Summary about Disease
Hypersensitivity pneumonitis (HP), also known as extrinsic allergic alveolitis, is an inflammatory lung disease caused by an exaggerated immune response to inhaled organic dusts, molds, fungi, bacteria, animal proteins, or chemicals. Repeated exposure to these substances triggers inflammation in the small air sacs (alveoli) and bronchioles of the lungs, leading to a variety of respiratory symptoms. HP can present in acute, subacute, or chronic forms, depending on the frequency and intensity of exposure and individual susceptibility.
Symptoms
Symptoms vary depending on the form of HP (acute, subacute, or chronic).
Acute: Sudden onset of cough, shortness of breath, fever, chills, muscle aches, and fatigue, typically occurring 4-8 hours after exposure to the offending antigen.
Subacute: Gradual onset of cough, shortness of breath, fatigue, weight loss, and a general feeling of being unwell.
Chronic: Progressive shortness of breath, cough, fatigue, weight loss, and clubbing of the fingers (widening and rounding of the fingertips). Eventually, chronic HP can lead to irreversible lung damage (pulmonary fibrosis).
Causes
HP is caused by inhaling specific allergens that trigger an immune response in the lungs. Common causes include:
Mold/Fungi: Found in hay, grain, compost, humidifiers, air conditioners, and other damp environments (e.g., "Farmer's Lung," "Humidifier Lung").
Bacteria: Found in contaminated water systems or in certain industrial processes.
Animal Proteins: Bird droppings (e.g., "Bird Fancier's Lung"), animal dander, laboratory animals.
Chemicals: Isocyanates (used in paints, varnishes, and insulation), certain medications.
Other Organic Dusts: Found in mushroom farming, cheese production, or other agricultural settings.
Medicine Used
Treatment focuses on reducing inflammation and managing symptoms.
Corticosteroids: Prednisone is commonly used to reduce inflammation in the lungs, especially in acute and subacute cases.
Immunosuppressants: In severe or chronic cases, other immunosuppressant medications like azathioprine or mycophenolate mofetil may be used.
Oxygen Therapy: Supplemental oxygen may be needed to help with breathing, especially in advanced cases.
Pulmonary Rehabilitation: Helps improve lung function and quality of life.
Bronchodilators: May be used to open up airways and ease breathing, though less commonly than in other lung diseases.
Is Communicable
No, hypersensitivity pneumonitis is not contagious. It is caused by an individual's immune response to inhaled substances and cannot be transmitted from person to person.
Precautions
The most important precaution is to identify and avoid the offending antigen.
Environmental Control: Thoroughly clean and disinfect areas where mold or other allergens are present. Remove or replace contaminated materials. Improve ventilation.
Protective Equipment: Use masks (e.g., N95 respirators) when exposure to known allergens is unavoidable.
Medical Management: Regularly monitor lung function and follow your doctor's recommendations.
Smoking Cessation: If you smoke, quitting is crucial for overall lung health.
How long does an outbreak last?
Acute HP: Symptoms usually resolve within a few days to weeks after exposure ceases.
Subacute HP: Symptoms can persist for weeks to months.
Chronic HP: Symptoms can be ongoing and progressive, leading to permanent lung damage over months to years if exposure continues.
How is it diagnosed?
Diagnosis involves a combination of factors:
Medical History: Detailed information about exposure history, symptoms, and other medical conditions.
Physical Examination: Listening to the lungs with a stethoscope.
Pulmonary Function Tests (PFTs): Measures lung capacity and airflow.
Chest X-ray or CT Scan: To visualize lung inflammation and scarring.
Bronchoalveolar Lavage (BAL): Fluid is collected from the lungs and examined for inflammatory cells.
Lung Biopsy: In some cases, a small tissue sample from the lung is needed for examination.
Specific IgE or IgG Antibody Tests: Blood tests that can identify antibodies to specific allergens, but are not always definitive.
Provocation Testing: Involves carefully exposing the person to a suspected antigen to observe for a reaction (rarely done).
Timeline of Symptoms
Acute HP: Within 4-8 hours of exposure: cough, shortness of breath, fever, chills, muscle aches, fatigue. Symptoms subside within days to weeks if exposure stops.
Subacute HP: Gradual onset over weeks to months: cough, shortness of breath, fatigue, weight loss.
Chronic HP: Insidious onset and progression over months to years: progressive shortness of breath, cough, fatigue, weight loss, clubbing of fingers.
Important Considerations
Early Diagnosis: Early diagnosis and removal of the offending antigen are crucial to prevent irreversible lung damage.
Individual Variability: Not everyone exposed to the same allergen will develop HP. Genetic predisposition and other factors play a role.
Long-Term Monitoring: Patients with HP need long-term monitoring of their lung function to detect any progression of disease.
Differential Diagnosis: HP can mimic other lung diseases, so it is important to rule out other conditions like asthma, COPD, and infections.
Multidisciplinary Approach: Management often requires a team of specialists, including pulmonologists, allergists/immunologists, and occupational health physicians.