What Autoimmune Diseases Affect the Lungs?

A surprisingly large number of autoimmune diseases can damage the lungs, and interstitial lung disease is the most common way they do it. Systemic sclerosis, rheumatoid arthritis, inflammatory myopathies, lupus, Sjögren’s syndrome, and several forms of vasculitis all carry real risk of lung involvement, though the likelihood and severity vary enormously from one condition to another. In some of these diseases, lung problems develop quietly over years; in others, they can arrive within weeks and become life-threatening before the underlying autoimmune condition is even diagnosed.

Interstitial Lung Disease as the Common Thread

The term interstitial lung disease, or ILD, refers to a group of conditions in which inflammation or scarring builds up in the tissue between the air sacs of the lungs. That tissue is where oxygen passes into the bloodstream, so damage there makes it progressively harder to breathe. When autoimmune diseases affect the lungs, ILD is by far the most frequent pattern. The prevalence varies dramatically depending on which autoimmune disease you have. Roughly 44 to 50% of people with systemic sclerosis develop ILD, and 33 to 50% of people with certain subtypes of inflammatory myopathy do as well. For rheumatoid arthritis the figure is closer to 7 to 15%, and for lupus it drops to about 3 to 10%.¹ Whatever the underlying disease, developing ILD worsens the prognosis considerably.

Not all autoimmune lung damage looks the same under a CT scan or a microscope, and those differences matter for predicting what happens next. Two broad patterns dominate. One, called usual interstitial pneumonia or UIP, tends to produce a honeycomb-like scarring pattern in the lower parts of the lungs. The other, called nonspecific interstitial pneumonia or NSIP, produces more of a hazy “ground-glass” appearance without the honeycombing.² The UIP pattern generally carries a worse outlook, as discussed below for specific diseases.

Systemic Sclerosis

Systemic sclerosis, also called scleroderma, is the autoimmune disease most likely to involve the lungs. Up to half of all patients develop ILD, and about two-thirds of those with scleroderma-related ILD see their lung disease progress over five years.¹ The disease causes widespread fibrosis, and the lungs are one of its primary targets. Screening with high-resolution CT scanning is important early on, because lung function tests alone can miss the problem. In one study of patients with early diffuse scleroderma, more than a third of those who had ILD visible on CT scan still had normal-looking lung function numbers.³

Scleroderma also threatens the lungs in a second, distinct way: pulmonary arterial hypertension, which is abnormally high blood pressure in the arteries connecting the heart and lungs. This affects roughly 8 to 15% of scleroderma patients and can occur in both the limited and diffuse forms of the disease.⁴ These are two separate problems. A patient with scleroderma can develop ILD alone, pulmonary hypertension alone, or both at once. Each requires different treatment strategies, so distinguishing between them is clinically important.

Rheumatoid Arthritis

Rheumatoid arthritis is best known for attacking joints, but lung involvement is more common than many patients realize. Somewhere between 7 and 15% of people with rheumatoid arthritis develop clinically significant ILD, and the number is higher when you count subclinical cases found incidentally on imaging.¹ The UIP pattern shows up frequently in rheumatoid arthritis-associated ILD and predicts worse survival compared to the NSIP pattern. Patients with UIP-pattern disease have a median survival of around 3.2 years, compared with about 6.6 years for those with a non-UIP pattern.²

Identifying the UIP pattern on CT scans is especially important because patients with either definite or possible UIP have equally poor outcomes, meaning even an uncertain UIP appearance should raise alarms.⁵ This also makes the clinical course resemble idiopathic pulmonary fibrosis, the most common and severe form of ILD in the general population. Episodes of sudden worsening, called acute exacerbations, can happen in both conditions.² Risk factors that raise the chances of developing lung disease in rheumatoid arthritis include older age, male sex, and a history of smoking, which is notable because rheumatoid arthritis itself is more common in women.³

Inflammatory Myopathies and the Anti-MDA5 Problem

Inflammatory myopathies, especially dermatomyositis, are conditions best known for causing muscle weakness and skin rashes. But they rank second only to scleroderma in how often they produce ILD, with 33 to 50% of certain subtypes developing lung involvement.¹ The scariest version of this is driven by a specific autoantibody called anti-MDA5. Patients who carry this antibody can develop rapidly progressive ILD that worsens over weeks, not months or years, and carries impressively high mortality.⁶

What makes anti-MDA5-positive dermatomyositis especially tricky is that the muscles are sometimes barely affected. Patients with the “clinically amyopathic” form may have skin rashes and devastating lung disease but almost no muscle weakness, which can delay a correct diagnosis.⁷ In rare cases, even the characteristic skin findings are absent. This condition has been predominantly reported in East Asian populations, though it is recognized worldwide.⁶ Recognizing it quickly is essential because aggressive immunosuppressive treatment started early can be life-saving.

