It has been hypothesized that the inciting agent can be part of a mixture of microbes, proteins, or other matter (e.g., dust). A previous study of a cohort of chronic, fibrotic HP patients found that fifteen percent of these patients revealed either the presence of a defined CTD or some autoimmune features suggestive of CTD. Some viral infections later in life may increase the risk of developing hypersensitivity pneumonitis. The pattern of organizing pneumonia relies on the presence of consolidation in a peribronchovascular and/or peripheral distribution, often seen with GGO and sometimes associated with a reverse halo pattern. A multidisciplinary (pulmonologists, radiologists, methodologists, pathologists, and patient) panel of experts from the ATS, JRS, and ALAT was composed to identify clinically important questions about diagnostic testing for HP among patients with newly identified ILD. Typical histopathological features of fibrotic HP; Either one of the following features in at least one biopsy site: 1. Therefore, the studies were kept in the final analysis. Lung biopsy often plays a pivotal role in ascertaining a diagnosis of HP. After reading our hypersensitivity pneumonitis Health Topic, you may be interested in additional information found in the following resources. The diagnostic yields were 96% (95% CI, 90–100%), 98% (95% CI, 98–99%), and 96% (95% CI, 93–99%) among patients with known or suspected HP, ILD, and DLD, respectively. (E) High-magnification photomicrograph illustrating another poorly formed nonnecrotizing granuloma (arrows) in the same biopsy specimen from a patient with nonfibrotic HP. Serum IgG testing against potential antigens associated with HP was suggested to identify potential exposures. If your condition is not adequately controlled by avoidance strategies or medicines and you develop serious complications, you may be a candidate for a lung transplant. Differences in our immune systems may explain why some people have strong reactions after breathing in certain substances, while others who breathe those same substances do not. In case of airways disease: the attenuation differences are accentuated due to the additional depiction of air trapping, • Term coined to replace the “headcheese” sign, as most individuals worldwide do not relate to the headcheese sign. Introduction. Table 5. The diagnosis of hypersensitivity pneumonitis Chest. ##SLB is infrequently considered in patients with nonfibrotic HP. Hematoxylin and eosin staining was used. Purely emphysematous forms of HP can be seen independently of smoking history (Figure E7) (85, 116, 131, 132), and fibrotic HP may also be diagnosed at the time of an acute exacerbation (Figure E8) (133). Smoking is not thought to increase the risk of developing hypersensitivity pneumonitis. The committee acknowledged the lack of standardization of serum IgG testing against potential antigens associated with HP, with no standardized, internationally accepted “HP panel” and different commercial kits being used by different laboratories. The latter features are usually observed in less fibrotic lung tissue. If your doctor is able to identify the environmental substance that causes your hypersensitivity pneumonitis, he or she will recommend that you adopt the following avoidance strategies. The fibrotic compatible-with-HP pattern varies in the patterns and/or distribution of lung fibrosis (e.g., basal and subpleural predominance, [G] upper-lung-zone predominance, [H] central [or peribronchovascular] predominance [arrows], or [I] fibrotic ground-glass attenuation seen alone or in association with small airway disease). All studies performed SLB and reported the diagnostic yield of the procedure; some also reported the frequency of adverse effects. The inflammatory infiltrate is typically polymorphic in that it includes smaller numbers of plasma cells and occasionally eosinophils in some patients. Along with suggestive clinical and radiological findings, history and timing of suspected antigen exposure are important elements for diagnostic confidence. It is unknown whether these situations represent unidentified exposure or whether these patients instead have features of HP that are primarily due to an independent, intrinsic/primary process. J.-C.D. served as a consultant for Bellerophon, Biogen, BMS, Boehringer Ingelheim, Fibrogen, Genentech, Gilead, Nitto, Promedior, Pure Tech Health, Respivant, Roche, Veracyte, and Zambon; and served on a data and safety monitoring board for Avalyn. There are no unique diagnostic laboratory tests for the diagnosis of hypersensitivity pneumonitis (HP). Always notify your doctor if your symptoms suddenly worsen. Hypersensitivity pneumonitis (HP), also known as extrinsic allergic alveolitis, is the result of non-IgE mediated immunologic inflammation. Bleeding was detected in 1% (95% CI, 0–1%). We initially considered ILD and DLD to be synonymous, but, on noting different diagnostic results in the two groups, we opted to analyze each separately. This effect was seen regardless of whether the study enrolled patients with nonfibrotic HP (17 studies; MD, 25%; 95% CI, 22–27%), fibrotic HP (16 studies; MD, 16%; 95% CI, 11–20%), or mixed populations with both nonfibrotic and fibrotic HP (21 studies; MD, 18%; 