Hypersensitivity Pneumonitis

What is Hypersensitivity Pneumonitis?

Hypersensitivity pneumonitis (HP) is a type of lung disease. It happens when your lungs have a strong immune reaction due to continuously breathing in an allergen — something your body is allergic to. Although it was previously called ‘extrinsic allergic alveolitis’, the name ‘hypersensitivity pneumonitis’ describes the condition more accurately. This is because the illness doesn’t just affect the air sacs in your lungs (alveoli), but also the small air passages (bronchioles).

How severe HP is and how it appears can differ based on the allergen that’s been inhaled and how much of it was consumed. For example, the first time this illness was clinically detailed, back in 1932, the cases involved workers in Michigan and England. In Michigan, workers had been exposed to a fungus on Maple bark. In England, agricultural workers were exposed to moldy hay. Since then, many different instances from around the world that can cause HP have been documented.

In the past, doctors have divided HP into three categories — acute (quick onset), sub-acute (moderately quick onset), and chronic (long-term), based on the speed of development and the symptoms shown. However, in light of recent studies, it has been recommended that HP be classified as either Acute or Inflammatory HP (symptoms last less than six months), and Chronic or fibrotic (scarring) HP, reliant on clinical presentation, imaging, and tissue findings.

What Causes Hypersensitivity Pneumonitis?

There’s a medical condition that can occur due to an immune response triggered by certain organic substances. Over 300 of these substances have been identified and are connected with a wide variety of jobs. They can be grouped into categories such as bacteria, fungi, animal proteins, plant proteins, certain chemicals, and metals.

You might encounter these substances at work, home or in your daily life. However, it’s interesting to note that only a small portion of people who come into contact with these substances develop this condition. This suggests that it isn’t just about exposure, but it also has to do with individual genetic factors and environmental influences.

The genetic part seems to be related to variations in certain proteins known as the Major Histocompatibility Complex (MHC) Class II molecules. Another noteworthy aspect is that cigarette smoking appears to decrease the risk of developing this condition. However, if smokers do get it, their symptoms are usually more severe and they have a higher mortality risk.

The condition can be caused by exposures related to various occupations and is often named based on these occupations:

Agricultural workers, especially those who deal with livestock, can develop what’s called ‘Farmer’s lung’.

Bird or Pigeon fancier’s lung, as the name suggests, is caused by exposure to bird droppings, especially pigeon’s. But it isn’t just direct exposure; indirect exposure such as from feather bedding or down comforters can also lead to the condition.

‘Hot tub lung’ happens due to lung inflammation caused by a bacteria called Mycobacterium avium complex (MAC), and it tends to affect people who have a strong immune system.

Few other occupational exposures like ‘Cheese workers lung’, ‘Bagassosis’, ‘Mushroom workers lung’, and ‘Malt workers lung’ are also known to cause similar immune reaction.

Risk Factors and Frequency for Hypersensitivity Pneumonitis

The occurrence of hypersensitivity pneumonitis (HP), a type of lung disease, varies greatly around the world. This is due to the lack of global agreement on how to diagnose it, as well as how often people come into contact with the things that cause it (like certain types of bacteria or mold), which can change based on where and when you are. It’s also often not recognized when it’s in its early stages, because the symptoms can be very common and not seem serious. In a population record from Sweden, about 20 out of every 100,000 people each year were diagnosed with HP. Other records from Europe showed that HP made up anywhere from 1.5% to 12% of all diagnoses of interstitial lung diseases, a group of conditions that cause scarring in the lungs. Surveys looking at people with a high risk for HP found that about 1.3% to 12% of farmers and 8% to 10% of pigeon-breeders had the disease. HP that’s caused by exposure to birds is the most common type around the world. It’s reported mostly in middle-aged men and is especially common in certain jobs or hobbies where people may be exposed to the things that cause it.

HP varies greatly because there’s no global agreement on how to diagnose it, and exposure to its causes can vary.
This disease often goes unrecognized in its early stages due to non-specific symptoms.
In Sweden, about 20 out of every 100,000 people each year are diagnosed with HP.
In Europe, HP accounts for 1.5% to 12% of all diagnoses of interstitial lung diseases.
Surveys found that about 1.3% to 12% of farmers and 8% to 10% of pigeon-breeders have HP.
Bird-related HP is the most common type globally.
HP is reported most often in middle-aged men.
Certain jobs or hobbies increase the chances of exposure to the causes of HP.

