Hey, everybody, this is Rishi and this is going to be
the second video in my series on interstitial lung disease.
Today we're going to be talking about UIP.
This is the roadmap that we're going to be using for today.
First, I'm going to be talking about the radiologic pattern of UIP.
Then I'm going to talk briefly about IPF, then we're going to talk about
the differential diagnosis, and then how to differentiate UIP-IPF
from UIP due to connective tissue disease.
All right.
So let's start with the radiologic diagnosis of UIP.
So this is a consensus statement that was put out by
the American Thoracic Society, the European Respiratory Society,
the Japanese Respiratory Society and the Latin American Thoracic Society.
And this was a clinical practice guideline about the diagnosis of IPF.
One of the useful tools that this article contained
was this table that contained guidelines on how to diagnose
UIP from a chest CT.
And the diagnosis was divided into these four categories UIP,
Probable UIP, indeterminate for UIP
and alternative diagnosis.
I'd like to first focus on this
UIP category, this first column here.
So the classic patient with UIP on CT
will have a basilar and subpleural distribution of fibrosis
with honeycombing, reticulation
and traction bronchiectasis.
Now, if you'll notice this is the second column of probable UIP.
This is exactly the same as the first column,
except that instead of having honeycombing,
these patients with a probable UIP pattern don't have honeycombing.
So if you see a patient who has a basilar
and sub plural distribution of fibrosis with reticulation
and traction bronchiectasis, then that's a probable UIP pattern.
Whereas if you see that same patient but they have honeycombing,
that is a UIP pattern.
And what's important about these two categories
is that if you have a high confidence that the patient has either UIP
or probable UIP, then that patient
will not require a biopsy for further evaluation.
There's been many studies that have shown that a radiologic
diagnosis of UIP with a high degree of confidence
correlates very highly with UIP on pathology.
So the only patients who might require
a biopsy in these two categories
are those patients whose clinical history
doesn't jive with having a UIP pattern.
Now, if you look at the distribution,
sometimes the apical-basilar gradient isn't super well-defined.
So if you have honeycombing, reticulation and traction bronchiectasis,
but it's still subplural, and yet there's no significant apical-basilar gradient,
that's still enough to put it in this UIP, or probable UIP category.
And sometimes the disease is asymmetric,
so up to a quarter of patients will have extensive disease on one side--like
their left lung will have extensive fibrosis
and their right lung will only have mild to moderate fibrosis.
That's OK.
Those patients can still be put in these two categories.
Now, let's look for a second, we'll skip indeterminate for a second,
and let's look at the alternative diagnosis category.
So there's two ways that you can have an alternative diagnosis.
One is you can have the wrong distribution.
And by wrong distribution, Imean that the distribution is upper to mid lung
or the fibrosis is in the central part of the lung,
rather than in the sub pleural or peripheral part of the lung.
OK, that's where this peribronchovascular and perilymphatic comes in.
So one, you can have the wrong distribution
or two, if you see other findings that suggest another diagnosis,
for example, cysts might make you think of some cystic lung disease,
mosaic attenuation, particularly when you see it on the expiratory
images might make you think of chronic hypersensitivity pneumonitis.
Ground glass opacity, consolidation, nodules.
All of these things might make you think of another diagnosis.
Or if you see things in other parts of the chest
outside of the lungs like pleural plaques, a dilated esophagus,
clavicular erosions, lymphadenopathy, all of these
things might make you think of another diagnosis rather than UIP.
Now this indeterminate for UIP category
I think of in two different ways, and they're right here.
One is the early UIP pattern.
So these are patients whose degree of fibrosis is
just not enough to put a name on it.
These are patients who have very minimal fibrosis
or reticulation or traction bronchiectasis.
It's just not quite enough to meet the threshold of these other two.
And then the second thing in this category
are patients who have a distribution of disease
that you can't put over here in the UIP or probable UIP.
And yet it also doesn't meet the criteria of an alternative diagnosis.
And these patients, I put in this indeterminate for UIP category.
Finally, before moving on, you can have ground glass opacity
in a patient with UIP or probable UIP.
But it's important that that ground glass opacity isn't extensive.
It shouldn't be more than the amount of fibrosis,
and it really should be limited to the areas
that have traction, bronchiectasis and reticulation.
In other words, if you see isolated areas of ground glass
opacity by themselves without accompanying fibrosis,
then that goes in this alternative diagnosis category.
But if you see it in areas where there is fibrosis and it's mild,
you can put it in the UIP or probable UIP category.
Let's take a look at some examples.
So in this first case, I have an axial and sagittal image,
and you can see that it's subplural or peripheral predominant.
And on the sagittals, you can see that it's basilar predominant.
And when we zoom in on the fibrosis, you can see that
there are these cystic airspaces in the periphery of the lung.
This is honeycombing with reticulation.
So we have a patient with subpleural and basilar fibrosis with honeycombing.
Therefore, the diagnosis here is UIP.
And importantly,
we didn't see any of those things that make it an alternative diagnosis.
Like we didn't see a bunch of ground glass opacity, nodules,
consolidation, cysts, et cetera.
In this second case, we have axial and sagittal images again.