95% CI, 15–20%). If you have hypersensitivity pneumonitis, your body’s immune system reacts strongly to certain substances. In addition, new techniques like genomic classifiers and artificial intelligence to improve diagnosis and prognosis need to be assessed. These include 1) a cellular interstitial pneumonia accentuated around small airways (“bronchiolocentric”) accompanied by 2) a cellular chronic bronchiolitis, 3) a distinctive pattern of granulomatous inflammation, and 4) no histopathological features to suggest a more likely alternative (Figure 3 and Table 7) (3, 39, 44, 137, 141–144). However, the committee acknowledged that most medical centers, particularly community medical centers, currently cannot provide TBLC due to lack of equipment and expertise, nor do they have a large enough volume to justify establishing a TBLC program. 1. Voting results: recommendation for, 1; suggestion for, 20; no recommendation or suggestion, 4; suggestion against, 3; recommendation against, 0. Most studies enrolled patients with known HP, usually farmer’s lung disease or bird fancier’s disease, and determined the sensitivity and specificity of serum IgG testing against potential antigens associated with HP using ELISA or precipitins, the latter including double diffusion, immunoelectrophoresis, or electrosyneresis. For these reasons, a comprehensive multidisciplinary approach is important in diagnosing HP, particularly fibrotic HP; however, there remains substantial diagnostic disagreement across experienced MDD teams that likely reflects the absence of standardized diagnostic criteria (17). A face-to-face discussion among these various specialists is often necessary to make an accurate diagnosis. Acute hypersensitivity pneumonitis is the most common form of this condition. Magnification, 400×. Serum IgG testing against potential antigens associated with HP performed best when ELISA was the method used. (E) Photomicrograph from another section illustrated in A showing an isolated Schaumann body (arrow) in the fibrotic peribronchiolar interstitium. Normally, the immune system in the lungs monitors inhaled substances. Granulomatous inflammation completes the triad that allows a confident diagnosis of HP on the basis of histology alone, but the diagnostic value is heavily dependent on the qualitative features of the granulomas (Figure 4) (44, 142, 144). As a result, clinical practice varies substantially from region to region and among countries, agreement on HP diagnosis is poor (19), and some clinicians continue to use a consensus statement from nearly 30 years ago for guidance (6). Is the different T helper cell activity in sarcoidosis and extrinsic allergic alveolitis also reflected by the cellular bronchoalveolar lavage fluid profile? Serum IgG testing against potential antigens associated with HP performed similarly for ELISA and precipitin testing, and among all types of HP. K.C.W. If you have been diagnosed with subacute or chronic hypersensitivity pneumonitis, your doctor may recommend follow-up testing to see how well your treatment is working and if your disease is improving, stable, or worse. Table 3. Patients with DLD were more likely than patients with ILD to receive a non-ILD diagnosis like malignancy, infection, etc. Development and validation of a standard or personalized hypersensitivity panel was considered a priority for future clinical investigation. For a detailed description of the methods, see the online supplement. The optimal chest HRCT scan for characterizing HP should be a noncontrast examination, except in the context of acute respiratory decline, in which case CT angiography may be justified to detect acute pulmonary embolisms. Nine studies reported post-procedural exacerbation or respiratory failure (rare cases; 95% CI, 0–1%), 17 studies reported bleeding of any severity (11%; 95% CI, 7–15%), 18 studies reported severe bleeding (0%; 95% CI, 0–1%), and 23 studies reported pneumothoraces (10%; 95% CI, 8–13%). However, these categories are not easily demarcated, and their delineation has been variable and arbitrary in many studies. Performance indicators would have to focus on the fact that adequate deliberation about the management options has taken place. An Executive Summary of this document is available at http://www.atsjournals.org/doi/suppl/10.1164/rccm.202005-2032ST. Common symptoms and signs of both nonfibrotic and fibrotic HP include dyspnea, cough, and midinspiratory squeaks (or chirping rales or squawks) (32). To maximize their potential, HP-specific registries are needed. One example is farmer’s lung. The full text of 24 articles was reviewed, and 13 observational studies were selected to inform the guideline committee (14, 35, 257–267). Another study enrolled 46 patients with IPF and used a nine-item questionnaire, serum IgG testing against HP-associated antigens, and bronchial-challenge testing to identify potential inciting agents of HP. The chronic bronchiolitis characteristic of nonfibrotic HP is a continuum with bronchiolocentric interstitial pneumonia and comprise expansion of the peribronchiolar interstitium by the same lymphocyte-predominant inflammatory infiltrate, without or with only focal lymphoid aggregates that generally lack secondary germinal centers. Bronchiolar