What causes pneumonitis

Overview

Pneumonitis, also known as pneumonitis, is a general term for inflammation of the lung tissue. This inflammation can affect the air sacs (alveoli) and the spaces between them within the lungs. When the alveoli are inflamed, they can fill with fluid or pus, making it difficult for oxygen to pass into the bloodstream, leading to symptoms like shortness of breath.

Causes of Pneumonitis

The causes of pneumonitis are diverse and can be broadly categorized into several groups:

Infections

One of the most common causes of pneumonitis is infection. This can be due to:

• Bacteria: Bacterial pneumonia is a well-known type of pneumonitis caused by various bacteria, such as Streptococcus pneumoniae, Haemophilus influenzae, and Mycoplasma pneumoniae.
• Viruses: Viral infections like influenza (flu), respiratory syncytial virus (RSV), adenovirus, and coronaviruses (including SARS-CoV-2, the virus that causes COVID-19) can lead to viral pneumonitis.
• Fungi: Fungal infections, particularly in individuals with weakened immune systems, can cause fungal pneumonitis. Examples include Pneumocystis jirovecii pneumonia (PJP), often seen in people with HIV/AIDS, and infections from molds like Aspergillus.
• Parasites: Though less common in many parts of the world, parasitic infections can also cause pneumonitis.

Inhaled Irritants

Exposure to certain substances in the air can trigger an inflammatory response in the lungs:

• Environmental factors: Inhaling dust (e.g., from construction, agriculture, or bird droppings), mold spores, animal dander, or fumes from chemicals, cleaning products, or industrial processes can lead to pneumonitis. This is often referred to as hypersensitivity pneumonitis when the immune system overreacts to inhaled organic dusts.
• Occupational exposures: Workers in certain industries, such as farming, textile manufacturing, and woodworking, are at higher risk due to prolonged exposure to specific airborne irritants.

Medications

A variety of drugs can cause pneumonitis as a side effect. This is often an immune-mediated reaction to the medication. Common culprits include:

• Chemotherapy drugs: Many cancer treatments can damage lung tissue.
• Heart medications: Such as amiodarone.
• Antibiotics: Certain types of antibiotics.
• Anti-inflammatory drugs: Including biologics used to treat autoimmune conditions.
• Illegal drugs: Such as cocaine.

The reaction can occur days, weeks, or even months after starting a new medication.

Autoimmune Diseases

In individuals with autoimmune conditions, the body's immune system mistakenly attacks its own healthy tissues, including the lungs. This can lead to inflammation and scarring of the lung tissue. Examples of autoimmune diseases that can cause pneumonitis include:

• Rheumatoid arthritis
• Lupus (Systemic Lupus Erythematosus)
• Scleroderma (Systemic Sclerosis)
• Polymyositis and Dermatomyositis
• Sjögren's syndrome

Aspiration

When foreign material, such as stomach contents, food, or liquids, is inhaled into the lungs, it can cause irritation and inflammation, leading to aspiration pneumonitis. This is more common in individuals with conditions that affect swallowing, such as stroke or neurological disorders.

Other Causes

Less common causes include radiation therapy to the chest area, certain lung diseases like sarcoidosis, and idiopathic interstitial pneumonias, where the cause is unknown.

Symptoms and Diagnosis

Symptoms of pneumonitis can vary depending on the cause and severity but commonly include:

• Shortness of breath (dyspnea), which may worsen with activity
• Dry cough
• Fever and chills
• Fatigue and weakness
• Chest pain
• Muscle aches
• Weight loss

Diagnosis typically involves a thorough medical history, physical examination, imaging tests (chest X-ray, CT scan), pulmonary function tests to assess lung capacity, and sometimes blood tests or a lung biopsy to identify the specific cause.

Treatment

Treatment for pneumonitis is directed at the underlying cause. This may include antibiotics for bacterial infections, antiviral medications for viral infections, corticosteroids to reduce inflammation, or immunosuppressants for autoimmune causes. Avoiding exposure to inhaled irritants is crucial for hypersensitivity pneumonitis. In severe cases, supportive care such as oxygen therapy or mechanical ventilation may be necessary.