Nationwide Study of the Epidemiology, Diagnosis, and Treatment of Hypersensitivity Pneumonitis in Korea

BACKGROUND

Hypersensitivity pneumonitis (HP) is a condition with an uncertain global incidence, and information on its diagnosis and management is limited. This study aimed to address these knowledge gaps.

METHODS

This study utilized customized claims data from the Health Insurance Review and Assessment Service (HIRA) in South Korea from January 2010, to December 2021. Patients with HP were identified based on the diagnosis code (International Classification of Diseases, 10th Revision, J67) between 2011 and 2020. Incident HP cases were defined as new HP claims, excluding those with claims in the previous year. The study examined various factors such as age, sex, comorbidities, diagnostic methods, and treatment patterns. Additionally, multivariate logistic regression analysis was performed to identify risk factors associated with treatment initiation.

RESULTS

A total of 8,678 HP incident cases were confirmed, with age- and sex-adjusted annual incidence rates ranging from 1.14/100,000 in 2020 to 2.16/100,000 in 2012. The mean age of patients with incident HP was 52 years, with a higher incidence observed among males. Additionally, the most common comorbidity was asthma. Bronchoscopy was performed on 16.9% of patients, and 25.4% of patients did not receive treatment within 1 year of diagnosis. Among those who received treatment, prednisone was the most used systemic steroid, and azathioprine was the most commonly used second-line immunosuppressant. Factors associated with treatment initiation included the female sex, having asthma or gastroesophageal reflux disease (GERD), and undergoing bronchoscopy.

CONCLUSION

This study provides valuable insights into the incidence, diagnosis, and treatment patterns of HP in South Korea using nationwide medical claims data.

Assessment of clinical relevance of antigen improves diagnostic accuracy of hypersensitivity pneumonitis

BACKGROUND

Exposure assessment is integral to the diagnosis of hypersensitivity pneumonitis (HP). Although the clinical relevance of exposed antigens is essential for the assessment, many of the previous guidelines or reports have only evaluated simple exposure histories or immunological tests. To overcome this problem, the Exposure Assessment Form (EAF) was developed as an assessment tool for classifying the exposure grade from G0 to G4. The EAF was modified from the description in the Japanese clinical practice guide 2022 for HP published by the Japanese Respiratory Society.

METHODS

One hundred and seventy-two consecutive patients with interstitial lung disease who underwent multidisciplinary discussion (MDD) at our hospital were retrospectively examined. We assessed whether the use of the EAF improved the diagnostic performance of the international guideline of HP. We also evaluated whether the exposure grade affected the prognosis of HP.

RESULTS

Even when a HP diagnosis was made with a confidence of 70% or higher according to the international guideline, less than half of these cases resulted in a final diagnosis of HP when the exposure grades were lower than G3. When the result of the EAF was integrated into the exposure definition of the international guideline, the specificity of the diagnostic performance improved, while sensitivity was maintained. Furthermore, HP patients with an exposure grade of G3 or higher showed a tendency to take a longer time to initiate medication.

CONCLUSIONS

This is the first study to evaluate the clinical relevance of possible antigens using the EAF. Assessing the exposure grade prevents overdiagnosis and improves the diagnostic performance of the international guideline.

[Workplace-associated fever]

INTRODUCTION

Febrile conditions often have an infectious etiology. However, there are also fevers associated with occupational exposures. A detailed occupational history can hold the key to the diagnosis. In the case of exposure to organic dusts, the development of hypersensitivity pneumonitis (HP) is possible. Thus, HP should be considered in the presence of interstitial lung disease of unclear etiology. Failure to recognize this can have dramatic consequences and, in extreme cases, lead to lung transplantation. Differentially, organic dust toxic syndrome (ODTS) must be considered. The syndrome of metal fume fever provoked by inhalation of inorganic substances is usually benign and self-limiting. The disease manifests with fever, cough, and flu-like sensations.