Lupus and the Shrinking Lung Syndrome

Systemic lupus erythematosus, or lupus, can affect the lungs in several ways. ILD develops in about 3 to 10% of patients, making it less common than in scleroderma or myositis but still clinically relevant.¹ Pleuritis, or inflammation of the membrane surrounding the lungs, is actually more frequent and causes the sharp chest pain many lupus patients recognize. But the most distinctive lung problem in lupus is something called shrinking lung syndrome.

Shrinking lung syndrome shows up as progressive shortness of breath with exertion, rapid shallow breathing, and a striking limitation in how far the chest wall can expand. Patients breathe in a labored, accessory-muscle-heavy way and eventually become breathless even at rest.⁸ The mechanism has been debated for decades. Early thinking focused on diaphragm weakness, and some patients do show reduced pressure-generation capacity. However, careful measurements using phrenic nerve stimulation have shown that the diaphragm itself is structurally normal in most patients with this syndrome. The reduced function appears to stem from incomplete voluntary activation of the diaphragm rather than from a primary muscle or nerve problem.⁹ In other words, the nerve signals telling the diaphragm to contract appear intact, and the muscle itself is capable of normal force. Something upstream is interfering with how the brain recruits the diaphragm during breathing efforts.¹⁰

Sjögren’s Syndrome

Sjögren’s syndrome is mostly known for dry eyes and dry mouth, caused by immune cells infiltrating the glands that produce moisture. Those same immune cells can infiltrate the lungs as well, and roughly 12 to 21% of patients with primary Sjögren’s develop ILD.¹ The lung involvement in Sjögren’s has a particular character. The dryness component can directly damage airways by reducing the moisture that normally protects the trachea and bronchi. On top of that, immune cells can infiltrate the airway walls and the tissue between the air sacs.¹¹

One specific pattern, called lymphocytic interstitial pneumonia or LIP, has a notable association with Sjögren’s and accounts for about 15% of ILD cases in these patients. LIP produces cough and shortness of breath along with distinctive CT findings including ground-glass haziness, nodules, and thin-walled cysts visible in the majority of patients. The concern with LIP is that persistent lymphocyte accumulation in the lungs can, in rare cases, evolve into lymphoma, so biopsy and ongoing monitoring are important.¹¹ Even patients without obvious respiratory symptoms have been found to harbor immune cell infiltration of the bronchial tissue on biopsy, suggesting that airway involvement in Sjögren’s may be more widespread than symptoms alone would indicate.¹²

Vasculitis and Bleeding Into the Lungs

The ANCA-associated vasculitides, a group of diseases that inflame small blood vessels, affect the lungs differently from the conditions discussed so far. Rather than primarily causing fibrosis, they tend to damage lung blood vessels directly. One of the most serious complications is diffuse alveolar hemorrhage, where widespread bleeding into the air sacs produces cough, bloody sputum, rapid onset of breathing difficulty, and falling oxygen levels.¹³ This is a medical emergency requiring immediate immunosuppression and sometimes plasma exchange.

ANCA-associated vasculitis can also produce ILD, with estimates ranging from 2 to 25% of patients.¹ The wide range reflects differences across the three main subtypes and how actively clinicians look for it. Goodpasture syndrome, a rarer condition caused by antibodies that attack the basement membrane shared by the lungs and kidneys, can produce a similar hemorrhagic picture. The classic presentation involves a young person developing both kidney failure and lung bleeding simultaneously, though not every patient gets both organs involved.

Treatment Approaches

Treating autoimmune lung disease generally involves two goals: quieting the immune attack causing the damage, and slowing fibrotic progression once scarring has started. Immunosuppressive drugs such as mycophenolate remain a mainstay for many forms of autoimmune-related ILD. Rituximab, which depletes a specific type of immune cell, has been tried for cases that do not respond to standard treatment. In patients with stubborn disease, adding rituximab to mycophenolate did not significantly improve lung function test numbers, but it did allow patients to reduce their steroid doses, which matters for avoiding the side effects of long-term steroid use.¹⁴

On the antifibrotic side, nintedanib has shown consistent ability to slow the decline in lung function across different types of progressive fibrotic lung disease, including autoimmune-related forms. The drug does not reverse existing damage, but it slows the rate at which breathing capacity drops.¹⁵ This distinction is worth understanding: patients sometimes expect these medications to restore their lung function, when the realistic goal is to keep it from deteriorating as fast. For end-stage disease that continues progressing despite therapy, lung transplantation remains an option, though it carries its own set of complications.