Signs and Symptoms of Hypersensitivity Pneumonitis

Acute Hypersensitivity Pneumonitis (HP) is a condition where people get fever, feel unwell, cough, and have difficulty breathing within a few hours after heavy exposure to a specific antigen (a substance that triggers an immune response). These symptoms usually get better within 1 to 2 days, as long as the person avoids further exposure to the antigen. However, if a person continues to be exposed to the sensitized antigen, the symptoms can become persistent or chronic. A prominent symptom in these cases is a persistent cough due to the inflammation being centered in the airways. People with subacute and chronic HP also report feeling unwell, having shortness of breath, and losing weight.

It’s important to note that the cause of the condition may not always be found, even after a detailed history check about a person’s hobbies and work to identify any particular exposures in their environment. In fact, in up to 60% of cases, no specific trigger is identified. During a physical examination, the patient might appear normal, but there might be some abnormal sounds that can be heard in the Lungs. If the condition becomes chronic, these sounds might become more noticeable, and a condition called ‘clubbing’ (change in the shape of fingers and toes) might be observed.

Some people with chronic HP might experience a sudden worsening of their respiratory condition which can look very similar to sudden, severe worsening of a condition called Idiopathic Pulmonary Fibrosis (IPF).

Fever
Feeling unwell
A cough
Difficulty breathing
Feeling unwell
Shortness of breath
Weight loss

Testing for Hypersensitivity Pneumonitis

Diagnosing Hypersensitivity Pneumonitis (HP), a type of lung inflammation, can be challenging because it involves a combination of the patient’s detailed medical history, High-definition chest scans (HRCT), lab tests, and tissue analysis. Importantly, there isn’t a single definitive test for HP. Therefore, it’s usually necessary to have a team of professionals including lung specialists, radiologists, pathologists, and social workers, working together for an accurate diagnosis.

When it comes to lab tests, things like blood counts and other routine measurements are generally normal. However, lab markers, which are substances in the blood that can increase with inflammation such as the Erythrocyte Sedimentation Rate (ESR) and C-reactive protein (CRP) are usually elevated in people with HP.

The lab might also test patient’s blood for antibodies specific to potential triggers like molds, fungi, or grain dust. This is important in HP as identifying and then avoiding the trigger can rest the lungs and lead to improvement. However, a positive test for these antibodies only confirms exposure, not disease. Nonetheless, a negative test doesn’t entirely rule out HP either because these tests often miss cases and the specific trigger causing the patient’s HP may not be included in the test.

If the suspected trigger isn’t available for testing, they may need to gather samples from the patient’s home or workplace. Dust from these samples can then be tested to see if it contains the trigger.

In some cases, a patient might be exposed to the suspected trigger in a controlled environment to see if their symptoms worsen. This is called an Inhalational Challenge and is done in specialized centers and can provide more evidence towards a diagnosis of HP.

Further tests could include Pulmonary Function Tests, which explore lung capacity and how well your lungs work, chest X-rays or computed tomography (CT) scans. Often times, in cases of HP, chest X-rays may look normal; however, High Resolution CT scans can show more detailed changes in the lungs that are typical of HP.

More advanced cases of HP can show signs of lung fibrosis, which is the formation of scar tissue in the lung, which make it difficult to breathe. It can also cause the airways to dilate abnormally (traction bronchiectasis). A CT scan can show these changes.

Specialists might perform a procedure called a bronchoscopy where they put a flexible tube down the throat to look directly into the patient’s lungs. They can also wash a small area of the lung and then collect the fluid to look at it under a microscope, which can provide supportive evidence for the diagnosis.

If a clear diagnosis can’t be made from these tests, then obtaining a small piece of lung tissue (lung biopsy) could be considered. This might be done using the bronchoscope or during a surgical procedure. Examining lung tissue under the microscope can help make the definitive diagnosis of HP.

Treatment Options for Hypersensitivity Pneumonitis

Treatment for a certain condition often starts with finding the root cause and getting rid of it where the patient most commonly spends their time. If caught early and the trigger element or ‘antigen’ can be fully avoided, the condition can often be reversed. However, avoiding these antigens can be tough due to day-to-day activities, finances, or jobs. Protective breathing equipment might reduce certain signs of the condition, but hasn’t proven effective in preventing the more serious, chronic form. No matter the hurdles, antigen avoidance is important to stop the disease from worsening and causing unwanted scarring in the lungs.