Hypersensitivity Pneumonitis: Challenges of a Complex Disease

Hypersensitivity pneumonitis (HP) is a complex interstitial lung disease caused by chronic inhalation of a wide variety of antigens in susceptible and sensitized individuals, commonly associated with an occupational exposure. An impressive number of inciting antigens causing hypersensitivity pneumonitis have been found to cover a wide range of occupations. As working practices have changed over time, especially in industrialized countries, new names for occupational HP have emerged. This review emphasizes the main diagnostic issues arising from the high variability of clinical presentation and the broad spectrum of causal antigens. Furthermore, it provides an overview of current methods to unveil possible causes of hypersensitivity pneumonitis, highlights HP's current diagnostic and treatment challenges and the remaining areas of uncertainty, and presents prevention strategies.

GDF15 as a potential biomarker to distinguish fibrotic from non-fibrotic hypersensitivity pneumonitis

Hypersensitivity Pneumonitis (HP) is an immune-mediated interstitial lung disease (ILD) characterized by fibrotic HP (fHP) or non-fibrotic HP (non-fHP). Fibrosis is associated with poor prognosis, emphasizing the need for biomarkers to distinguish fHP from non-fHP. This study aimed to determine the plasma levels of GDF15 in HP patients and assess its association with lung function and phenotype classification. GDF15 levels were quantified by ELISA in HP (n = 64), idiopathic pulmonary fibrosis (n = 54), and healthy control (n = 128) groups. Clinical, demographic, and functional data were obtained from medical records. High-resolution chest CT scans were used to classify HP patients into fHP and non-fHP groups. In addition, receiver operating characteristic analysis was performed to determine the cut-off point, sensitivity, and specificity. Our results revealed significantly elevated GDF15 levels in fHP compared to non-fHP (2539 ± 821 pg/ml versus 1783 ± 801 pg/ml; p = 0.009). The estimated cut-off point for plasma GDF15 levels to distinguish fHP from non-fHP was 2193.4 pg/ml (AUC 0.75). These findings suggest that GDF15 may serve as a valuable biomarker for differentiating between fHP and non-fHP, potentially indicating its involvement in lung fibrosis development in HP.

Vasoreactive pulmonary artery hypertension in non-fibrotic hypersensitive pneumonitis

Group III pulmonary hypertension (PH) is common in patients with hypersensitivity pneumonitis (HSP). Group I PH and vasoreactivity in HSP have not been reported. We describe a case of an elderly veterinarian woman who presented with progressive shortness of breath and desaturation on exertion. The patient was diagnosed with non-fibrotic HSP after consistent findings on chest CT, transbronchial biopsy and a positive HSP serological panel. The patient relocated her birds, and prednisone was started. Due to persistent symptoms, she underwent a right heart catheterisation, which showed PH with vasoreactivity; subsequently, nifedipine was started. Over a 9-month follow-up, there was an improvement in symptoms and a complete resolution of PH and CT scan changes. Our case highlights the rare possibility of group I PH in HSP. It illustrates the importance of confirming the aetiology of PH and initiating treatment early to resolve symptoms.

ILD-GAP combined with the monocyte ratio could be a better prognostic prediction model than ILD-GAP in patients with interstitial lung diseases

BACKGROUND

The ILD-GAP scoring system is known to be useful in predicting prognosis in patients with interstitial lung disease (ILD). An elevated monocyte count was associated with increased risks of IPF poor prognosis. We examined whether the ILD-GAP scoring system combined with the monocyte ratio (ILD-GAPM) is superior to the conventional ILD-GAP model in predicting ILD prognosis.

METHODS

In patients with ILD treated between April 2013 and April 2017, we were retrospectively assessed the relationships between baseline clinical parameters, including age, sex, Charlson Comorbidity Index score (CCIS), ILD diagnosis, blood biomarkers, pulmonary function test results, and disease outcomes. In ILD patients were included idiopathic pulmonary fibrosis (IPF), idiopathic nonspecific interstitial pneumonia (iNSIP), collagen vascular disease-related interstitial pneumonia (CVD-IP), chronic hypersensitivity pneumonitis (CHP), and unclassifiable ILD (UC-ILD). We also assessed the ability to predict prognosis was compared between the ILD-GAP and ILD-GAPM models.

