Sarcoidosis of the lung, also called pulmonary sarcoidosis, is a condition where the immune system forms tiny clusters of inflammatory cells called granulomas in the lung tissue and surrounding lymph nodes. These granulomas can interfere with normal lung function, causing a persistent cough, shortness of breath, and chest pain. About 60% of all cases eventually resolve on their own, but the rest can become chronic and, in some cases, lead to permanent scarring of the lungs.
What Happens Inside the Lungs
Sarcoidosis begins when the immune system overreacts to a substance it cannot break down. Normally, immune cells called macrophages engulf and destroy foreign particles. In sarcoidosis, macrophages fail to eliminate the trigger and instead recruit more immune cells to the site. These cells cluster together into organized structures called granulomas, which are made up of macrophages, a type of white blood cell called CD4+ T lymphocytes, and smaller numbers of other immune cells and tissue-building cells.
Inside these granulomas, macrophages transform into specialized forms: epithelioid cells and multinucleated giant cells, which are essentially macrophages that have fused together. The granulomas in sarcoidosis are “non-caseating,” meaning they don’t develop the cheese-like dead tissue center seen in tuberculosis. This distinction is one of the key features doctors look for during diagnosis. When enough granulomas form in the lungs, they can disrupt airflow, reduce the lungs’ ability to exchange oxygen, and over time cause scarring.
What Causes It
The exact cause of pulmonary sarcoidosis remains unknown, but it likely results from a combination of genetic vulnerability and environmental exposure. Certain variations in immune system genes, particularly in a region called HLA on chromosome 6, significantly affect a person’s risk. One specific gene variant, HLA-DRB1*11:01, increases risk in both Black and white individuals, while other variants have race-specific effects. Interestingly, one variant (DRB1*03:01) increases disease risk in Europeans but is also linked to a higher chance of the disease resolving on its own.
On the environmental side, a large case-control study found modest increases in sarcoidosis risk among people who worked in agriculture, were exposed to insecticides, or worked in moldy or musty environments. Some of these exposures interact directly with specific genetic variants, suggesting the disease requires both the right genetic background and the right environmental trigger to develop.
There is also growing evidence pointing to certain bacteria. Proteins and genetic material from mycobacteria (relatives of the organism that causes tuberculosis) have been found in sarcoidosis tissue samples. A common skin bacterium, Propionibacterium acnes, has also been identified in affected tissue, with one analysis of nine studies showing a dramatically elevated risk of sarcoidosis in people carrying it. Still, no single microbe has been confirmed as the definitive cause.
Who Gets Pulmonary Sarcoidosis
Globally, about 4.6 million people were living with interstitial lung disease and pulmonary sarcoidosis in 2023, with an overall prevalence of roughly 50 per 100,000 people. Males have slightly higher rates than females (about 54 versus 48 per 100,000). The highest prevalence is in high-income Asia Pacific countries, where rates reach 155 per 100,000. In older adults, particularly those 65 and above, men consistently outnumber women in prevalence across all age groups. The disease is most commonly diagnosed between the ages of 25 and 50, though the highest total number of cases occurs in people aged 70 to 74.
Common Symptoms
Pulmonary sarcoidosis can be surprisingly quiet. Some people have no symptoms at all and only discover the condition when a chest X-ray taken for another reason reveals enlarged lymph nodes. When symptoms do appear, the most common respiratory complaints are a dry cough, shortness of breath, wheezing, and chest pain.
Beyond the lungs, sarcoidosis frequently causes systemic symptoms that can be just as disruptive. Fatigue is one of the most common and persistent complaints, often lingering even after lung involvement improves. Other general symptoms include unexplained weight loss, fever, night sweats, swollen lymph nodes, and depression. The disease can also affect the skin, producing rashes or firm lumps beneath the surface, and may involve the eyes, heart, nervous system, and joints.
How It Is Diagnosed
Diagnosing sarcoidosis requires three things: a clinical picture that fits (symptoms plus imaging findings), biopsy evidence showing the characteristic non-caseating granulomas, and ruling out other conditions that can look similar, like tuberculosis, fungal infections, or certain cancers.
