Pneumonitis is a respiratory condition defined by inflammation occurring in the lung tissue. This inflammation primarily affects the tiny air sacs, called alveoli, and the surrounding structures, which collectively make up the gas-exchange surfaces of the lungs. When these tissues become swollen and irritated, it can significantly interfere with the body’s ability to transfer oxygen into the bloodstream. The term pneumonitis is used broadly to describe this inflammation, regardless of its underlying cause.
Defining Pneumonitis and How It Differs from Pneumonia
Pneumonitis is frequently confused with pneumonia, but a fundamental distinction exists in their causes. Pneumonitis refers to inflammation of the lung tissue that is not caused by an infection. This non-infectious inflammation is often triggered by an immune reaction to an inhaled substance, a medication, or radiation exposure.
Pneumonia, conversely, is a specific type of lung inflammation directly caused by an infection from microorganisms. The inflammation in pneumonia is typically a response to bacteria, viruses, or fungi that have invaded the lung tissue. This infectious process often leads to the accumulation of fluid and pus inside the air sacs.
While both conditions involve inflamed lung tissue, the origin of the inflammation is what sets them apart. Pneumonitis involves a sterile, non-infectious inflammatory response, while pneumonia is characterized by an active infection. Understanding this difference is important because the treatment approach for each condition is completely different. Using antibiotics for non-infectious pneumonitis is ineffective.
Triggers of Lung Inflammation
The causes of pneumonitis are diverse and are typically grouped by the type of non-infectious agent responsible.
Hypersensitivity Pneumonitis
This condition, also known as Extrinsic Allergic Alveolitis, occurs when the immune system reacts strongly to repeated inhalation of organic dusts. Common environmental triggers include mold spores found in poorly maintained humidifiers, air conditioners, or hot tubs (“hot tub lung”). Professional exposures are also frequent causes, such as inhaling moldy hay or grain dust (“farmer’s lung”), or exposure to bird droppings or feathers (“bird-fancier’s lung”). Hypersensitivity pneumonitis can manifest acutely with flu-like symptoms or chronically, leading to gradual lung changes.
Drug-Induced Pneumonitis
Certain medications trigger an inflammatory response in the lung tissue. A wide range of drugs has been implicated, including some chemotherapy agents, certain antibiotics, and heart rhythm medications. The drugs may either directly irritate the lung cells or cause a strong immune system reaction.
Radiation Pneumonitis
This is a specific complication that arises after a patient receives radiation therapy, most often for lung or breast cancer. The radiation damages the lung tissue, leading to an inflammatory process that typically appears one to three months following the completion of the treatment.
Chemical Pneumonitis
This occurs after inhaling highly toxic fumes or aspirating acidic stomach contents. This causes a direct chemical burn and severe inflammation in the airways.
Symptoms and Diagnostic Methods
The symptoms of pneumonitis can vary widely, often depending on whether the condition is acute or chronic. In acute cases, symptoms may appear hours after a significant exposure and can resemble the flu, including fever, chills, and a dry cough. The most common complaint across all forms is shortness of breath, often accompanied by fatigue.
Chronic pneumonitis results from long-term, low-level exposure and presents more subtly with a persistent cough, increasing difficulty breathing, and unintended weight loss. A physician will first take a detailed medical and exposure history to identify potential irritants before performing a physical exam, which may reveal abnormal crackling sounds in the lungs.
Diagnostic testing is essential to confirm the inflammation and rule out an infection. Imaging tests, such as Chest X-rays and High-Resolution Computed Tomography (HRCT) scans, are used to visualize changes in the lung tissue. HRCT is particularly useful for detecting interstitial changes, like ground-glass opacities or signs of developing fibrosis.
Pulmonary Function Tests (PFTs) measure lung capacity and air flow, often showing a restrictive pattern that confirms the decreased ability of the lungs to hold air. To further refine the diagnosis, a procedure called Bronchoalveolar Lavage (BAL) may be performed. Analyzing the collected fluid for specific inflammatory cells, such as an elevated lymphocyte count, can help pinpoint the cause and distinguish pneumonitis from other lung diseases.
Treating Pneumonitis
The most important step in managing pneumonitis is the immediate and complete removal of the offending agent or trigger. For hypersensitivity pneumonitis, this may involve environmental changes, such as eliminating mold sources or avoiding exposure to birds. If the cause is a medication, the drug must be safely discontinued under medical supervision.
If the disease is caught early, simple avoidance of the trigger can often lead to a full reversal of the lung damage. In more severe cases, medical management is necessary to reduce the inflammatory response. Corticosteroids, such as prednisone, are the primary anti-inflammatory medications used to suppress the immune reaction and prevent permanent scarring.
The typical course involves a high dose of oral steroids initially, followed by a gradual reduction over several weeks or months. While corticosteroids are effective for acute and non-fibrotic pneumonitis, their impact is less pronounced once irreversible scarring, known as pulmonary fibrosis, has occurred. If chronic inflammation leads to significant fibrosis, the damage is generally permanent, potentially requiring long-term oxygen therapy.