obstruction is also present in an HRCT pattern combining three different lung densities (GGO, lobules of decreased attenuation and vascularity, and normal-appearing lung) that is highly specific to fibrotic HP (123). If the condition goes untreated or is not well controlled over time, the chronic inflammation can cause irreversible scarring of the lungs that may severely impair their ability to function. Domestic reprint orders: Question 1: Should patients with newly detected ILD on chest radiographs or a CT scan of the chest, with or without an overt history of exposures capable of causing ILD in the patient’s environment at home, work, or elsewhere, be subjected to, Question 2: Should patients with newly detected ILD on chest radiographs or a CT scan of the chest, with or without an overt history of exposures capable of causing ILD in the patient’s environment at home, work, or elsewhere, undergo, Question 3: Should patients with newly detected ILD on chest radiographs or a CT scan of the chest, with or without a history of exposure capable of causing HP, undergo BAL, Question 4: Should patients with newly detected ILD on chest radiographs or a CT scan of the chest, with or without a history of exposure capable of causing HP, undergo, Question 5: Should patients with newly detected ILD on chest radiographs or a CT scan of the chest, with or without a history of exposure capable of causing HP, undergo, Question 6: Should patients with newly detected ILD on chest radiographs or a CT scan of the chest, with or without a history of exposure capable of causing HP, undergo. In the interim, the committee encourages clinicians to take a thorough history to identify potential exposures and to develop and use their own questionnaires to ensure routine inquiry about potential exposures whenever they evaluate a patient with newly detected ILD. The interstitial pneumonia is bronchiolocentric in distribution and comprises predominantly small lymphocytes. There was general agreement among members of the guideline committee that the diagnostic yield of TBLC is favorable, with 82–91% of patients potentially avoiding SLB. Methods: Systematic reviews were performed for six q … Polymorphisms in major histocompatibility complex class II, proteasomes, transporter proteins, and tissue inhibitors of matrix metalloproteinases have been associated with HP (99–106). The majority of individuals in this situation would want the suggested course of action, but a sizable minority would not. Serum IgG testing against potential antigens associated with HP distinguished HP from other ILDs with a sensitivity and specificity of 83% and 68%, respectively, derived from bivariate analysis of the summary receiver operator curve created by pooling four studies. Well-formed granulomas resembling those seen in sarcoidosis and granulomatous infections are uncommon and should raise the likelihood of other conditions if they predominate (134, 135). Learn how we are translating current research into improved health for people with hypersensitivity pneumonitis. Recommended radiation dose for the inspiratory volumetric acquisition: • Strong recommendation to avoid “ultra–low-dose CT” (<1 mSv), • Generic term referring to a patchwork of regions of differing attenuation on inspiratory CT images, • Term only used for description of inspiratory CT images, • Can reflect the presence of vascular disease, airway abnormalities, or ground-glass interstitial or airspace infiltration. For patients with newly identified ILD whose differential diagnosis includes nonfibrotic HP, the guideline committee recommends BAL with lymphocyte cellular analysis (recommendation, very low confidence in the estimated effects). suggests surgical lung biopsy only when all other diagnostic testing has not yielded a diagnosis (suggestion, very low confidence in the estimated effects). The immune systems of people with hypersensitivity pneumonitis are unable to shut down these normal inflammation processes, especially in the lung interstitium. (A–C) Poorly formed granulomas characteristic of hypersensitivity pneumonitis (HP) contrasted with (D and E) well-formed granulomas more typical of sarcoidosis. (B) Another photomicrograph illustrating giant cells in a patient with HP. Figure 3. Sources of Antigens Known to Cause HP. Conversely, patients with fibrotic HP are less likely to have an identified exposure and more frequently have an insidious and chronic onset of isolated pulmonary symptoms, fibrotic changes with or without more specific features of HP on chest imaging, and a nonspecific differential cell profile on BAL analysis (4, 105–107). For patients with newly identified ILD whose differential diagnosis includes nonfibrotic HP or fibrotic HP, the guideline committee makes no recommendation or suggestion for or against the use of a specific questionnaire to identify potential inciting agents of HP; instead, the guideline committee recommends the development and validation of a questionnaire. A multidisciplinary committee of international experts have released a new clinical practice guideline on the diagnosis of adult hypersensitivity pneumonitis (HP), an immune-mediated inflammatory lung and small airway disease. 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