Interstitial lung disease (ILD) is not a single ailment but a group of over 200 disorders characterized by inflammation and progressive scarring, known as fibrosis, in the lung tissue. This scarring affects the interstitium, the network of tissue that supports the lungs’ tiny air sacs (alveoli). As this tissue thickens and stiffens, it becomes more difficult for oxygen to pass into the bloodstream, leading to symptoms like shortness of breath. Because many distinct conditions fall under the ILD umbrella, arriving at a precise diagnosis is a methodical process. Identifying the exact type of ILD is the primary goal, as this determination directly influences treatment.
The Initial Evaluation
The diagnostic process begins with an initial evaluation. A physician will conduct a comprehensive medical history to build a picture of a person’s health and potential exposures. Questions cover the specifics of symptoms, family history of lung or autoimmune diseases, and a full review of all medications. A part of this history is a discussion about occupational and environmental exposures, including contact with substances like asbestos, silica dust, mold, or bird proteins.
Following the medical history, a physical examination is performed to identify signs of lung disease. A physician uses a stethoscope to listen to the lungs, as many forms of ILD cause a characteristic crackling sound during inhalation. These sounds are often described as being similar to the noise of Velcro being pulled apart and can indicate that further investigation is warranted. This combination of patient history and a physical exam guides the next steps.
Imaging and Function Tests
After the initial consultation, non-invasive tests are used to visualize the lungs and measure their performance. A chest X-ray is often one of the first imaging tests ordered. It provides a broad view of the chest, helping to identify abnormalities or rule out other conditions like pneumonia or heart failure. While useful for screening, a standard X-ray may not show the subtle changes of early-stage ILD.
For a more detailed look, a high-resolution computed tomography (HRCT) scan is the primary imaging test for diagnosing ILD. An HRCT uses specific techniques to capture thin, cross-sectional images of the lungs with exceptional clarity. This allows a radiologist to see precise patterns of inflammation and fibrosis. Certain patterns are strongly associated with specific types of ILD; for instance, a “honeycombing” pattern is a classic sign of idiopathic pulmonary fibrosis.
Pulmonary function tests (PFTs) are also conducted to assess how well the lungs are working. These breathing tests use a spirometer to measure lung capacity and how efficiently air can be moved. Another part of PFTs, the diffusion capacity test, measures how effectively oxygen is transferred from the air sacs into the bloodstream. In ILD, these tests show a restrictive pattern (meaning the lungs hold less air than normal) and a reduced diffusion capacity.
Invasive Diagnostic Procedures
When information from non-invasive tests does not lead to a confident diagnosis, more direct methods may be required. These invasive procedures are reserved for complex cases where a closer look at lung tissue or cells is necessary to distinguish between different types of ILD. The decision to proceed weighs the benefits of a definitive diagnosis against the potential risks.
One such procedure is a bronchoscopy, where a physician inserts a thin, flexible tube with a camera through the nose or mouth and into the airways for visual inspection. During the bronchoscopy, a technique called a bronchoalveolar lavage (BAL) is often performed. This involves washing a small section of the lung with a sterile saline solution and then suctioning the fluid back out. The collected fluid contains cells from the air sacs, which can be analyzed in a laboratory.
In cases where a BAL does not provide a clear answer, a surgical lung biopsy may be recommended. This procedure involves the surgical removal of small samples of tissue from one or more areas of the lung. A pathologist then examines the tissue under a microscope to see the exact pattern of fibrosis and inflammation, which is often the only way to confirm a specific type of ILD.
Finalizing the Diagnosis
The final step in the diagnostic process is a synthesis of all the information gathered, as a diagnosis is rarely made from one piece of evidence alone. It relies on the consideration of every detail, from symptoms and exposures to the patterns on an HRCT scan and the details from a biopsy. To ensure the most accurate diagnosis, this information is reviewed in a multidisciplinary discussion (MDD).
This is a collaborative meeting where a team of specialists convenes to discuss the case. This team includes a pulmonologist, a radiologist, and a pathologist. By combining their expertise, the team can deliberate on the findings, discuss differing interpretations, and reach a consensus on the final diagnosis. This collaborative approach is considered the gold standard for diagnosing ILD because of the complexity and variety of these diseases. The goal of this process is to identify the specific type of the disease to select the most effective course of treatment.