute to
that and they continue to be part of the
activated process.
04:17
The problem occurs when the process breaks
down.
04:20
And this is what's referred to as post
primary tuberculosis.
04:24
The first step that we just described is the
initial infection.
04:28
Most often there are no symptoms associated
with it unless the patient is
immunocompromised. Most often then the
patient has what is called
latent tuberculosis infection TB.
04:41
That's the first stage in which the organism
is ingested into the lungs, walled off
within the granuloma, and sits there,
hopefully in a quiet fashion forever.
04:51
However, sometimes things break down and
when they do, it's due
to a failure in that ongoing
immunosurveillance such as we see here.
05:01
When that happens, the MTB is able to
proliferate, evade its
macrophage ingestre, and cause further
proliferative disease, and that
then allows for disease to reactivate
disease is the presence of
actual symptom signs and clinical
symptomatology associated with the
infective presence of an organism within the
cell.
05:25
When that happens, then damage of nearby
bronchi occur, damage of alveoli occur,
and one gets to the spread of MTB to other
areas of the lung.
05:34
This is post primary tuberculosis.
05:38
What can happen further is in patients who
have a specific
immunodeficiency. And here we turn our minds
to those patients with HIV Aids
in which their CD4 T lymphocyte cell
function is either compromised or
absent. When that occurs, there is no hold,
no no
limit to associate with, and the and the
granulomas develop
even further into pulmonary disease.
06:06
If the CD4 function is absent and the
macrophages are unable to
proliferate and release pro-inflammatory
cytokines in response, then
granulomas don't even occur and one has free
ranging or completely
overwhelming MTB infection in the lung.
06:23
This is the state in patients with HIV Aids.
06:28
So let's look a little bit more closely then
at what happens in the stages in
tuberculosis infection.
06:34
And we start again with primary TB.
06:37
The initial infection occurs with the first
aspiration of the MTB into the
airways. And then hopefully it's walled off
into the granuloma.
06:47
However, within several years of infection,
if immunosurveillance
decreases, up to 10% of patients may develop
active disease.
06:57
When that occurs, the disease occurs in the
mid and lower lobes.
07:00
There's higher oxygen tension there.
07:03
And so those organisms can grow a little bit
more expediently.
07:07
What may develop then in the specific and
focal setting of an infection
would be something called the gone focus, in
which the MTB is proliferated
in the subpleural area, causing necrosis or
a gone complex,
which also involves the higher lymph nodes.
07:25
The entire process creates a focal infection
which has not yet spread
throughout the lung. Patients at this stage
of infection may have a very
nonspecific presentation.
07:36
They may appear simply flu like, so malaise,
low
grade fevers, they may have some night
sweats, they may have a cough.
07:45
They may have weight loss.
07:46
At some point, the cough may progress to
become productive of bloody sputum
or hemoptysis in patients with active
tuberculosis, meaning that the
disease is now evaded its immune mediated
controls and is
progressing. Those patients will develop
further cough, further malaise, further night
sweats. Everything is amplified to a power
of ten or so.
08:10
And these are patients that, on plain
radiography on the x rays, will show evidence
of pneumonitis and hiler lymphadenopathy,
progressing then into
secondary tuberculosis.
08:21
This is the reinfection step.
08:23
So after the initial aspiration and with now
lack of
immune suppression patients will develop
progressive disease going
from that focal area.
08:34
Perhaps that go and focus into cavitary
lesions throughout the lung
fields themselves. And here, with increasing
oxygen tension in the upper
lobes, the disease will progress into
cavitary lesions.
08:47
Miliary spread is a reference to millet
seeds, which are the way that
these illnesses look on x ray.
08:55
Tiny little dots of focus of disease spread
throughout the lung fields.
09:01
This also can be associated with recurrence
of new clinical manifestations
and further hemoptysis.
09:08
Now, a patient may go between primary TB
infection and the secondary TB infection
for months, years or even decades, or
potentially until they become older and have
a waning of their immunity.
09:20
Those patients who are overtly
immunocompromised, whether they are
immunosuppressed due to medications or have
acquired HIV infection,
progressing to Aids, or have undergone
treatment of cancer with
chemotherapy, any compromising of the immune
system can allow for
extrapulmonary disease to occur.
09:41
Now this also has in parentheses miliary TB.
09:44
Because tuberculosis preferentially occupies
and creates infection
in only a few small foci throughout the
lungs.
09:53
However, when that immune control
evaporates, those small foci can then
disseminate throughout the lung fields,
causing that miliary or millet seed
appearance, but the bacteria can also spread
throughout the blood and the
lymph system to go throughout the entire
body.
10:10
And as you can see listed on the slide, many
patients will develop disease throughout
the genital urinary system, central nervous
system, the kidneys, and in fact,
the kidneys are the most common
extrapulmonary site.
10:23
The symptoms and signs of clinical disease
in this case are nonspecific,
except that patients may have ongoing weight
loss, they may develop skin
lesions, and they may develop clinical
evidence of multiple organ dysfunction.
