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Melanie Cole (Host): Inhalation of organic antigens like bird feathers, mold, and hay over time can lead to the development of an environmental lung disease known as hypersensitivity pneumonitis. This can present with both a fibrotic and non-fibrotic phenotype, and clinical courses differ significantly between phenotypes.

Today, we will define diagnostic criteria based on clinical practice guidelines and discuss optimal management.

Welcome to UAB MedCast. I'm Melanie Cole. And joining me today is Dr. Kevin Dsouza. He's a pulmonologist and an assistant professor at UAB Medicine. Dr. Dsouza, it's a pleasure to have you join us today. I'd like you to start with a little overview of hypersensitivity pneumonitis, how prevalent it is, what you've been seeing in the trends. Speak about some of the common inhalation antigens. Tell us a little bit about the pathogenesis of this condition.

Dr. Kevin Dsouza: Yes. Hi, Melanie. It's great to be here. Hypersensitivity pneumonitis is prevalent about 11% per 100,000 in patients about 65 years and older. This is one of the databases we have. And primarily, it's an allergic reaction that the lungs have to an antigen, which is an allergen, so to speak. What happens is this antigen incites a response from the lungs, and that's when we have hypersensitivity, as the name says, pneumonitis, which is lung inflammation. There are various antigens which can cause this. Most commonly, it's mold from water damage in homes. It can also happen from bird feathers which can be either through poultry, exposure to poultry or chicken at homes, or close to homes, as well as down feathers, comforters, and beddings. This is commonly what we see in our clinic.

Melanie Cole (Host): Well, thank you for that. So why is it so important, as I spoke about in my intro, to categorize patients with fibrotic and progressive disease? Tell us a little bit about how it presents, because as you speak to other providers, they may not be as familiar as you are. And tell us the difference in presentation with both the fibrotic and non-fibrotic phenotypes.

Dr. Kevin Dsouza: Well, clinically, patients with hypersensitivity pneumonitis will complain of shortness of breath, and what's important is to elicit a history which can give you an idea of any antigens that the patient might be exposed to. Initially, there is no difference between presentations of fibrotic or non-fibrotic phenotype, that's because you have the acute inflammatory stage where an antigen presented to the lungs can incite an inflammatory response. What happens is, after that, this inflammation can either progress into a fibrotic phenotype.

Now, fibrotic phenotypes can have a poorer prognosis and can progress over time compared to a non-fibrotic phenotype where there is inflammation without any pulmonary fibrosis. Now, as I mentioned before, they behave differently. Fibrotic phenotypes progress over time and might need antifibrotic medications versus non-fibrotic phenotype, especially if we determine what the inciting antigen is and avoid the antigen altogether could have a better prognosis.

Melanie Cole (Host): Well, then, let's speak about differential diagnosis and why it's so challenging. Is there an absence, Dr. Dsouza, of international shared diagnostic guidelines and a lack of gold standard tests for hypersensitivity pneumonitis combined with these several clinical and radiologic overlapping features that could make it particularly challenging to differentiate this from other interstitial lung diseases?

Dr. Kevin Dsouza: To answer that question, Melanie, let's talk about the differentials. Obviously, any kind of interstitial lung disease is in the differential. And we then rely primarily on the history and the CT scan findings. Usually, on CT scan findings, we can find air trapping and multiple ground-glass opacities, which gives us an idea especially on expiratory images. This is a high-resolution CT scan and preferably done in prone positioning.

Now, there is a lack of international guidelines on the diagnosis of hypersensitivity pneumonitis. There are some guidelines, societal guidelines from the ATS and the CHEST, which goes down a diagnostic algorithm.

I think the most important thing, as I mentioned before, is trying to find an inciting antigen. Further testing could be a bronchoscopy with transbronchial biopsy and bronchial alveolar lavage versus a VATS biopsy. And all of this depends upon a multidisciplinary discussion involving a chest radiologist and pulmonary physicians.

Melanie Cole (Host): Well, then speak to us about optimal management. Tell us about any evidence that supports the drugs that you might commonly use, or the first medical options you would use at first diagnosis.

Dr. Kevin Dsouza: About one third of the patients can find the inciting antigen. And in my practice here, usually what happens is we look at the CT scan. On our first visit, we don't really find an inciting antigen. And then, what happens is once we look at the CT scan and do a multidisciplinary discussion, we'll call patients back and ask them to go through their homes, look for water damage, look for mold, pets, and feathers. The reason we want this is because finding an inciting antigen, we do it in about a third of our patients, has a much better prognosis because antigen avoidance is primarily the best form of treatment. In the acute phase of disease, we can also trial corticosteroids, which will help bring down the inflammation. Unfortunately, there is no real long-term data supporting immunosuppressive therapy on fibrotic phenotypes. We do this on occasion in patients, but the long-term data is weak.

Now, since the new antifibrotic medications are out and there is an expanded indication, especially in progressive fibrotic diseases, if a patient with fibrotic hypersensitivity pneumonitis progresses over time, we use antifibrotics, especially nintedanib, for the treatment of progressive fibrotic hypersensitivity pneumonitis.

Melanie Cole (Host): Dr. Dsouza, as we get ready to wrap up, what about recurrence? And you mentioned that some of the treatment is just identification of whatever the antigen is. Then, how does the patient take care of that situation? Is it something that you identify and then because can they have this recurrence or repeated recurrence if it's not addressed?

Dr. Kevin Dsouza: That is correct. They can have repeated recurrences, especially if the antigen is completely not eliminated. An example would be someone who's had water damage in the house and has mold growing and has that remediated, but just finds out that they have repeated water damage and that could cause a recrudescence of the disease. So, pivotal to the treatment of hypersensitivity pneumonitis is complete avoidance of the antigen. We've had cases, unfortunately, where we have asked our patients to move homes, because they were not able to completely eliminate the antigen.

Melanie Cole (Host): That's so interesting. As we wrap up, Dr. Dsouza, what would you like other providers to know about hypersensitivity pneumonitis and why it's so important to refer to the specialists at UAB if they have any questions?

Dr. Kevin Dsouza: I think hypersensitivity pneumonitis is a nuanced diagnosis which relies really on the history. The importance of sending patients to a center of excellence for interstitial lung diseases is that we have the benefit of a multidisciplinary team, which approaches these patients in a stepwise manner trying to figure out what the antigen is, recognizing what the CT scan patterns are, and discussing whether would be amenable to a biopsy or we have enough information to diagnose and treat a patient with just the CT scan and history.

It is important to also recognize sending patients earlier because, if they have a progressive fibrotic phenotype of hypersensitivity pneumonitis, we may have antifibrotic or clinical trial options for these patients.

Melanie Cole (Host): Thank you so much, Dr. Dsouza, for joining us today. And for more information or to refer a patient to UAB Medicine, you can call the MIST line at 1-800-UAB-MIST, or you can visit our website at uabmedicine.org/physician. And that concludes this episode of UAB MedCast. For updates on the latest medical advancements, breakthroughs, and research, follow us on your social channels. I'm Melanie Cole.