When the Treatment Itself Causes Lung Problems

One of the more frustrating aspects of autoimmune lung disease is that some medications used to treat the underlying condition can also harm the lungs. Methotrexate, a cornerstone drug for rheumatoid arthritis, can cause a drug-induced lung inflammation called methotrexate pneumonitis. This can mimic the symptoms and imaging findings of rheumatoid arthritis-associated ILD, making the two difficult to tell apart. One important clue is timing: methotrexate pneumonitis tends to come on acutely, while autoimmune-related ILD develops more gradually. If older imaging shows early changes that predate methotrexate use, that argues strongly for the autoimmune disease itself being the culprit.¹⁶

Getting this distinction right has real consequences. If methotrexate is causing the problem, stopping the drug is the fix. If autoimmune ILD is the real diagnosis and you blame the drug, the patient loses an effective therapy for their arthritis. Rheumatologists and pulmonologists often need to work together on these cases, and having earlier baseline imaging of the lungs can make the puzzle much easier to solve.

Pregnancy and Autoimmune Lung Disease

ILD showing up during pregnancy is rare, but when it does, the stakes are high for both the mother and the baby. Pregnancy naturally increases the body’s demand for oxygen and puts extra strain on the cardiovascular system, which magnifies the impact of any existing lung impairment. Reports have linked autoimmune-related ILD during pregnancy with higher rates of preeclampsia, preterm birth, and fetal loss.¹⁷

The severity of lung disease appears to be a major driver of outcomes. In one study, adverse pregnancy outcomes occurred in all pregnancies among women with very severe ILD, compared to fewer than half in women with milder disease. Women with connective tissue disease-related ILD had worse outcomes than those with sarcoidosis-related ILD specifically.¹⁸ Treatment options during pregnancy are limited because many standard immunosuppressants carry risks for fetal development, though individual drugs like tacrolimus and corticosteroids have been used successfully under close monitoring.¹⁷

How Breathlessness Shapes Daily Life

The numbers and disease patterns above can obscure what autoimmune lung disease actually feels like. The defining symptom is breathlessness, which starts with exertion and can eventually limit everything from climbing stairs to getting dressed. In patients with connective tissue disease-related ILD, the degree of breathlessness predicts not only physical limitations but also psychological well-being and fatigue, independently of how severe the lung disease looks on imaging or pulmonary function tests.¹⁹ Two people with similar-looking CT scans can have very different levels of disability depending on how breathless they feel. This has practical implications for treatment decisions, because subjective breathlessness is sometimes a better indicator of how much a patient’s life is affected than the objective measurements clinicians tend to prioritize.

The overlap of joint pain, fatigue, and breathing difficulty creates a layered burden. A person with rheumatoid arthritis and ILD is not just dealing with one chronic disease but with the compounding effects of two systems under attack. Depression and anxiety rates are elevated in these populations, and exercise capacity drops further when joint disease limits the compensatory strategies people use to cope with shortness of breath.

The Gut-Lung Axis

One of the more unexpected research threads involves the relationship between gut bacteria and lung disease. Researchers have identified a communication network between the gastrointestinal tract and the lungs, sometimes called the gut-lung axis, in which changes in gut microbial communities can influence immune behavior and inflammation in the airways.²⁰ Disruptions to the gut microbiome have been linked to altered immune responses that could, in theory, promote the kind of immune dysregulation seen in autoimmune ILD. This is still an early-stage area of research, and nobody is recommending probiotics as ILD treatment. But it represents a shift in how scientists think about what drives these diseases, moving beyond the lungs themselves to consider systemic factors that might make the immune system more likely to go wrong in the first place.

CAR T-Cell Therapy for Autoimmune Disease

On the cutting edge, researchers have begun applying CAR T-cell therapy, a technique originally developed for blood cancers, to autoimmune diseases. This involves engineering a patient’s own immune cells to target and eliminate the B cells that produce harmful autoantibodies. Early-stage applications have been tried in lupus, inflammatory myopathy, systemic sclerosis, and several other autoimmune conditions.²¹ The results from initial case series, particularly in lupus and myositis, have generated genuine excitement, with some patients achieving drug-free remission. Whether this translates into meaningful improvement in established lung fibrosis remains an open question. Scar tissue in the lungs does not reverse easily regardless of how thoroughly you shut off the immune attack causing it, so the greatest benefit may be for patients treated before significant scarring develops. The logistics are also formidable: CAR T-cell therapy requires specialized manufacturing, carries risks of serious immune reactions, and remains extremely expensive. For now, it is a proof of concept rather than a widely available treatment, but it represents perhaps the most fundamental rethinking of autoimmune treatment strategy in a generation.

1
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13
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15
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16
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17
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18
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21
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