Though there have been no specific trials for this condition, a type of medicine called glucocorticoids has been seen to speed up initial recovery. Glucocorticoids seem to be particularly beneficial for those with very severe symptoms, poor lung function tests, or significant signs on X-ray images. However, these medications don’t seem to improve outcomes in the long term and using inhaled steroids doesn’t substitute for them. Doctors typically use these medications initially and then aim to lower their use as soon as possible.

For those with chronic conditions and those whose health keeps deteriorating, doctors may suggest other treatments. Azathioprine and mycophenolate mofetil, types of medicines, have been used to reduce the use of steroids, and may help when the symptoms persist despite avoiding the antigen and taking glucocorticoids. Some other medicines have also been shown to be beneficial in small studies. The use of ‘anti-fibrotic’ medications, which help to prevent scarring, might also be suggested for cases where there’s a threat of serious lung scarring.

For those with severe advanced lung disease due to this condition, a lung transplant has shown promising survival rates. Some evidence also points that patients with this chronic condition are less prone to develop a post-transplant lung problem known as bronchiolitis obliterans syndrome.

Acute Hypersensitivity Pneumonitis (HP) may be confused with other conditions, like infections of the respiratory tract, metal fume fever, and organic dust toxic syndrome, because the symptoms are similar. To determine the true issue, doctors conduct detailed examinations as well as tests like a physical, history, and radiologic examination.

Sub-acute HP may resemble Sarcoidosis in terms of clinical appearance and radiologic picture. Key indicators of sub-acute HP include exposure history, presence of serum precipitins, and lymphocytosis on Bronchoalveolar Lavage (BAL). However, a pathological inspection in Sarcoidosis typically shows well-formed granulomas along the bronchovascular bundle, while this isn’t present in sub-acute HP. Other conditions to consider are Organizing pneumonia and smoking-related Interstitial Lung Diseases (ILD).

Chronic HP is sometimes mistaken for Usual Interstitial Pneumonia (UIP) or Idiopathic Pulmonary Fibrosis (IPF) because they share some similarities. But doctors look for indicators like:

History of exposure supporting HP
Lymphocytosis on BAL
Upper and mid zone reticulation and honeycombing in radiographic examination
Patchy areas of ground-glass opacities and air trapping
Fibrosis predominantly involving the upper zone and peri-bronchiolar areas
Presence of granulomas and lymphocytic interstitial inflammation

While UIP typically has marked sub-pleural fibrosis and microscopic honeycombing.

Fibrotic Non-Specific Interstitial Pneumonia (NSIP) can also seem similar to chronic HP in terms of radiographic and pathological appearance, with granulomas and giant cells indicating chronic HP. Overlap syndromes for HP and NSIP have been reported.

What to expect with Hypersensitivity Pneumonitis

Identifying the problem early and completely avoiding what’s causing the problem can lead to a full recovery of lung function for most patients. However, if fibrosis, or scarring, occurs in the lungs, this generally means a poor outlook with an average life expectancy of 3 to 5 years. Other factors that can lead to worse outcomes include older age, high exposure to whatever is causing the problem, a delayed diagnosis, smoking, absence of high levels of white blood cells in the fluid from the lungs, recurring severe flare-ups, and high blood pressure in the lungs.

Possible Complications When Diagnosed with Hypersensitivity Pneumonitis

If not diagnosed and treated immediately as previously mentioned, Hypersensitivity Pneumonitis (HP) can worsen into pulmonary fibrosis and gradually lead to respiratory failure. Pulmonary fibrosis and honeycombing, a lung disease that looks like beehive under a CT scan, are often associated with higher chances of death.

Prevention is best achieved by limiting the exposure of agricultural workers to certain known organic antigens and providing safety training. This would involve improving engineering methods, proper maintenance, utilization of personal protective gear, and health and safety education. Detecting a case of HP at the workplace should lead to a thorough examination of the workspace, and a review of other workers’ health in order to identify and address any extra cases early.

Common Preventative Measures:

Reducing exposure to certain organic antigens
Providing safety and health education
Implementing better engineering techniques
Ensuring regular maintenance of equipment
Encouraging use of personal protective equipment
Conducting a detailed review of the workplace if HP case is detected
Surveying other workers to diagnose additional cases early

Frequently asked questions

Hypersensitivity pneumonitis is a type of lung disease that occurs when the lungs have a strong immune reaction to breathing in an allergen that the body is allergic to. It affects both the air sacs in the lungs and the small air passages.

In Sweden, about 20 out of every 100,000 people each year are diagnosed with HP.

