An autoimmune disease develops when the immune system mistakenly targets healthy tissues, causing chronic inflammation and systemic damage. The lungs are a frequent and serious site of involvement, sometimes being the first organ affected. Pulmonary involvement ranges from inflammation and scarring of lung tissue to damage of the tiny blood vessels. Understanding the major categories of autoimmune diseases that affect the lungs is important.
Connective Tissue Diseases and Pulmonary Manifestations
Connective Tissue Diseases (CTDs) target structural proteins like collagen and elastin. Since the lungs rely heavily on this framework, they are a common target for damage in conditions like Rheumatoid Arthritis (RA), Systemic Lupus Erythematosus (SLE), and Systemic Sclerosis (SSc). The most frequent manifestation is Interstitial Lung Disease (ILD), involving inflammation and scarring of the tissue surrounding the air sacs.
In SSc, ILD affects up to 50% of patients, often presenting as Non-Specific Interstitial Pneumonia (NSIP) or Usual Interstitial Pneumonia (UIP). RA also commonly causes ILD, sometimes before joint symptoms appear. This scarring, or pulmonary fibrosis, impairs oxygen transfer, leading to shortness of breath and a persistent dry cough.
Less commonly, these diseases can cause fluid accumulation in the lining around the lungs, known as pleural effusions. RA can also lead to the formation of rheumatoid nodules, which are inflammatory tissue lumps in the lung. These pulmonary issues typically result in progressive stiffening and reduced lung capacity over time.
Autoimmune Vasculitides Targeting the Respiratory System
Autoimmune lung disease also involves the vasculitides, characterized by inflammation of the blood vessels. This inflammation restricts blood flow and damages tissues, leading to pulmonary symptoms different from those seen in CTDs. The size of the affected vessels determines the specific respiratory manifestation.
Granulomatosis with Polyangiitis (GPA) affects small to medium-sized blood vessels and is linked to the ANCA autoantibody. GPA often causes inflammatory masses or nodules in the lungs, which can sometimes form cavities. A severe complication is diffuse alveolar hemorrhage, where inflammation of the small lung vessels causes bleeding into the air sacs.
Eosinophilic Granulomatosis with Polyangiitis (EGPA) involves a high number of eosinophils. Individuals with EGPA often have a history of severe or newly developed asthma. Pulmonary symptoms include difficult-to-control asthma and transient lung infiltrates. Vasculitides primarily attack the circulatory framework of the lung, leading to rapid-onset problems like bleeding or severe asthma.
Identifying Autoimmune Lung Disease
Diagnosing an autoimmune lung condition requires differentiating it from infections and other disorders. The initial workup involves imaging, function tests, and blood analysis. High-Resolution Computed Tomography (HRCT) scanning is the most sensitive imaging tool, providing detailed images to identify scarring, inflammation, or nodules.
Pulmonary Function Tests (PFTs) measure lung capacity, often revealing a restrictive pattern characteristic of ILD. PFT results also show reduced capacity for gas exchange, reflecting damage to the air sacs. Specific blood work detects autoantibodies, such as Antinuclear Antibodies (ANA), Rheumatoid Factor (RF), and ANCA, indicating an underlying autoimmune condition.
While non-invasive tests strongly suggest a diagnosis, a lung biopsy may be necessary to confirm the specific pattern of injury and rule out other causes. A multidisciplinary team of specialists reviews the findings to ensure the most accurate diagnosis.
Managing Autoimmune-Related Lung Damage
Management focuses on controlling immune hyperactivity and reducing inflammation to slow lung damage. The primary approach uses immunosuppressive medications, such as corticosteroids, which quickly decrease inflammation. These are often paired with steroid-sparing agents, like azathioprine or mycophenolate mofetil, for long-term control.
Targeted biologic therapies suppress specific immune components, such as B-cells or inflammatory proteins. Rituximab, a B-cell targeting agent, has demonstrated effectiveness in stabilizing lung function in some patients with CTD-ILD. When lung scarring (fibrosis) is the dominant problem, anti-fibrotics may be used to slow the rate of decline.
Supportive care is necessary, especially as the disease impairs oxygen exchange. This includes supplemental oxygen therapy and pulmonary rehabilitation, a structured program designed to improve quality of life. Regular monitoring using PFTs and HRCT scans is essential to track the disease’s course and adjust the treatment strategy.