10:38
Diagnosis. As mentioned before, the mycolic
acid present in the cell
wall of MTB is acid fast, and so one can
perform
an acid fast stain on induced sputum or on a
biopsy specimen
and look for the organisms such as you see
here on the slide.
10:58
Isolation also can occur through culturing
the organism on lowenstein-jensen culture
media, but it requires 3 to 6 weeks for MTB
to grow.
11:07
It's quite a slow grower, which again goes
along with the onset of
disease. It's a slow process.
11:15
We, however, can look for immune recognition
of infection with MTB
by placing a tuberculin skin test, which is
known as PPD or purified
protein derivative. If the patient has been
exposed to or
infected with MTB and developed an
immunologic reaction,
they will then mount a type four
hypersensitivity reaction or a delayed type
hypersensitivity, also known as, and create
an erythematous or
a red raised nodular reaction to placement
of the
PPD in the intradermal intradermal excuse me
space.
11:54
Now, importantly, one has to read the amount
of the induration to
accurately describe the result of a PPD.
12:02
Unfortunately, a common clinical mistake is
to simply measure the diameter of
the redness surrounding the reaction.
12:10
That, however, is not the true indurated
reaction by Deloitte.
12:14
Excuse me, delayed type hypersensitivity.
12:17
Instead, one should measure the thick
indurated raised component,
and one can do that by taking a simple
ballpoint pen, and on the arm of the site
is drawing a line until you reach the edge
of that indurated raised spot.
12:31
Do so in all four directions, and then
measure the diameter between the ends of the
pen line. That's the true induration, not
the full amount of the redness or the
erythema. Now, there are several reasons
that some may have a false
positive or a false negative.
12:48
Ppd a common reason to have an exaggerated
PPD reaction
is if the patient had previously had a PPD
placed certainly within the last
48 to 72 hours, or even in the last 2 to 4
weeks,
because one would have precipitated a
reaction by delayed type
hypersensitivity to replace and rechallenge.
13:10
The immune system that way would create an
even more exaggerated response, because
those innate immune cells are already and
still activated.
13:19
In fact, in hospital infection control
practices, we call the whole process
a two step PPD, placing an initial PPD,
measuring
the result, then placing a second PPD two
weeks after the first,
measuring the result.
13:35
Again, it's a good way to bring out a very
slow or early reaction to somebody who
might just have been exposed to tuberculosis
infection.
13:45
A common cause of false negative results
will be medications and recent
infections, especially recent infections
that in part suppress the immune
system. Infections with some of the herpes
viruses, such as Epstein-Barr virus
infection or cytomegalovirus, can absolutely
suppress the immune reaction.
14:04
An infection like HIV, which specifically
targets CD4 cells, can absolutely
cause a false negative, as can granulomatous
diseases such as sarcoidosis.
14:15
And again, those who are very old or very
young.
14:18
Use of steroids has an unpredictable
interaction
with the development of a delayed type
hypersensitivity, and so a false negative
could occur in a patient who recently has
received either systemic or oral
steroids. A classic reason for a positive
PPD is
receipt of the BCG vaccine, which is given
in many parts of the world, and
it's difficult to interpret.
14:43
Then a PPD in a patient who received such a
vaccine.
14:47
Is it a true positive meaning they actually
do have MTB, or is it simply
a low reaction which is precipitated by
having received the BCG vaccine in the
past treatment?
Assuming that one has now confirmed presence
of MTB infection, the treatment is
ripe. No, not what you probably smell like
after studying for a very long
time, but ripe. The four initials of the
four anti-tuberculosis drugs that
typically are used rifampin, isoniazid,
pyrazinamide
and ethambutol.
15:20
Easy to remember if you can just remember
ripe.
15:23
All four drugs are started together for the
first part of treatment for a
tuberculosis infection, and those are used
for the first two months of treatment.
15:33
Then just the rifampin and isoniazid are
used together for.
15:38
For another four months total of six months
treatment, but only the first two months of
which have all four drugs.
15:44
The right treatment prevention well
prevention in part
depends on recognition, and thus all health
care workers undergo
annual screening by PPD looking for prior
infection with or
exposure to the MTB organism.
16:01
Prevention. Well prevention in part depends
on recognition,
and thus all health care workers undergo
annual screening by PPD looking
for a prior infection with or exposure to
the MTB organism.
16:16
Additionally, the US Preventive Services
Task Force recommends screening all
patients at risk of TB infection.
16:24
This may include individuals who were born
or lived in regions with a high prevalence,
or individuals who have lived in certain
congregate settings, such as homeless
shelters or correctional facilities.
16:35
Those who are positive will likely undergo
some treatment to help
minimize the reaction likelihood and
development of secondary tuberculosis.
16:45
Similarly, the BCG vaccine can be
administered to those who are very young
and living in an endemic part of the world.
16:53
And then for those who are exposed, some
cases deserve prophylactic isoniazid
or in if they are in high risk.