What is interstitial lung disease
Interstitial lung disease is a lung disease characterized by extensive destruction of the alveolar wall, loss of functional alveolar capillary units, and accumulation of collagen scar tissue. As the destruction of interstitial lung structures directly affects alveolar-capillary gas exchange, it leads to respiratory dysfunction with hypoxia as the main manifestation.
Guo Qiang, Department of Rheumatology, Shanghai Renji Hospital
Dangers of interstitial lung disease
Almost all patients with interstitial lung disease suffer from reduced exercise tolerance and progressive respiratory dysfunction. Not only does daily life suffer significantly, but an ordinary respiratory infection can become intolerable for the patient and even lead to catastrophic results.
Etiology of interstitial lung disease
Interstitial lung disease is not just one disease, but includes a group of lower respiratory tract diseases with similar characteristics. Some of them are genetically related, such as tuberous sclerosis; some are related to exposure to harmful substances, such as smoking, dust inhalation, chemotherapy, and contraband exposure; some are related to infections, such as viral, mycoplasma, mycobacterial, and bacterial infections; and some are related to certain diseases, such as rheumatism and lymphangioleiomyomatosis.
Rheumatic disease and interstitial lung disease
Compared to disseminated cases related to infections and exposure to harmful substances, patients with rheumatologic diseases are more concentrated with interstitial lung disease, which can reach 1/3 proportion of the overall patients. Therefore, screening for the latent presence of rheumatic diseases is extremely important for patients with interstitial lung disease. Rheumatic diseases that are likely to complicate interstitial lung disease include scleroderma, dermatomyositis, polymyositis, mixed connective tissue disease, systemic vasculitis, rheumatoid arthritis, systemic lupus erythematosus, and dry syndrome. Patients who are clearly suffering from these rheumatic diseases should not neglect screening for interstitial lung disease.
Pathogenesis of interstitial lung disease
Interstitial lung disease is the result of a combination of tissue damage, inflammation, and repair insufficiency. Tissue injury secondary to inflammation, when the direct injury to the lung caused by pathogens or toxic agents is too strong or the inflammation triggered cannot be self-limited and continues to develop, the normal repair process is disturbed and pro-fibrotic factors take over, leading to excessive deposition of fibroblasts and collagen, components that were not dominant in the interstitial lung matrix, thus causing interstitial lung disease.
Clinical manifestations of interstitial lung disease
Dyspnea is the most common symptom of this type of lung disease. It initially occurs only with exertion and is often attributed to other causes such as viral infections, cardiac insufficiency, and poor physical fitness, and as the disease progresses eventually dyspnea may also occur at rest. Dry cough and fatigue are also more common symptoms. Mortar and pestle fingers/toes are a common sign of interstitial lung disease, manifested as hyperplasia of the ends of the fingers and/or toes, but are not unique to the disease and can be seen in hypertrophic osteoarthrosis and pulmonary malignancies. Another common sign of interstitial lung disease is bilateral basilar twisting of the lungs. In the early stages of the disease, the heart examination is normal, but in the late stages, tachycardia may be present. When complicated by pulmonary hypertension there may be a heart murmur and swelling of the lower extremities.
How to perform early screening for interstitial lung disease
Chest X-ray is the traditional screening method for interstitial lung disease, and early detection of interstitial lung disease is difficult due to low resolution. Therefore, early screening relies most heavily on high-resolution thin-layer computed tomography (HRCT) of the chest and pulmonary diffusion function tests.
Significance of pulmonary function tests
Although not very helpful in identifying the cause, pulmonary function tests are sensitive to changes in respiratory function due to various lung diseases, and they are harmless to the subject, so they are an important tool for assessing the effectiveness of treatment and can be repeated over a short period of time. Typical changes in pulmonary function in interstitial lung disease are reduced total lung capacity (TLC), reduced carbon monoxide dispersion (DLco), and a higher than normal ratio of forceful expiratory volume in one second (FEV1) to maximum expiratory volume (FVC).
Significance of high-resolution CT of the lungs
High-resolution CT (HRCT) can detect lesions early that cannot be detected by conventional chest X-ray, make quantitative assessment of the extent of lesions and fibrosis, and determine the appropriate sampling site for bronchoscopy or lung tissue biopsy.
Significance of bronchoscopy
Interstitial lung disease detected by HRCT and lung function screening needs to be differentiated from infections and tumors, and the exact cause of the interstitial lung disease itself needs to be further defined. Bronchoscopy allows observation of lesions in the large airways and access to lavage fluid and adjacent tissue specimens, and is an important tool not only for establishing lung diseases such as eosinophilic pneumonia, alveolar protein deposition, hemorrhagic alveolitis, and histiocytosis X, but also for searching for possible co-infections and identifying latent tumors.
What to look for after a definite diagnosis
Avoid exposure to harmful substances, including quitting smoking; prevent respiratory infections and stay away from places where germs can be easily spread; communicate closely with your doctor and develop a treatment plan together; use drugs that can cause interstitial lung disease with caution; and follow up regularly with lung function and chest HRCT.
Can interstitial lung disease be cured?
Interstitial lung disease is the result of lung tissue damage that has not been effectively repaired. If the factors of damage can be eliminated as soon as possible and the unfavorable factors of repair can be eliminated more easily, there is hope for a cure. At present, most patients have developed and accumulated lesions by the time the diagnosis is established, and some have entered the fibrosis stage and are difficult to cure completely. The prerequisite for an improved prognosis is early diagnosis and treatment. Early clinical manifestations of interstitial lung disease should not be ignored, and once symptoms such as abnormal reduced exercise tolerance, dyspnea, and dry cough appear, prompt medical attention should be sought to screen for interstitial lung disease through pulmonary function and chest HRCT.