Alveolitis, also known as interstitial alveolitis or alveolar inflammation, refers to inflammation of the alveoli, the tiny air sacs in the lungs where oxygen and carbon dioxide are exchanged. This inflammation can disrupt normal lung function and lead to symptoms like cough, shortness of breath, and chest discomfort. The causes of alveolitis are diverse and often complex, involving a range of environmental, infectious, autoimmune, and other factors.
One major cause of alveolitis is **autoimmune diseases**. Conditions such as rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis, polymyositis, dermatomyositis, and Sjögren’s syndrome can trigger an immune response that mistakenly attacks lung tissue, including the alveoli. This immune-mediated attack leads to inflammation and sometimes scarring of the lung tissue. In these diseases, immune cells infiltrate the alveolar walls, causing swelling and damage that impair gas exchange. For example, in Sjögren’s syndrome, lymphocytic infiltration of lung tissue can cause alveolitis, leading to symptoms like cough and difficulty breathing.
Another significant cause is **inhalation of harmful substances**. Breathing in inorganic dusts such as silica (silicosis), asbestos (asbestosis), or beryllium can provoke an inflammatory reaction in the alveoli. Organic dusts, molds, fungi, and other allergens can cause hypersensitivity pneumonitis, also called extrinsic allergic alveolitis. This is an immune system reaction to inhaled organic particles, leading to inflammation in the alveoli and surrounding lung tissue. Continuous or repeated exposure to these inhaled irritants can cause chronic alveolitis and eventually fibrosis, which is scarring that stiffens the lungs.
**Infections** are another common cause of alveolitis. Viral infections like COVID-19, respiratory syncytial virus, and atypical pneumonia can inflame the alveoli. Bacterial infections such as tuberculosis or infections caused by organisms like Chlamydia trachomatis and Pneumocystis jirovecii (which causes Pneumocystis pneumonia) can also lead to alveolar inflammation. Infections provoke an immune response that brings inflammatory cells to the alveoli, causing swelling and fluid accumulation that interfere with oxygen exchange.
Certain **medications and treatments** can induce alveolitis as a side effect. Drugs such as some antibiotics (nitrofurantoin, sulfa drugs), chemotherapeutic agents, antiarrhythmic drugs, and radiation therapy can damage lung tissue, triggering inflammation. This drug-induced alveolitis occurs because these substances can be toxic to lung cells or provoke an immune reaction that inflames the alveoli.
**Smoking** is a well-known risk factor that can cause or worsen alveolitis. Smoking introduces numerous harmful chemicals and particles into the lungs, which can cause chronic inflammation and damage to alveolar tissue. Smoking-related interstitial fibrosis is a form of lung disease linked to smoking that involves alveolar inflammation and scarring.
In some cases, alveolitis occurs without a clearly identifiable cause, known as idiopathic alveolitis or idiopathic pulmonary fibrosis when scarring is involved. This condition involves progressive inflammation and fibrosis of the alveoli and surrounding lung tissue, leading to stiff lungs and impaired breathing.
The process of alveolitis typically begins when the alveolar walls become inflamed due to the immune system’s response to injury or irritation. This inflammation increases the number of immune cells, such as lymphocytes and macrophages, in the alveolar spaces and interstitium (the tissue around the alveoli). The alveolar walls may thicken, and fluid can accumulate, reducing the lungs’ ability to transfer oxygen into the blood. Ove