And on the axial images, you can see that the fibrosis is central or peribronchial
in distribution, and the craniocaudal distribution is mid-lung predominant.
And in fact, when we look at the bases, the bases are spared here.
So that would
mean that this patient has an alternative diagnosis.
This patient was diagnosed with chronic hypersensitivity pneumonitis.
I didn't show you the expiratory images here, but this patient had moderate
to extensive expiratory air trapping.
Now, take a look at this case,
in this case, we have peripheral or subpleural fibrosis,
and it's basilar predominant,
but the degree of fibrosis is very mild.
There's no honeycombing here.
There's a bit of ground glass and reticulation,
but there is just not enough disease here.
And I would call this one indeterminate for UIP.
This case, on the other hand, has a little bit more disease.
So there's peripheral and subpleural
fibrosis with reticulation,
and you can see on the sagittal images that it's basilar predominant.
There is a little bit of ground glass opacity, but the ground glass
opacity is confined to the areas that have the reticulation.
So this patient, I would likely call probable UIP.
Now a colleague of mine might call this indeterminate for UIP, and that's OK, too.
They might think that this amount of fibrosis doesn't quite
meet the threshold for calling it probable UIP.
And if I'm on the fence about it, I might take a look
at some of the additional clinical history, like the patient's age
or their smoking history to kind of tip the scales one way or the other.
So speaking of that,
let's look at idiopathic pulmonary fibrosis.
So the typical patient with IPF will present
with gradual dyspnea on exertion and cough.
Patients are usually older and the incidence increases with age,
especially if you reach age about 60 or so,
then that curve starts to go up quite a bit.
It's a little bit more common in males than females,
although not so much so that you don't see it in females.
It's not rare in females by any means.
Most patients are smokers.
I've seen prevalence rates between 40% and 80%.
And then finally, IPF is idiopathic, so these patients shouldn't have any
connective tissue disease, exposures, drug reactions, et cetera.
Now, when we talk about
the differential diagnosis, there's two ways to think about this.
If the patient has a typical UIP pattern on the CT,
then we're really only talking
about the clinical differential diagnosis.
And as I mentioned in part one of this series,
most of the patients with a UIP pattern will have IPF.
But a good minority of patients will have other things like connective
tissue disease, hypersensitivity, pneumonitis,
asbestosis and even sarcoid.
Now, if we don't have a typical UIP pattern on CT
and we have either a probable
or indeterminate pattern on CT,
then the differential moves into a radiologic differential
and the radiologic differential includes things like fibrotic NSIP
and chronic hypersensitivity pneumonitis.
Now, I mentioned that a minority of patients with UIP will have a specific
etiology, like a connective tissue disease rather than IPF.
This article by Jonathan Chung and others looked at a few different
radiologic signs to help differentiate patients
with UIP due to IPF
from UIP due to connective tissue disease.
By the way,
Jonathan Chung has a YouTube channel about thoracic radiology
that includes a lot of great cases that he goes over in detail.
So I'm going to link to that below, and I encourage you to check it out.
Let's take a look at this article, though.
So the three pulmonary signs that were identified
are the exuberant honeycombing sign, the anterior
upper lobes sign, and the straight edge sign.
So if you see any of these signs on CT, it's more likely that you're
looking at a patient with UIP secondary to connective tissue disease
rather than idiopathic pulmonary fibrosis.
Let's look at these signs a little bit more in detail.
The exuberant honeycombing sign is when you see that most of the fibrosis
is honeycombing rather than reticulation or traction bronchiectasis.
And usually when I see this sign,
the amount of fibrosis is quite extensive as well.
Like in this example, the honeycombing is taking up
most or all of the lower lobes.
OK, so this is the exuberant honeycombing sign.
The anterior upper lobe
sign is when you have focal fibrosis in the anterior upper lobes
with a relative sparing of the other portions of the upper lobes.
And it's often helpful to look at the sagittals for the anterior
upper lobe sign where you'll see basilar and peripheral fibrosis
in the lower lobes, as well as anterior subpleural fibrosis
in the upper lobes.
And then finally, the straight edge sign.
So the straight edge sign is something that you see on the coronal images.
So you have to go to the coronal images
and then scroll posteriorly to where you see the spine.
And what you'll see is that the basilar fibrosis has
this sharp demarcation in the craniocaudal dimension.
So this is a positive straight edge sign.
In a patient with IPF, what you'll see is a less well demarcated
edge of fibrosis, and the fibrosis tends to creep up
the lateral edge of the lung rather than stop abruptly.
All right.
So if you see any of these three signs: exuberant honeycombing,
anterior upper lobe, or straight edge sign,
any or all of these signs are good indicators that you have connective
tissue disease associated UIP
rather than IPF associated UIP.
OK, to wrap up,
we talked about the radiologic pattern of UIP.
We talked about the different categories: UIP, probable
UIP, indeterminate, and alternative diagnosis.
We talked about the demographics
of idiopathic pulmonary fibrosis.
We talked about both the clinical differential
for UIP and the radiologic differential.
And then we talked about some ways that you can differentiate UIP-IPF
from UIP associated with connective tissue disease.
If you have any questions about anything we talked about today.
Please leave them in the comments below. Thanks.