What is HP?

What is hypersensitivity pneumonitis?

Hypersensitivity pneumonitis (HP) is an immune-mediated lung disease caused by inhaling many different foreign substances called antigens.  These foreign materials can prompt an immune reaction in the small airways and air sacs of the lungs, which may lead to acute lung disease. Over time and with continued exposure to the substance, chronic lung disease with permanent scarring may occur.  Hypersensitivity peumonitis is not an allergy nor a genetic tendency to develop an allergic disease. It is one a 200 types if interstitial lung disease.

Causes

Hypersensitivity pneumonitis can develop from inhaled antigens such as:

• Animal proteins
• Bacteria
• Chemicals
• Dust from air conditioners, humidifiers and ventilation systems
• Fungi
• Microorganisms
• Plant matter

The illness varies in severity and is categorized as fibrotic (lung scarring) or nonfibrotic (without lung scarring).

Signs and Symptoms

Hypersensitivity pneumonitis symptoms can develop quickly or slowly and may worsen over months or years. Symptoms may suddenly become more acute from time to time.. Chronic symptoms may develop after many or continuous exposures to antigens.

Symptoms of Fibrotic Hypersensitivity Pneumonitis

• Chills
• Chest tightness
• Dry cough
• Fatigue
• Fever
• Muscle aches
• Shortness of breath

Symptoms of Nonfibrotic Hypersensitivity Pneumonitis

• Abnormal sounds when you breathe
• Cough
• Fatigue
• Finger or toe clubbing (thickening of flesh under the fingernails)
• Flu-like illness
• Shortness of breath that worsens with exertion
• Weight loss

Risks

Age: Hypersensitivity pneumonitis can develop at any age, but many patients are diagnosed between 50 and 70 years old.

Family history: Certain abnormal genes may raise the risk of developing hypersensitivity pneumonitis or increase the likelihood of developing HP with lung fibrosis. Additionally, if a family member has HP or another interstitial lung disease (ILD), your chances of developing hypersensitivity pneumonitis may be higher.

Infections: Some viral and bacterial infections may increase the risk of worsening HP, particularly in older adults.

Occupation: People who work in certain occupations may be at a higher risk of developing hypersensitivity pneumonitis. These jobs include:

• Animal handlers
• Bird breeders
• Chemical plant employees
• Farmers
• Grain and flour processors
• Poultry handlers
• Veterinary workers
• Woodworkers

Diagnosis

Your doctor will conduct a thorough physical examination and medical history and ask about your symptoms to diagnose hypersensitivity pneumonitis. They may ask questions about your work or living environment to determine if you could have been exposed to certain antigens. Your doctor also may conduct a variety of tests.

Breathing and Exercise Tests

Lung function tests: These breathing tests measure how your lungs and airways function and enable physicians to make diagnoses, recommend ILD treatment and track progress.

Imaging Tests

Chest x-ray: A chest X-ray is a picture of the inside of the chest, used to evaluate the lungs, heart, and other structures of the chest.

HRCT scan: A high-resolution computed tomography (HRCT) scan takes a 3-d image of your lungs.

Lab Tests

Antigen blood tests (hypersensitivity pneumonitis panel): These blood tests check for antibodies to an antigen. Complete blood count: A complete blood count (CBC) is a blood test that counts your red blood cells, hemoglobin, white blood cells and platelets.

Procedures

Bronchoscopy: This test involves inserting a tube through the nose or mouth into the trachea (windpipe) so the doctor can see the airways, check for inflammatory cells in the lungs or sample small pieces of the lung to look for evidence of hypersensitivity pneumonitis.

Surgical lung biopsy: For a specific diagnosis of hypersensitivity pneumonitis, a surgical lung biopsy is necessary to extract enough lung tissue to analyze. This may be performed with a thoracoscope to allow the surgeon to biopsy multiple areas of one lung with few very small incisions.

Treatment

Hypersensitivity pneumonitis without lung scaring (nonfibrotic) may go away within a few days if you avoid exposure to the antigen. Your symptoms may improve significantly if you are no longer exposed to the antigen.

Hypersensitivity pneumonitis with lung scarring (fibrotic) usually doesn’t go away, but medication and other treatments can make your symptoms more manageable. It may take several months for your lungs to heal from HP-related inflammation. It's important to adhere to your treatment plan and see your doctor for regular follow-ups. HP can be fatal without a lung transplant for patients with lung scarring.

Avoid Triggers of Hypersensitivity Pneumonitis

Identifying and avoiding the antigen trigger of your HP is key for treatment. Hypersensitivity pneumonitis won’t go away completely if you are still exposed to the antigen, even with medication.

Medications

Anti-fibrotic drugs: Medications such as pirfenidone and nintedanib can slow lung scarring.

Corticosteroids or other immunosuppressive medications: These treatments reduce inflammation in the lungs and prevent your immune system from reacting to inhaled allergens. You may need to take this medication for several months depending on the severity of your hypersensitivity pneumonitis.

Therapies

Oxygen therapy: Low levels of oxygen in the blood can be treated with supplemental oxygen.

Pulmonary rehabilitation: Breathing exercises and physical therapy can help you breathe easier and improve your quality of life.

Procedures

Lung transplant: If you have advanced lung scarring that hasn’t responded to other treatments, your doctor may recommend a lung transplant.

Clinical Trials

Clinical trials are research studies that test new medical treatments, procedures, or devices to determine their safety and effectiveness. They help many patients who have not responded well to standard treatments. Patients interested in participating in a clinical trial should talk with their doctor to understand which trials may be right for them.