RESULTS

A total of 179 patients (mean age, 73 years) were assessed. All of them were taken pulmonary function test, including percentage predicted diffusion capacity for carbon monoxide. ILD patients included 56 IPF cases, 112 iNSIP and CVD-IP cases, 6 CHP cases and 5 UC-ILD cases. ILD-GAPM provided a greater area under the receiver-operating characteristic curve (0.747) than ILD-GAP (0.710) for predicting 3-year ILD-related events. Furthermore, the log-rank test showed that the Kaplan-Meier curves in ILD-GAPM were significantly different by stage (P = 0.015), but not by stage in ILD-GAP (P = 0.074).

CONCLUSIONS

The ILD-GAPM model may be a more accurate predictor of prognosis for ILD patients than the ILD-GAP model.

Effect of warm and humid days on the positivity rate of anti-Trichosporon asahii antibody test for the diagnosis of summer-type hypersensitivity pneumonitis

BACKGROUND

Summer-type hypersensitivity pneumonitis (SHP) has been reported to occur during warm and humid summer seasons in Japan; however, the effect of weather conditions on SHP remains unknown. Anti-Trichosporon asahii antibody (TaAb) test is highly specific and useful for the diagnosing SHP. Therefore, we aimed to investigate the impact of weather conditions on SHP by examining the relationship between the positivity rate of TaAb and warm and humid days.

METHODS

TaAb test data from June 2013 to June 2020 were obtained from major commercial laboratories to determine the number of samples and positivity rate of TaAb by prefecture. Using the Japan Meteorological Agency database, we counted the warm and humid days (maximum temperature ≥25 °C and average humidity ≥80 %) for each prefecture. Negative binomial regression was employed to examine the relationship between the positivity rate of TaAb and the number of warm and humid days per month.

RESULTS

A total of 79,211 samples and 7626 positive samples (9.6 %) were identified. We found that the number of warm and humid days, 1 or 2 months prior to testing for TaAb, was associated with the positivity rate of the test. An increase in the positivity rate by 1.6 % and 2.9 % was observed with every 1-day increase in warm and humid days 1 month and 2 months before the test, respectively.

CONCLUSIONS

Our TaAb analysis revealed a significant increase in TaAb positivity 1 or 2 months after periods of warm and humid days.

Japanese clinical practice guide 2022 for hypersensitivity pneumonitis

Considering recently published two guidelines for the diagnosis of hypersensitivity pneumonitis (HP), the Japanese Respiratory Society (JRS) has now published its own Japanese clinical practice guide for HP. Major types of HP in Japan include summer-type, home-related, bird-related, farmer's lung, painter's lung, humidifier lung, and mushroom grower's lung. Identifying causative antigens is critical for increasing diagnostic confidence, as well as improving prognosis through appropriate antigen avoidance. This guide proposes a comprehensive antigen questionnaire including the outbreak sources reported in Japan. Drawing on the 2021 CHEST guideline, this guide highlights the antigen identification confidence level and adaptations for environmental surveys. The detection of specific antibodies against causative antigens is an important diagnostic predictor of HP. In Japan, the assessments of bird-specific IgG (pigeons, budgerigars) and the Trichosporon asahii antibody are covered by medical insurance. Although this guide adopts the 2020 ATS/JRS/ALAT guideline diagnostic criteria based on the combination of imaging findings, exposure assessment, bronchoalveolar lavage lymphocytosis, and histopathological findings, it added some annotations to facilitate the interpretation of the content and correlate the medical situation in Japan. It recommends checking biomarkers; seasonal changes in the KL-6 concentration (increase in winter for bird-related HP/humidifier lung and in summer for summer-type HP) and high KL-6 concentrations providing a basis for the suspicion of HP. Antigen avoidance is critical for disease management of HP. This guide also addresses the pharmacological management of HP, highlighting the treatment strategy for fibrotic HP including combination therapies with anti-inflammatory/immunosuppressive and antifibrotic drugs.

