The subject of this lecture are interstitial lung
diseases. These are non-infective, non-malignant
infiltrations of the lung parenchyma. That
is, they are diseases where the alveoli and
the interstitium, the gap between the alveoli
and the pulmonary capillaries and the rest
of the lung is infiltrated by non-infective and non-malignant
cellular content and extracellular
components. There are a range of diseases
which are in
this category. The most important of which
is lung fibrosis and sarcoidosis. In addition,
there are diseases which are responses to inhaled
substances and antigens such as hypersensitivity
pneumonitis and pneumoconiosis, and a large
range of unusual and very rare interstitial
and infiltrative lung diseases which are normally
included in the ILD category.
In general, ILDs, interstitial lung diseases,
cause a restrictive lung function pattern.
That is they reduce the FEV1 and the FVC.
As you can see on this diagram on the right
hand side here that the ratio between the
FEV1 and FVC is often increased and in fact,
total lung capacity is reduced as well. In
general, CT scans are also essential for an
accurate assessment of these types of diseases.
Pulmonary fibrosis is often a progressive
disease and is actually very difficult
Categorizing ILDs is not straightforward.
This is one way of doing of categorizing ILDs
and is a useful way of thinking about them in
general. So for example, here we have five
categories. On the right hand side, you have
pulmonary fibrosis. That has several different
causes. It could be idiopathic, which is the
commonest cause. It means that we don’t
know what’s causing it. Or it can be associated
with connective tissue disease such as rheumatoid
arthritis or dermatomyositis. In addition,
there are ranges of other situations where
pulmonary fibrosis develops such as radiotherapy,
drug-associated, by various drugs after
adult respiratory distress syndrome.
The other categories are hypersensitivity
pneumonitis, and these are the commonest
causes of that of farmer’s lung and Bird Fancier’s
lungs, and these are immune reactions to inhaled
antigens and is a form of allergy. Sarcoidosis,
the cause of which is unknown is a disease
in which you get infiltration of the lungs
with granulomas and that can present an acute
disease or a chronic disease and it can have
lung involvement, pulmonary sarcoidosis, or
involvement of other organs, extra-pulmonary
sarcoidosis. Then there are pneumoconiosis
which is a non-allergic response to inhaled
substances such as coal dust, asbestosis,
which causes an interstitial lung disease
of various different patterns depending on
what the substance is that you are inhaling.
The last category here are the very rare diseases
which I am not going to discuss in any detail
today, which often cause cold interstitial lung
disease but have their own distinct patterns
and types of infiltrations. Now, very important
components of this diagram are the arrows
showing that patients with severe hypersensitivity
pneumonitis, severe sarcoidosis,severe pneumoconiosis,
and some of the other rare interstitial lung
diseases with aggressive severe diseases, end
up with what looks like pulmonary fibrosis at
the end. So for example, if you have end-stage
sarcoidosis, it actually looks clinically and
radiologically, very similar to end-stage
pulmonary fibrosis. And as a consequence,
sarcoid, hypersensitivity pneumonitis and
various pneumoconiosis are thought of as causes
of pulmonary fibrosis.
Another important point from this slide is that
there are old names to some of these disease.
For example, idiopathic pulmonary fibrosis used
to be called cryptogenic fibrosis alveolitis.
And hypersensitivity pneumonitis used to
be called extrinsic allergic alveolitis.
These terms are interchangeable now.