The signs and symptoms of Hypersensitivity Pneumonitis include: - Fever - Feeling unwell - A cough - Difficulty breathing - Shortness of breath - Weight loss These symptoms typically occur within a few hours after heavy exposure to a specific antigen. In some cases, the symptoms may improve within 1 to 2 days if further exposure to the antigen is avoided. However, if a person continues to be exposed to the sensitized antigen, the symptoms can become persistent or chronic. In chronic cases, a persistent cough is a prominent symptom due to inflammation in the airways. People with subacute and chronic HP also report feeling unwell, experiencing shortness of breath, and losing weight. It's important to note that in up to 60% of cases, no specific trigger for the condition is identified. During a physical examination, the patient may appear normal, but abnormal sounds may be heard in the lungs. If the condition becomes chronic, these sounds may become more noticeable, and a condition called 'clubbing' (change in the shape of fingers and toes) may be observed.

Hypersensitivity Pneumonitis can be caused by exposure to certain organic substances, such as bacteria, fungi, animal proteins, plant proteins, certain chemicals, and metals. It can occur due to occupational exposures in various jobs or hobbies, such as agricultural work, bird or pigeon handling, cheese making, and mushroom or malt processing.

The doctor needs to rule out the following conditions when diagnosing Hypersensitivity Pneumonitis: 1. Infections of the respiratory tract 2. Metal fume fever 3. Organic dust toxic syndrome 4. Sarcoidosis 5. Organizing pneumonia 6. Smoking-related Interstitial Lung Diseases (ILD) 7. Usual Interstitial Pneumonia (UIP) 8. Idiopathic Pulmonary Fibrosis (IPF) 9. Fibrotic Non-Specific Interstitial Pneumonia (NSIP)

The types of tests needed for Hypersensitivity Pneumonitis include: - High-definition chest scans (HRCT) - Lab tests, including blood counts and lab markers such as Erythrocyte Sedimentation Rate (ESR) and C-reactive protein (CRP) - Blood tests for antibodies specific to potential triggers like molds, fungi, or grain dust - Testing of samples from the patient's home or workplace for triggers - Inhalational Challenge to see if symptoms worsen in a controlled environment - Pulmonary Function Tests to explore lung capacity and function - Chest X-rays or computed tomography (CT) scans, with CT scans being more detailed - Bronchoscopy to directly examine the lungs and collect fluid for analysis - Lung biopsy to examine lung tissue under a microscope for a definitive diagnosis.

Hypersensitivity Pneumonitis can be treated through a combination of approaches. The initial step is to identify and eliminate the root cause or antigen that triggers the condition. If caught early and the antigen can be fully avoided, the condition can often be reversed. Protective breathing equipment may help reduce certain symptoms, but it is not effective in preventing the more serious, chronic form of the disease. Glucocorticoids, a type of medicine, can speed up initial recovery, particularly for those with severe symptoms or poor lung function. Other medications like azathioprine and mycophenolate mofetil may be used to reduce the use of steroids. In cases of severe advanced lung disease, a lung transplant has shown promising survival rates.

There are several side effects when treating Hypersensitivity Pneumonitis, including: - Antigen avoidance can be challenging due to day-to-day activities, finances, or jobs. - Protective breathing equipment may reduce certain signs of the condition but has not proven effective in preventing the more serious, chronic form. - Glucocorticoids, a type of medicine, can speed up initial recovery but do not improve outcomes in the long term. - Azathioprine and mycophenolate mofetil, other types of medicines, may be used to reduce the use of steroids when symptoms persist despite antigen avoidance and glucocorticoid use. - 'Anti-fibrotic' medications may be suggested to prevent scarring in cases where there is a threat of serious lung scarring. - In severe advanced cases, a lung transplant has shown promising survival rates.

The prognosis for Hypersensitivity Pneumonitis depends on several factors, including the stage of the disease and the presence of complications such as fibrosis. If the problem is identified early and the patient completely avoids the allergen causing the reaction, there is a chance for full recovery of lung function. However, if fibrosis occurs, the outlook is generally poor with an average life expectancy of 3 to 5 years. Other factors that can lead to worse outcomes include older age, high exposure to the allergen, delayed diagnosis, smoking, recurring severe flare-ups, and high blood pressure in the lungs.

A team of professionals including lung specialists, radiologists, pathologists, and social workers should be consulted for an accurate diagnosis of Hypersensitivity Pneumonitis.