Masks of hypersensitivity pneumonitis in children

Hypersensitivity pneumonitis (HP), also known as extrinsic allergic alveolitis, is the most common interstitial lung disease in children, but remains rarely recognized in the pediatric population. Early recognition of triggering factors and a high index of suspicion of HP could lead to timely diagnosis and individualized treatment. This study aimed to present four clinical cases of HP reported between 2012 and 2022 in Lithuania to improve the suspicion of the disease in children.

Clinical characteristics of hypersensitivity pneumonitis: non-fibrotic and fibrotic subtypes

BACKGROUND

The presence of fibrosis is a criterion for subtype classification in the newly updated hypersensitivity pneumonitis (HP) guidelines. The present study aimed to summarize differences in clinical characteristics and prognosis of non-fibrotic hypersensitivity pneumonitis (NFHP) and fibrotic hypersensitivity pneumonitis (FHP) and explore factors associated with the presence of fibrosis.

METHODS

In this prospective cohort study, patients diagnosed with HP through a multidisciplinary discussion were enrolled. Collected data included demographic and clinical characteristics, laboratory findings, and radiologic and histopathological features. Logistic regression analyses were performed to explore factors related to the presence of fibrosis.

RESULTS

A total of 202 patients with HP were enrolled, including 87 (43.1%) NFHP patients and 115 (56.9%) FHP patients. Patients with FHP were older and more frequently presented with dyspnea, crackles, and digital clubbing than patients with NFHP. Serum levels of carcinoembryonic antigen, carbohydrate antigen 125, carbohydrate antigen 153, gastrin-releasing peptide precursor, squamous cell carcinoma antigen, and antigen cytokeratin 21-1, and count of bronchoalveolar lavage (BAL) eosinophils were higher in the FHP group than in the NFHP group. BAL lymphocytosis was present in both groups, but less pronounced in the FHP group. Multivariable regression analyses revealed that older age, <20% of lymphocyte in BAL, and ≥1.75% of eosinophil in BAL were risk factors for the development of FHP. Twelve patients developed adverse outcomes, with a median survival time of 12.5 months, all of whom had FHP.

CONCLUSIONS

Older age, <20% of lymphocyte in BAL, and ≥1.75% of eosinophil in BAL were risk factors associated with the development of FHP. Prognosis of patients with NFHP was better than that of patients with FHP. These results may provide insights into the mechanisms of fibrosis in HP.

When to panic about a panic attack: A challenging case of hypersensitivity pneumonitis

The COVID-19 pandemic has created diagnostic difficulties with the increase in mental health illnesses that often present with nonspecific symptoms, like hypersensitivity pneumonitis. Hypersensitivity pneumonitis is a complex syndrome of varying triggers, onset, severity, and clinical manifestations that can be challenging to diagnose in many cases. Typical symptoms are nonspecific and can be attributed to other entities. There are no pediatric guidelines, which contributes to diagnostic difficulties and delays in treatment. It is particularly important to avoid diagnostic biases, have an index of suspicion for hypersensitivity pneumonitis, and to develop pediatric guidelines as outcomes are excellent when diagnosed and treated promptly. This article discusses hypersensitivity pneumonitis with a focus on the causes, pathogenesis, diagnostic approach, outcomes, and prognosis while using a case to illustrate the diagnostic difficulties worsened by the COVID-19 pandemic.

Concurrent features of sarcoidosis and hypersensitivity pneumonitis in two patients exposed to fungal antigens

BACKGROUND

Sarcoidosis and hypersensitivity pneumonitis (HP) are two distinct clinical entities that share granulomatous inflammation, although each of them has specific clinical, radiologic and pathologic profiles. Coexistence of the two diseases have been described, suggesting, at least in some cases, a common biologic background.

