Interstitial lung disease (ILD), also known as diffuse parenchymal lung disease, describes a range of disorders that affect the lining of the alveoli (air sacs) in the lungs. Normally, the alveoli expand and contract with ease. Oxygen is absorbed into the bloodstream through the lining of the alveoli (the "interstitium").
In patients with ILD, there is progressive inflammation and/or scarring (fibrosis) of the interstitium. This inflammation and scarring eventually limit the ability of the lungs to expand and adequately absorb oxygen.
Symptoms in patients with ILD tend to develop gradually. Often the only initial symptom is shortness of breath with aerobic activity (such as exercise, walking, or climbing stairs). Over time, however, shortness of breath can occur with even minimal activity or at rest. A dry cough and/or general feelings of fatigue, weakness, and malaise may also occur.
There are many known causes of interstitial lung disease. These can include:
Some patients have a familial predisposition to ILD. However, in many cases, doctors do not know what causes a patient's ILD. In these cases, the disease is called "idiopathic. There are a number of idiopathic ILDs, though the most common one is idiopathic pulmonary fibrosis (IPF).