Interstitial lung disease

lnterstitial lung disease describes a large group of disorders, most of them causing progressive scarring of lung tissue. The scarring associated with interstitial lung disease eventually affects your ability to breathe and get enough oxygen into your bloodstream. lnterstitial lung disease can be caused by long-term exposure to hazardous materials, such as asbestos. Some types of autoimmune diseases, such as rheumatoid arthritis, also can cause interstitial lung disease. In most cases, however, the causes remain unknown.

Once the  lung scarring occurs, it is generally irreversible. Though medications can slow the damage of interstitial lung disease,  many people never regain full use of their lungs. Lung transplants are an option for some people who have interstitial lung disease.

The histologic abnormalities that characterize interstitial lung disease generally involve the pulmonary interstitium to a greater extent than the alveolar spaces or airways, although exceptions exist. The interstitium is the area between the capillaries and the alveolar space. Usually, this space allows close apposition of gas and capillaries with minimal connective tissue matrix, fibroblasts, and inflammatory cells such as macrophages. It is the interstitium that supports the delicate relation between the alveoli and capillaries, allowing efficient gas exchange. When responding to any injury, whether from a specific exposure, an autoimmune-mediated inflammation from a systemic connective tissue disease (e.g., rheumatoid arthritis), or unknown injury (e.g., idiopathic pulmonary fibrosis), the lung must respond to the damage and repair itself.

All of these pathologic abnormalities may lead to profound impairment in lung physiology. Gas exchange is impaired due to ventilation-perfusion mismatching, shunt, and decreased diffusion across the abnormal interstitium. Work of breathing is markedly increased because of decreased lung compliance. These physiologic impairments lead to the exercise intolerance seen in all of the  interstitial lung disease . Unfortunately, if the initiating injury or abnormal repair from injury is not halted, progressive tissue damage can lead to worsening physiologic impairment and even death.

Most patients with interstitial lung disease have bilateral inspiratory fine crackles, which usually are most prominent at the lung bases. However, some diseases, such as sarcoidosis and lymphangioleiomyomatosis, have only decreased breath sounds without adventitious sounds despite markedly abnormal chest radiographs. Expiratory wheezing is relatively uncommon, and its presence suggests either airway involvement as part of the primary disease process or concomitant airways disease such as emphysema or asthma. Sometimes, wheezing is a clue to a particular diagnosis, such as sarcoidosis, which can involve the airways as well as the interstitium.

Signs of pulmonary arterial hypertension with the right ventricular dysfunction, such as lower-extremity edema or jugular venous distention, may occur late in the course of any interstitial lung disease  and are not helpful in diagnosing a specificinterstitial lung disease.