Hypersensitivity Pneumonitis Imaging

Introduction:

Lungs are the crucial organs of the respiratory system that supply oxygen to the cells and tissues in the body. Diseases affecting the respiratory system may hinder the oxygen supply throughout the body resulting in grave complications. Infections and inflammation are the most common disorders affecting the respiratory organs. Quick diagnosis and prompt treatment are crucial to prevent fatalities and, thereby, better prognosis.

What Is Pneumonitis?

Inflammation of the lung is known as pneumonitis. Pneumonia is a type of pneumonitis but of infective origin. In contrast, pneumonitis is non-infective in origin, more like an allergic reaction. The most common cause of pneumonitis is respiratory tract irritation by airborne substances. Though pneumonitis is entirely treatable, a delayed diagnosis could result in scar tissue formation in the lungs and long-term permanent damage.

What Is Hypersensitivity Pneumonitis?

Hypersensitivity pneumonitis is lung inflammation caused by exposure to an allergen such as dust, fungus, bird feathers, animal or rodent droppings, or household molds. It is not a contagious disease. The inflammation of lung tissue causes difficulty in breathing, resulting in acute lung diseases. Progressive exposure would result in chronic disease with irreversible scarring of lung tissue and severe lung damage.

What Are the Risk Factors Associated With Hypersensitivity Pneumonitis?

Hypersensitivity pneumonitis most commonly affects people working in places with an increased probability of exposure to allergens. The people most affected include:

• Farmers working with dairy cattle, grain, or vegetables. This type is known as a farmer's lung, caused by repeated exposure to mold, hay, and straw dust from the farms.

• Workers in chemical industries, particularly those associated with isocyanates or acid anhydrides.

• Veterinarians and bird or poultry handlers.

• Workers who process and load grains and flour.

• Workers in lumber (timber) mills.

• Paint industry workers.

• Paper manufacturers.

• People who keep pet birds, as bird dropping and feathers are potent allergens. This type of hypersensitivity pneumonitis is also known as bird fancier's lung.

• Breathing from uncleansed humidifiers, heating systems, or air conditioners can also result in a type of hypersensitivity pneumonitis known as humidifier lung.

• Hot tub lung is a type of hypersensitivity pneumonitis caused by inhaling the bacteria from hot tub water vapor.

What Causes Hypersensitivity Pneumonitis?

There are over 300 known allergens responsible for hypersensitivity pneumonitis. They include molds, fungi, bacteria, chemicals, and certain proteins. Acute hypersensitivity pneumonitis usually occurs within four to six hours of inhaling the allergen. They can generally be treated successfully. However, chronic cases occur when individuals are exposed to low levels of allergen for an extended period. It may take months or years for the patients to develop symptoms.

What Are the Symptoms of Hypersensitivity Pneumonitis?

The symptoms vary depending on whether the condition is acute or chronic. The symptoms of acute hypersensitivity pneumonitis are:

• Difficulty in breathing.

• Dry cough.

• Chills.

• Fever.

• Tiredness.

• Tightness around the chest.

Chronic hypersensitivity pneumonitis may have the following symptoms:

• Persistent cough.

• Weight loss.

• Fatigue.

• Shortness of breath, particularly with activity or physical exertion.

• Progressive cases may lead to pulmonary fibrosis.

Symptoms of pulmonary fibrosis may be as mentioned below:

• Fast, shallow breathing.

• Dry cough.

• Weight loss.

• Shortness of breath.

• Fatigue.

• Clubbing (round and widened) of the finger and toe.

What Are the Complications of Hypersensitivity Pneumonitis?

Chronic cases of hypersensitivity pneumonitis may result in pulmonary fibrosis, which is scarring of the lung tissues. It would lead to severe breathing issues and deprives body tissues of oxygen. Individuals with chronic hypersensitivity issues are more prone to develop pulmonary hypertension, which may eventually lead to permanent and irreversible lung damage. However, early diagnosis and thorough treatment can prevent long-term complications, and the condition can be easily reversed.

How to Diagnose Hypersensitivity Pneumonitis?

The diagnostic workup of hypersensitivity pneumonitis is as given below:

• Physical Examination and Medical History- A detailed medical history and a complete physical examination will be sufficient enough to provide a provisional diagnosis. The medical history may include a history of allergy, allergen exposure, occupational history, and also exposure to pet droppings or bird feathers. Physical examination may involve auscultating the lungs for abnormal sounds. A pulse oximeter may be used to assess the oxygen level.

• Radiography- Chest X-ray is the quickest and most conveniently accessible diagnostic aid, particularly for chest abnormalities. It is non-invasive, and the results can be interpreted immediately. Since X-ray is portable, they could be universally used. It is highly beneficial to detect early changes in the lungs. It can also be used to differentiate hypersensitivity pneumonitis from other respiratory diseases. The acute and subacute phases are identified in the X-ray as small (one to five millimeters in size) bilateral pulmonary nodules. Unilateral is rarely found. The periphery of the nodule may be distinct or ill-defined. These nodules are usually found in the middle of the lower lobe of the lungs. Hilar lymphadenopathy may also be occasionally observed. Chronic disease may be marked by extensive fibrosis and loss of lung volume with lace-like opacities. Though it is the most convenient tool, certain features may be non-specific. A confirmatory diagnosis cannot be made entirely based on the chest X-ray. Hence correlating the radiographic findings with clinical symptoms and medical history is essential for a conclusive diagnosis. Also, its limitations include pregnant women and young adults, where the possibility of radiation exposure cannot be excluded.

• Computed Tomography (CT)- High-resolution CT (HRCT) is most commonly preferred to diagnose and stage the disease. In acute conditions, the CT findings may be normal or show ground-glass nodular opacities. The subacute phase may show ground-glass opacities, poorly defined nodules, and areas of air trapping. The sensitivity and specificity of HRCT are higher than conventional X-rays in diagnosing hypersensitivity pneumonitis.

• Lung Function Tests- Lung function tests can determine if the lungs are working efficiently. They can also detect any breathing abnormalities if present.

• Blood Tests- Blood tests can be done to identify the allergen.

• Bronchoscopy- Bronchoscopy is an invasive test that provides a detailed image of the lungs and the air sacs. A bronchoscope is a thin, flexible tube with a camera attached to its end. The bronchoscope is inserted through the nose into the lungs. This procedure enables easy visualization of the damage to the lung tissue, such as scarring and fibrosis.

• Lung Biopsy- Although rarely performed, video-assisted thoracic surgery or an open lung biopsy may be done in unresponsive cases.

Conclusion:

Hypersensitivity pneumonitis can be treated effectively by simply avoiding the allergen. The symptoms are self-resolving if diagnosed earlier. However, chronic or progressive cases need effective treatment. A delay in diagnosis or management may result in end-stage lung disease and respiratory failure.