Is interstitial lung disease a large category of diseases? How is it diagnosed and treated?

Author: Fang Baomin, Chief Physician, Beijing Hospital

Reviewer: Zhi Xiuyi, Chief Physician, Xuanwu Hospital, Capital Medical University

Lung tissue is divided into two parts: parenchyma and interstitium. Parenchyma refers to the branches of the bronchial tubes at all levels in the lungs and the large number of alveoli at their terminals. Interstitium refers to the supporting tissues between alveoli and outside the epithelium of the terminal airways, including connective tissue, blood vessels, lymphatic vessels, nerves, etc.

Interstitial lung disease is a large group of diseases, with more than 200 types so far. Due to various reasons, the main characteristics of the lung interstitium are inflammation and fibrosis. The main clinical manifestations are cough and progressive dyspnea. If not treated in time, it will eventually develop into respiratory failure and lead to death. It is a large category of diseases that threaten human health.

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The causes of interstitial lung disease are many and complex. Generally speaking, there are several reasons.

First, it is related to inhaled dust. Inhaled dust is generally organic, and some are inorganic. After the organic matter is inhaled into the lungs as an antigen, the body will produce an antigen-antibody reaction, resulting in the so-called interstitial changes. Of course, there are individual differences, and some people are not likely to get it even if they inhale dust.

Second, granulomatous diseases, with granuloma as the main manifestation, can appear as pulmonary nodule-like shadows, ground-glass shadows, and reticular shadows.

Third, connective tissue diseases refer to autoimmune diseases involving connective tissue. This type of disease accounts for a relatively high proportion, such as Sjögren's syndrome, rheumatoid arthritis, etc., which can easily induce interstitial lung disease.

Fourth, it may be related to genetics. For example, familial idiopathic pulmonary fibrosis and some interstitial pneumonias with unknown causes have a tendency to cluster in families, but the clear genetic path or genetic gene phenotype is not yet clear. There is a certain genetic tendency, but the proportion is not very high.

Fifth, diffuse manifestations of both lungs, such as alveolar proteinosis, pulmonary Langerhans' histiocytosis, etc., can all manifest as diffuse lesions in both lungs.

Sixth, when the cause cannot be found, it is called idiopathic interstitial lung disease.

Symptoms of interstitial lung disease may also appear before the diagnosis of infection or tumor is clear. In addition, one type of interstitial lung disease is closely related to smoking, such as desquamative interstitial pneumonia, respiratory bronchiolitis with interstitial lung disease, pulmonary Langerhans histiocytosis, etc. Idiopathic pulmonary fibrosis is also related to smoking.

The main clinical manifestations of interstitial lung disease are cough and shortness of breath after activity. In the early stage, it manifests as cough, which is often an irritating dry cough without sputum. Shortness of breath after activity is progressively aggravated. In the early stage, you will feel chest tightness and shortness of breath during activities. As time goes by, you will feel chest tightness and shortness of breath with just a little activity, even if it is not strenuous. In the late stage, you will also feel chest tightness and shortness of breath in a quiet state. This situation is called progressive dyspnea.

Because there are inflammatory cells, edema, and thickening of fibroblasts in the pulmonary interstitium, the lungs lose their elasticity and gases cannot be exchanged normally, which manifests as difficulty breathing.

If you have been coughing for a long time, such as more than a month, or have symptoms of chest tightness and shortness of breath, it is recommended to go to the hospital for examination in time, mainly for chest imaging examination, such as chest CT, which mainly shows ground-glass shadows, lattice shadows, and cystic changes. Based on imaging examinations, combined with serological tests, a diagnosis can usually be made.

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However, for a considerable number of patients, serological and imaging tests still cannot confirm the diagnosis, and further tests are needed, such as bronchoscopic lavage, and taking out the lavage fluid for testing. In addition, lung tissue biopsy can be taken through bronchoscopy for pathological examination. If the diagnosis is still not clear, the only option is to open the chest for lung biopsy.

Interstitial lung disease is characterized by inflammation and fibrosis. From a pathological point of view, interstitial lung disease can be divided into three types: one is dominated by inflammatory cell infiltration, the second is dominated by fibrosis, and the third is both inflammatory cell infiltration and fibrosis.

Inflammatory cell infiltration is the main problem, and the use of glucocorticoids and immunosuppressants is very effective. In fibrosis, fibroblasts produce collagen, and collagen fibers are deposited in the lung interstitium, causing the lung tissue to harden. In this case, the treatment effect is generally not ideal because the use of glucocorticoids and immunosuppressants is not very effective. Inflammatory cell infiltration and fibrosis components are present, and the inflammatory cells can be eliminated through treatment, and the condition can be alleviated or stabilized.

For example, idiopathic interstitial pneumonia, connective tissue disease combined with interstitial lung disease, sarcoidosis, exogenous allergic alveolitis caused by inhalation, etc., all require the use of glucocorticoids and immunosuppressants for treatment, and the treatment is still effective. There is also a large category such as pulmonary alveolar proteinosis, which cannot use hormones and requires alveolar lavage to clean out the deposits in the alveoli. For idiopathic pulmonary fibrosis, the use of glucocorticoids and immunosuppressants is ineffective so far. The currently recommended treatment drugs are small molecule compounds, which can only delay the progression of the disease, but cannot reverse it or cure it.

Interstitial lung disease is treated with hormones and immunosuppressants. Although some of them have a better prognosis, there is still a possibility of recurrence. The recurrence rate of different diseases is different.