CASE PRESENTATION

We describe two patients showing the concurrent diagnosis of sarcoidosis and hypersensitivity pneumonitis. Case 1: a 51-year old never smoker man had a history of occupational exposure, episodes of acute exacerbations and positive serum precipitins to Penicillium spp suggestive of HP, while the positivity of serum angiotensin converting enzyme (ACE) favored sarcoidosis. Case 2: a 42-year old non-smoker woman with occasional finding of enlarged mediastinal lymph nodes had a history of domestic exposure to molds and positive serum precipitins to Aspergillus spp suggestive of HP. In both cases high resolution computed tomography (HRCT) together with broncoscopy findings allowed to maintain both the diagnoses: HRCT showed both enlarged hilar/mediastinal limph nodes and intersitial lung involvement typical of HP; bronchoalveolar lavage presented marked lymphocytosis and granulomatous nodal lesions were observed at transbronchial needle aspiration.

CONCLUSIONS

Sarcoidosis and HP share some clinical findings and the differential diagnosis may be difficult. Our cases suggest that a common trait may be responsible for the concurrent diagnosis of sarcoidosis and hypersensitivity pneumonitis in the same patient.

Impact of antigen identification on transplant free survival in interstitial lung disease

INTRODUCTION

Antigen identification impacts diagnosis as well as prognosis in patients with hypersensitivity pneumonitis. An antigen may also be present in other etiologies of interstitial lung disease, however it is unknown whether identification impacts survival.

METHODS

We evaluated a retrospective cohort in order to determine if antigen identification affects transplant free survival in patients with hypersensitivity pneumonitis, idiopathic pulmonary fibrosis, connective tissue disease interstitial lung disease, and interstitial pneumonia with autoimmune features. Only patients with definite or high probability of hypersensitivity pneumonitis by American Thoracic Society guidelines were included in the analysis.

RESULTS

Transplant free survival was improved with antigen identification in patients with hypersensitivity pneumonitis but not in patients with idiopathic pulmonary fibrosis, connective tissue disease interstitial lung disease, and interstitial pneumonia with autoimmune features.

CONCLUSION

Our study suggests that removal of identified antigen in interstitial lung diseases other than hypersensitivity pneumonitis may not be impactful. Additionally, it further suggests that definitive diagnosis of hypersensitivity pneumonitis with bronchoalveolar lavage and transbronchial biopsy may be beneficial prior to recommending antigen removal.

Serum Specific Antibodies Do Not Seem to Have an Additional Role in the Diagnosis of Hypersensitivity Pneumonitis

BACKGROUND

We aimed to investigate the contribution of serum IgG testing to the history of exposure in the diagnosis of fibrotic hypersensitivity pneumonitis.

METHODS

A single-center, retrospective, cross-sectional study including 63 patients pathologically diagnosed with fibrotic hypersensitivity pneumonitis in line with the guidelines of the American Thoracic Society. Descriptive statistics were presented and Kappa statistic was performed to evaluate the compatibility between panel and the history of exposure.

RESULTS

The median age was 63 (22-81) years and 34 (54%) were male. Forty-six patients (73%) had a positive history of exposure. Thirty-nine patients (61.9%) had a positive HP/Avian panel. The most common exposure agent was mold (34.9%), followed by parakeet (31.7%). The antibody detected the most was penicillium chrysogenum lgG (36.5%), followed by aspergillus fumigatus (31.8%). There was no compatibility between HP/Avian panel and history of exposure (kappa coefficient= 0.18, p= 0.14). When the exposure was only assessed based on the history, 4 (6.35%) patients were diagnosed as fibrotic hypersensitivity pneumonitis with low confidence, 6 (9.52%) with moderate confidence, 11 (17.46%) with high confidence and 42 (66.67%) with definite confidence; whereas 4 (6.35%) patients were diagnosed as fibrotic hypersensitivity pneumonitis with low confidence, 6 (9.52%) with moderate confidence, 9 (14.29%) patients with high confidence and 44 (69.84%) patients with definite confidence if exposure was evaluated with history and/or panel.

CONCLUSIONS

Serum specific precipitating antibody panel does not seem to provide additional value to the history of exposure in the diagnosis of fibrotic hypersensitivity pneumonitis.

