Hypersensitivity Pneumonitis: Understanding and Recovery

October 27, 2024

Hypersensitivity pneumonitis, previously known as Allergic alveolitis, is an inflammatory lung disorder caused by the immune system responding excessively to harmless particles in the air. When it starts to happen, the body launches an excessive attack to fight off the perceived infection. This is when it ends up damaging the lungs.

What is Hypersensitivity Pneumonitis?

Hypersensitivity Pneumonitis¹ is an immune system disorder triggered by inhaled particles like dust or fungi. The body’s overreaction to these allergens leads to fragile lung alveoli becoming inflamed, resulting in breathing difficulty and even pneumonia. It is a type of interstitial lung disease (ILD) characterized by inflammation of the lung tissue. Symptoms include shortness of breath, cough, fatigue, chest discomfort, weight loss, and sometimes finger clubbing. Prompt diagnosis and treatment are important to prevent further lung damage. It is essential to remember that any outside agent does not cause this sickness; instead, it comes from an overactive immune system.
Interestingly enough, some familiar names for Hypersensitivity Pneumonitis include “bird fancier’s lung” due to exposure from bird droppings and feathers; “humidifier lung,” which is caused by continuous moisture exposure; and lastly, “farmer’s lung,” commonly found within farmers who inhale various organic particles during their workdays.

Implications of Hypersensitivity Pneumonitis

Hypersensitivity Pneumonitis Causes

Hypersensitivity Pneumonitis is caused by repetitive inhalation of antigens (a foreign substance that stimulates the immune system) from the environment. Common antigens include dust particles, molds, bacteria, fungi, bird droppings, chemicals, animal proteins, and agricultural dust.
Farmers and breeders working in the agriculture and animal husbandry domain are at risk of developing it due to their continuous exposure to antigens.

Types of Hypersensitivity Pneumonitis

It has three main types: Acute, Subacute, and chronic.

Acute Hypersensitivity Pneumonitis (HP) lasts hours to days and manifests as fever, chills, cough, and headache.
Subacute HP is between acute and chronic HP. This type lasts days to weeks and manifests as cough, shortness of breath, and fatigue.
The chronic form of HP lasts longer (months to years) and is due to continuous exposure to antigens. Its main manifestations are weight loss, tiredness, and persistent cough.

It can also be divided into fibrotic and non-fibrotic types.

In non-fibrotic HP, inflammation occurs within the lung tissue without significant fibrotic changes. This means that inflammation is the primary pathological feature, and no significant scarring or fibrosis is observed.

In contrast, fibrotic HP is characterized by the presence of both inflammation and fibrosis. Fibrosis refers to the formation of excess scar tissue in the lungs, which can lead to progressive stiffening and impairment of lung function over time.

It’s important to note that the presence or absence of fibrosis can have implications for the prognosis and management of HP, as fibrotic HP tends to have a worse long-term outcome compared to non-fibrotic HP.

Signs & Symptoms of Hypersensitivity Pneumonitis

The signs and symptoms of hypersensitivity pneumonitis² differ in acute and chronic conditions. Acute hypersensitivity pneumonitis lasts for hours to days, while chronic one lasts for months.
Acute hypersensitivity pneumonitis is characterized by symptoms such as fever, body aches, chills, cough, and headaches, which can be mistaken for flu-like symptoms. On the other hand, chronic hypersensitivity pneumonitis can develop from long-term exposure to allergens in small amounts. In these cases, individuals may experience persistent coughs lasting for months, shortness of breath, fatigue, and significant weight loss. Chronic cases of HP can sometimes lead to digital clubbing due to prolonged lung damage and reduced oxygen levels.

Diagnosis of Hypersensitivity Pneumonitis?

The doctor will diagnose it depending on your medical history, presenting complaints, lung and blood tests, and X-rays.³

First, doctors will inquire about your symptoms, medical history, and family history. This comprehensive evaluation helps them gain perspective and enables an effective diagnosis.
Next, doctors often prescribe basic blood tests. In cases of acute hypersensitivity pneumonitis, they typically observe an elevation in the neutrophil count (a type of white blood cell). They may also find elevated levels of inflammatory markers such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), indicating inflammation.
In addition, doctors may perform an inhalation challenge test to assess your breathing response to specific substances. This test helps determine if exposure to certain triggers contributes to your condition.
Chest X-ray is commonly recommended to confirm the diagnosis. Abnormal findings are often observed in the X-rays of most hypersensitivity pneumonitis patients, providing valuable diagnostic information.
High-resolution CT (HRCT) scans of the chest can show specific patterns, such as ground-glass opacities, nodules, or fibrosis, that suggest HP.

It’s important to note that these diagnostic procedures may vary based on individual cases, and healthcare professionals will determine the most appropriate tests based on your specific situation.

Chest X-ray Findings:

Following are some Chest X-ray findings in hypersensitivity pneumonitis:

There are several small opacities throughout both lungs.
A reticular interstitial pattern may also be present.
Fibrotic changes may also be seen in later stages, such as honeycombing
Cardiomegaly (increase in heart size) may also be seen in the last stages of HP.

Chest X-ray of a bird fancier who presented with breathlessness. Diffuse lung opacities can be seen. Case courtesy of The Radswiki, Radiopaedia.org. From the case rID: 11512

Bronchoscopy:

The bronchoscopy allows for direct examination of the airways. Bronchoalveolar lavage (BAL) can collect fluid for analysis, and transbronchial biopsy can provide small tissue samples to support the diagnosis.

Surgical Lung Biopsy:

In certain cases, a surgical lung biopsy may be performed to obtain larger tissue samples for definitive confirmation of HP.