A chest X-ray is usually the first step and is used to classify the disease into stages. A biopsy confirms the diagnosis in most cases, about 77% in one large series, while the remaining 23% are diagnosed based on a strongly suggestive clinical and imaging picture alone. Doctors aim to biopsy the most easily accessible site. That could be the skin, a swollen lymph node near the surface, or lymph nodes near the airways reached through a bronchoscope. For enlarged lymph nodes visible on imaging (common in early-stage disease), an ultrasound-guided needle biopsy through the airway has a diagnostic success rate of 80 to 90%.
Breathing tests can be normal early on or show different patterns of impairment. Reduced lung volumes (a restrictive pattern) are the most typical finding, but airflow obstruction, similar to what you’d see in asthma, occurs in about 25% of patients.
Stages of Lung Sarcoidosis
Doctors classify pulmonary sarcoidosis into five stages based on chest X-ray findings, using a system called the Scadding classification. These stages help predict outcomes more than they describe a strict progression, since many people never move from one stage to the next.
- Stage 0: Normal chest X-ray. The disease affects other organs but not the lungs or visible lymph nodes.
- Stage 1: Enlarged lymph nodes on both sides of the chest (bilateral hilar lymphadenopathy) without any visible lung involvement. About 90% of Stage 1 patients go into spontaneous remission.
- Stage 2: Enlarged lymph nodes plus abnormal patches in the lung tissue, typically in the upper lobes. Spontaneous remission occurs in 40 to 70% of cases.
- Stage 3: Lung tissue involvement without enlarged lymph nodes. Only 10 to 20% of patients at this stage experience spontaneous remission.
- Stage 4: Permanent lung scarring (pulmonary fibrosis). Spontaneous remission does not occur at this stage.
Outlook and Remission
The overall prognosis is favorable. Roughly 60% of all sarcoidosis cases resolve spontaneously, often within two to three years. Stage at diagnosis is the strongest predictor: the earlier the stage, the better the odds of the disease clearing on its own without treatment. For the remaining patients, sarcoidosis becomes a chronic condition that waxes and wanes, sometimes flaring when treatment is reduced.
The most serious long-term risk is progression to pulmonary fibrosis, where granulomatous inflammation is replaced by permanent scar tissue. Warning signs that the disease may be heading in this direction include shortness of breath at the time of first diagnosis, needing treatment right away, and requiring ongoing therapy for more than two years. Doctors monitor for progression by tracking lung function over time. A drop in lung capacity of 5% or more within a year, or a decline in the lungs’ ability to transfer oxygen of 10% or more, are criteria used to identify worsening fibrotic disease.
Treatment Approach
Not everyone with pulmonary sarcoidosis needs medication. Because roughly 30% of cases subside on their own without any treatment, doctors often start with a period of monitoring, especially for people with mild symptoms and early-stage disease. Treatment is reserved for situations where there is ongoing, worsening organ involvement or a real risk of permanent damage.
When treatment is needed, corticosteroids are the first choice. A starting dose of 20 mg daily of prednisone has been shown to work just as well as higher doses for controlling both new disease and flares of chronic disease. Major respiratory societies in Britain and Europe now recommend this moderate dose as the standard starting point. After three to six weeks, the dose is gradually lowered, with the goal of reaching a maintenance level of 5 to 10 mg daily by about six months. Treatment tends to be fairly prolonged to allow adequate suppression of the granulomatous inflammation.
The trade-off with long-term corticosteroids is a well-known list of side effects: weight gain, elevated blood sugar, bone thinning, cataracts, glaucoma, and mood changes including depression. These risks are why doctors aim for the lowest effective dose and why follow-up visits every three months are standard during treatment.
Options for Refractory Disease
For people whose sarcoidosis doesn’t respond adequately to corticosteroids or who can’t tolerate the side effects, several second-line options exist. Methotrexate and hydroxychloroquine are among the most commonly used alternatives. In cases that remain stubborn, biologic drugs that block a specific inflammatory signal called TNF-alpha, such as infliximab and adalimumab, can be effective. Infliximab in particular has shown promise for refractory pulmonary sarcoidosis and is often combined with methotrexate when used for disease involving the nervous system or eyes.