Interstitial lung disease (ILD) is a broad category of lung diseases that includes more than 200 disorders which are characterized by scarring (i.e. “fibrosis”) and/or inflammation of the lungs. ILD accounts for 15 percent of the cases seen by pulmonologists (lung specialists).
Let’s take a look inside the lungs to see what is happening with interstitial lung disease.
In interstitial lung disease, inflammation and/or scarring (fibrosis) occurs in the interstitium of the lung. The interstitium of the lung refers to the microscopic area within the walls of the alveoli (air sacs) between the membrane of the air sac and the membrane of the surrounding blood vessels. Like the leaves on a tree, the alveoli arise from the tiniest bronchioles (airways).
There are hundreds of millions of alveoli in a lung: more than a couple would fit on the period at the end of this sentence. Each alveolus (individual air sac) is surrounded by a network of tiny blood vessels (capillaries) — like mesh encircling the alveolus. The air sac and blood vessels together are called a respiratory unit. This is where the exchange of oxygen and carbon dioxide takes place.
Normally, oxygen passes easily from inside the air sac, through its membrane, across the interstitium and through the membrane of the blood vessel in which red blood cells are lined up and ready to be loaded with oxygen like empty train cars waiting to be filled with cargo. In interstitial lung disease, inflammation, scarring or fibrosis thickens the interstitium, making the lung thick and restricted from filling to their normal capacity and preventing oxygen from passing freely into the bloodstream.
The progression and prognosis of ILD vary from disease to disease and from person to person. It is important to determine the specific form of ILD in each person. What happens over time and what treatments might be useful depend on the diagnosis.
Because there is so much variability in disease behavior, in available therapeutic options and in responses to therapy, and because it is never possible to fully account for a person’s unique characteristics, there is no way to make a blanket statement about prognosis in people with ILD. All people with ILD should be followed closely by a health care provider. This allows for timely assessments of disease status and discussions of prognosis and other aspects of their case.