Treatment & Management

The following are the key points in treating and managing hypersensitivity pneumonitis.⁴

Avoidance of Antigen:

The first and best way to prevent it is to identify your allergen. Avoiding this antigen can help you control the symptoms.

Medication:

Your doctor may prescribe anti-inflammatory drugs to address the intense inflammation in hypersensitivity pneumonitis. Corticosteroids are the preferred group, and prednisone is often the initial treatment drug within this group.⁵

Pulmonary Rehabilitation:

Pulmonary rehabilitation is a great non-medicinal treatment for individuals living with hypersensitivity pneumonitis. It helps those seeking to boost their respiratory health and increase their quality of life by providing them with tailored programs best suited to their needs. Patients can benefit from specialized programs that combine various exercises, breathing techniques, and disease management strategies.

Alternative Stratigies for Chronic HP:

In chronic or progressive hypersensitivity pneumonitis (HP), where standard treatments are not effective, additional therapies may be considered. Azathioprine and mycophenolate mofetil can serve as steroid-sparing agents, helping to improve lung function when symptoms persist despite corticosteroid use and antigen avoidance. Rituximab⁶ and leflunomide have also shown potential benefits in difficult cases, and antifibrotic agents may be used in progressive cases with fibrosis.⁷

Lung Transplant:

Lung transplantation is an option for advanced HP, often offering positive medium-term outcomes. Studies indicate that patients with HP may experience a lower risk of post-transplant bronchiolitis obliterans syndrome (BOS) compared to those with other fibrotic lung diseases.⁸

Risk Factors & Prevention for Hypersensitivity Pneumonitis

The risk factors include repetitive exposure to allergens like dust, smoke, and mold. If you have any lung disease like asthma, you are more likely to get it. Similarly, people who smoke are also at risk of developing Hypersensitivity Pneumonitis.
You can minimize the risk of developing it by following these simple measures:

Identify and Avoid Triggers: Determine the specific substances or allergens causing your hypersensitivity pneumonitis and take steps to minimize or eliminate exposure to them.
Occupational Safety Measures: If your condition is work-related, follow safety protocols, wear protective equipment, and ensure proper ventilation in the workplace.
Maintain a Healthy Home Environment: Control humidity, address water leaks promptly, clean regularly, and ventilate your living space to reduce mold and allergen growth.
Pet and Bird Care: If you have hypersensitivity to animal dander or bird droppings, minimize your exposure. Keep pets out of the bedrooms or use air purifiers if needed.
Use Respiratory Protection: When working in environments with unavoidable triggers, use appropriate masks or respirators to reduce inhalation of allergens.
Consult healthcare professionals for personalized advice on prevention strategies for your specific situation.

What is the Life Expectancy in HP?

The life expectancy of people with this condition depends significantly on the particular type and severity of the medical condition. Fortunately, most acute-type sufferers can achieve a favorable outlook by removing the triggering allergen or antigen and resolving the condition. Chronic Hypersensitivity Pneumonitis can be a serious condition that could lead to irreversible lung damage if not managed appropriately. But with proper care, those living with Chronic type can still enjoy a fulfilling life for many years.

Conclusion:

It is a severe inflammatory response to allergens that can lead to severe lung disease. However, early detection and treatment are critical in preventing complications associated with HP and reserving overall lung function. Therefore, anyone experiencing unusual respiratory symptoms should seek medical attention as soon as possible to ensure early intervention before it causes irreversible damage.

Refrences

1
Costabel, U., Miyazaki, Y., Pardo, A., Koschel, D., Bonella, F., Spagnolo, P., … & Selman, M. (2020). Hypersensitivity pneumonitis. Nature Reviews Disease Primers, 6(1), 65.
2
Jose, J., & Craig, T. J. (201 ). Hypersensitivity pneumonitis. Allergy and Asthma: Practical Diagnosis and Management, 311-331.
3
Selman, M., Pardo, A., & King Jr, T. E. (2012). Hypersensitivity pneumonitis: insights in diagnosis and pathobiology. American journal of respiratory and critical care medicine, 186(4), 314-324.
4
Barnes, H., Troy, L., Lee, C. T., Sperling, A., Strek, M., & Glaspole, I. (2022). Hypersensitivity pneumonitis: Current concepts in pathogenesis, diagnosis, and treatment. Allergy, 77(2), 442-453.
5
Ejima M, Okamoto T, Suzuki T, Anzai T, Takahashi K, Miyazaki Y. Efficacy of treatment with corticosteroids for fibrotic hypersensitivity pneumonitis: a propensity score-matched cohort analysis. BMC Pulm Med. 2021 Jul 19;21(1):243. doi: 10.1186/s12890-021-01608-1. PMID: 34281549; PMCID: PMC8290597.
6
Ferreira M, Borie R, Crestani B, Rigaud P, Wemeau L, Israel-Biet D, Leroy S, Quétant S, Plantier L, Dalphin JC, Cottin V, Marchand-Adam S; of the OrphaLung network. Efficacy and safety of rituximab in patients with chronic hypersensitivity pneumonitis (cHP): A retrospective, multicentric, observational study. Respir Med. 2020 Oct;172:106146. doi: 10.1016/j.rmed.2020.106146. Epub 2020 Sep 9. PMID: 32971360.
7
Chandra D, Cherian SV. Hypersensitivity Pneumonitis. [Updated 2023 Jul 10]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK499918/
8
Kern RM, Singer JP, Koth L, Mooney J, Golden J, Hays S, Greenland J, Wolters P, Ghio E, Jones KD, Leard L, Kukreja J, Blanc PD. Lung transplantation for hypersensitivity pneumonitis. Chest. 2015 Jun;147(6):1558-1565. doi: 10.1378/chest.14-1543. PMID: 25412059; PMCID: PMC4451710.

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