How is interstitial lung disease diagnosed?
The typical symptoms and signs of interstitial lung disease, when they occur, should prompt a diagnostic work-up that includes a thorough medical history and physical examination, including blood tests to examine electrolyte levels and blood cells counts.
There is such a wide variety of causes of interstitial lung disease that besides imaging studies, pulmonary function tests, a few blood tests, and often biopsy, other testing should be specific to the findings of a good history and physical.
A history of exposures to environmental toxins may be explored if there is no apparent cause of the symptoms. Often, the precise diagnosis comes from the history if extensive occupational, vocational, travel, and exposure history is obtained.
For example, if a patient has signs and symptoms of a progressive cough and shortness of breath with radiologic findings of diffuse interstitial disease and enjoys raising and caring for pigeons, the likely diagnosis would be hypersensitivity pneumonitis (so called "pigeon breeders lung").
The precise diagnosis of interstitial lung disease may require more specific testing that can include imaging studies or tissue sampling. These rarely give a definitive diagnosis. Diagnostic studies that may be useful are:
- Imaging studies of the chest and lungs are often performed early in the process, when symptoms are apparent. Both chest X-rays and high resolution CT scans of the chest may be ordered. Depending on the history and exam, other testing may be beneficial. For instance, a patient may have arthritic complaints consistent with Rheumatoid arthritis. X-rays of the effected joints may be helpful. Echocardiogram is a test that can evaluate cardiac function as well as the pressures in the lung. This can be useful both for diagnosis and treatment.
- Sometimes blood tests can aid in the diagnosis and or treatment of these patients. Tests for collagen vascular disease (lupus, rheumatoid arthritis), arterial blood gases, liver tests, and others may be beneficial.
- Noninvasive tests that measure lung function are known as pulmonary function tests (PFTs). The most common of these involves forcefully exhaling into a tube, on a device known as a spirometer, to measure lung volume and air flow. These PFTs are usually supplemented with more elaborate testing involving a device known as a body box. This helps measure more accurately the different lung volumes but also can measure gas exchange through the tissue of the lung (diffusing capacity or DLCO).
- Bronchoscopy is the direct visualization and examination of the airways of the lungs using a viewing tube. Biopsies (tissue samples) or washings of the airways are often obtained during this procedure for examination in the laboratory. Usually this does not get an accurate or definitive diagnosis, though it can be helpful to evaluate the possibility of infections, cancer, and sarcoidosis.
- Open lung biopsy is generally necessary if history and less invasive tests are non-diagnostic.
In most major centers, this biopsy is performed by minimally invasive techniques referred to as video assisted thoracic surgery (VATS). This usually only requires a brief hospital stay, sometimes less than 24 hours.