Autoimmune diseases develop when the immune system, designed to attack foreign invaders, mistakenly targets and attacks the body’s own healthy tissues. This misdirected response can affect nearly any organ system, including the lungs. When the lungs are targeted, the resulting inflammation and damage interfere with the body’s ability to take in oxygen and function properly. Lung involvement is a complication of many systemic autoimmune conditions, sometimes appearing before the primary disease is diagnosed.
How Autoimmunity Damages Lung Tissue
The immune system’s attack on the lungs primarily results in two distinct types of injury: vasculitis and interstitial lung disease (ILD). Vasculitis involves inflammation and damage to the small blood vessels, which can lead to bleeding. This condition is known as diffuse alveolar hemorrhage (DAH), where blood pools in the tiny air sacs (alveoli), severely impairing gas exchange.
Chronic inflammation is the other major mechanism, causing scarring known as fibrosis. This scarring occurs in the interstitium, the delicate tissue surrounding the air sacs, and is termed ILD. As flexible lung tissue is replaced by stiff scar tissue, the lungs lose their ability to expand and efficiently transfer oxygen into the bloodstream.
Major Autoimmune Diseases Affecting the Lungs
Many systemic autoimmune diseases can involve the respiratory system, but some frequently cause significant lung complications.
Rheumatoid Arthritis (RA)
RA is best known for causing joint inflammation, but it is one of the most common causes of autoimmune-related ILD. Approximately 10% of people with RA develop clinically significant interstitial lung disease, often exhibiting a scarring pattern called Usual Interstitial Pneumonia (UIP).
Systemic Lupus Erythematosus (SLE)
SLE (lupus) is a multisystem disease where pulmonary involvement is frequent, affecting the pleura, airways, and lung tissue. While ILD is a concern, SLE more commonly causes pleuritis, which is inflammation of the lining around the lungs, leading to chest pain and fluid accumulation. Acute lupus pneumonitis, a sudden inflammation of the lung tissue, also occurs, and some patients experience “shrinking lung syndrome.”
Granulomatosis with Polyangiitis (GPA)
GPA, formerly known as Wegener’s, is a type of vasculitis that directly targets small blood vessels throughout the body. In the lungs, GPA can cause nodules, inflammation, and diffuse alveolar hemorrhage. This disease is part of a group called ANCA-associated vasculitides, characterized by specific autoantibodies.
Identifying Autoimmune Lung Involvement
Indications of autoimmune lung involvement often include a persistent, dry cough and increasing shortness of breath, particularly during physical activity. These symptoms can emerge slowly as scarring progresses, or they may appear suddenly in cases of acute inflammation or bleeding. In severe vasculitis, an individual may cough up blood, a symptom known as hemoptysis.
To confirm lung involvement, doctors use a combination of imaging and laboratory tests. High-resolution computed tomography (HRCT) scans provide detailed pictures of the lung structure to identify patterns of inflammation or scarring. Blood tests look for autoantibodies and inflammatory markers to confirm an underlying autoimmune condition. Pulmonary function tests (PFTs) measure lung capacity and oxygen transfer effectiveness, quantifying the extent of the damage.
Treatment Strategies for Autoimmune Lung Conditions
Management focuses on two objectives: suppressing the overactive immune system and providing supportive care for damaged lung tissue. Immunosuppressive medications are the standard first line of treatment, aiming to halt the inflammation causing lung injury.
Immunosuppressive Therapy
This category includes corticosteroids (e.g., prednisolone), which are powerful anti-inflammatory agents used to quickly control the disease. Other immunosuppressants, such as mycophenolate mofetil or cyclophosphamide, are used to maintain control and reduce the need for high-dose steroids. Targeted therapies, known as biologics (e.g., rituximab), are employed to specifically target the immune cells responsible for the damage.
Supportive Care
For irreversible scarring (fibrosis), antifibrotic drugs like nintedanib can slow the rate of disease progression, often used with immunosuppressants. Supportive care, including supplemental oxygen therapy and pulmonary rehabilitation, helps patients manage breathing difficulties and maximize remaining lung function.