Diffuse interstitial lung disease refers to a large group of lung disorders that affect the interstitium, which is the connective tissue that forms the support structure of the alveoli (air sacs) of the lungs. Normally when you inhale, the alveoli fill with air and oxygen passes into the blood stream. When you exhale, carbon dioxide passes from the blood into the alveoli and is then expelled from the body. When interstitial disease is present, the lung becomes inflamed and stiff, preventing the alveoli from fully expanding. This limits both the delivery of oxygen to the blood stream and the removal of carbon dioxide from the body. As the disease progresses, the interstitium and the walls of the alveoli thicken, which further impedes lung function.
Blood tests, pulmonary function tests (spirometry), pulse oximetry, chest x-ray, chest CT, bronchoscopy with biopsy, or surgical biopsy may be performed to help diagnose your condition. Treatment may depend on the underlying cause of the disease and your health status. Medication, respiratory therapy or surgery may be prescribed to help improve lung function.
What is diffuse interstitial lung disease?
Diffuse interstitial lung disease (ILD) is a group of disorders that affect the connective tissue (interstitium) that forms the support structure of the alveoli (air sacs) of the lungs.
In a normal lung, the alveoli fill with air during inhalation. Oxygen within the air passes through the walls of the alveoli into the blood stream. In reverse fashion during exhalation, carbon dioxide passes from the blood into the alveoli. When affected by an interstitial lung disease, the tissue supporting the alveoli becomes inflamed and stiff, which makes it difficult for the alveoli to fully expand. The abnormal interstitium limits the delivery of oxygen to the body and the removal of carbon dioxide from the body. As interstitial disease progresses, the supporting tissue scars and thickens the alveolar walls, further decreasing lung function. In some cases, inflammation may be confined to one or more areas of the lung. However, it is frequently diffuse, meaning it occurs throughout both lungs.
Interstitial lung diseases can be grouped based on cause, association with other diseases, or pathology. Interstitial lung disease may be associated with autoimmune or inflammatory diseases such as:
- rheumatoid arthritis
- scleroderma (systemic sclerosis)
- polymyositis and dermatomyositis (an inflammatory disease that causes muscle weakness)
- inflammatory bowel disease
It may also be caused by exposure to drugs, such as:
- chemotherapy agents
- antiarrythmics (used to treat irregular heart rhythm)
- statins (used to lower cholesterol levels)
It may also stem from the inhalation of substances, such as
- animal proteins
Interstitial lung disease related to the inhalation of cigarette smoke can occur as a spectrum of injury that includes respiratory bronchiolitis-interstitial lung disease and desquamative interstitial pneumonia.
In some cases, interstitial lung disease may be associated with a collection of inflammatory cells (granuloma), as is seen in sarcoidosis. Other diseases associated with inflammation include idiopathic pulmonary fibrosis (IPF), usual interstitial pneumonia (UIP), acute interstitial pneumonia (AIP), cryptogenic organizing pneumonia (COP) and non-specific interstitial pneumonia (NSIP). There are also many other causes of interstitial lung disease. In some cases, the cause of interstitial disease is also unknown. Occasionally, interstitial disease is associated with a familial cause or specific genetic disease.
The most common symptoms of diffuse interstitial lung disease are shortness of breath and dry cough. As the disease progresses, weight loss, muscle and joint pain, and fatigue may also occur. At a more advanced stage, individuals may develop an enlarged heart, enlargement of the fingertips clubbing), and cyanosis (blue coloration in the lips, skin and fingernails as a result of reduced oxygen levels in the blood). Individuals might also experience nonrespiratory symptoms, such as muscle pain, joint pain, or thickening or tightness of the skin, particularly in the presence of autoimmune disease.
How is diffuse interstitial lung disease diagnosed and evaluated?
To determine the cause of interstitial lung disease, a physician may perform a physical examination and order diagnostic tests, including:
- Blood tests: These tests may help identify autoimmune diseases, such as scleroderma and rheumatoid arthritis, which can be associated with interstitial lung disease.
- Spirometry: This is a test of lung function, in which the patient exhales quickly and forcefully through a tube connected to a machine that measures how much air the lungs can hold and how quickly the air moves in and out of the lungs. Spirometry can help determine if there is a problem getting air into the lungs (restriction, such as fibrosis) or out of the lungs (obstruction, such as asthma).
- Pulse oximetry: This test uses a small device placed on a finger tip to measure the oxygen saturation of the blood. It shines a specific wavelength of light though the end of the finger to painlessly measure the amount of oxygen.
- Chest x-ray: The patterns of lung damage associated with various types of interstitial lung disease are often identifiable on chest x-rays. Chest x-rays may also be used to track the progression of interstitial lung disease.
- CT imaging of the chest: : Computed tomography (CT), including a specific technique known as high resolution CT, is used to see fine detail of the interstitium that may not be visible on a chest x-ray . In some cases, a specific diagnosis (such as idiopathic pulmonary fibrosis) can be confirmed based on the CT appearance, potentially avoiding the need for lung biopsy. A CT scan can also often help determine the extent of damage to the lungs, guide biopsy when needed, and help determine appropriate treatment(s).
- Bronchoscopy and biopsy: In this procedure, a very small sample of tissue is removed from the lung using a small, flexible tube called a bronchoscope that is passed through the mouth or nose, down the trachea (windpipe) and into the lungs.
- Surgical biopsy: A surgical biopsy may be needed to obtain a larger tissue sample than is possible with bronchoscopy. During this procedure, surgical instruments and a small camera are inserted through two or three small incisions between ribs, allowing a physician to see and remove tissue samples from the lungs.
How is diffuse interstitial lung disease treated?
Treatment depends on the cause of the interstitial disease and the health status of the patient. Various drugs may be prescribed to reduce inflammation in the lungs and/or to suppress the immune system.
Oxygen or respiratory therapy may be offered to help improve lung function. Some patients with advanced lung disease may require a lung transplant.