Moldy Hazelnut Husk and Shell Related Hypersensitivity Pneumonitis: A Possible Novel Occupational Causative Agent

Hypersensitivity pneumonitis (HP) is a complex immune-mediated interstitial lung disease (ILD) triggered by inhalation exposure to environmental or occupational antigens in genetically susceptible individuals. Novel exposure sources and antigens are frequently identified. However, the causative agent remains unidentified in nearly half of HP cases. Early diagnosis for nonfibrotic-HP and quitting the exposure may prevent the disease progression to fibrotic forms and related complications. Here, we present two cases of HP associated with mold exposure in hazelnut husks, leaves, and shells in hazelnut agriculture.

Diagnostic Utility of Bronchoalveolar Lavage Lymphocytosis in Patients with Interstitial Lung Diseases

BACKGROUND

Interstitial lung diseases (ILDs) are extremely challenging in terms of diagnosis. Extreme bronchoalveolar lavage (BAL) lymphocytosis is thought to strongly point towards the diagnosis of hypersensitivity pneumonitis (HP).

OBJECTIVES

Explore the range of different ILD that can present with BAL lymphocytosis, including cases of pronounced lymphocytosis and its diagnostic utility.

METHODS

Patients with ILD that were subjected to BAL were identified retrospectively from a cohort of consecutive patients.

RESULTS

BAL lymphocytosis ≥20% was recorded in 106 patients (27%), while pronounced BAL lymphocytosis ≥40% was recorded in 49 patients (12.5%). The most common diagnoses in patients with BAL lymphocytosis ≥20% and ≥40%, were HP (32.1%), connective tissue disease (CTD)-ILD (26.4%), sarcoidosis (16%), and HP (38.8%), CTD-ILD (24.5%), sarcoidosis (14.3%), respectively.

CONCLUSIONS

Neither the presence nor the degree of BAL lymphocytosis can point to a specific diagnosis.

Machine learning-based metabolism-related genes signature, single-cell RNA sequencing, and experimental validation in hypersensitivity pneumonitis

Metabolism is involved in the pathogenesis of hypersensitivity pneumonitis. To identify diagnostic feature biomarkers based on metabolism-related genes (MRGs) and determine the correlation between MRGs and M2 macrophages in patients with hypersensitivity pneumonitis (HP). We retrieved the gene expression matrix from the Gene Expression Omnibus database. The differentially expressed MRGs (DE-MRGs) between healthy control (HC) and patients with HP were identified using the "DESeq2" R package. The "clusterProfiler" R package was used to perform "Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses" on DE-MRGs. We used machine learning algorithms for screening diagnostic feature biomarkers for HP. The "receiver operating characteristic curve" was used to evaluate diagnostic feature biomarkers' discriminating ability. Next, we used the "Cell-type Identification by Estimating Relative Subsets of RNA Transcripts" algorithm to determine the infiltration status of 22 types of immune cells in the HC and HP groups. Single-cell sequencing and qRT-PCR were used to validate the diagnostic feature biomarkers. Furthermore, the status of macrophage polarization in the peripheral blood of patients with HP was determined using flow cytometry. Finally, the correlation between the proportion of M2 macrophages in peripheral blood and the diagnostic biomarker expression profile in HP patients was determined using Spearman analysis. We identified a total of 311 DE-MRGs. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis showed that DE-MRGs were primarily enriched in processes like steroid hormone biosynthesis, drug metabolism, retinol metabolism, etc. Finally, we identified NPR3, GPX3, and SULF1 as diagnostic feature biomarkers for HP using machine learning algorithms. The bioinformatic results were validated using the experimental results. The CIERSORT algorithm and flow cytometry showed a significant difference in the proportion of M2 macrophages in the HC and HP groups. The expression of SULF1 was positively correlated with the proportion of M2-type macrophages. In addition, a positive correlation was observed between SULF1 expression and M2 macrophage proportion. Finally, we identified NPR3, GPX3, and SULF1 as diagnostic feature biomarkers for HP. Further, a correlation between SULF1 and M2 macrophages was observed, providing a novel perspective for treating patients with HP and future studies.

Pathologic Criteria for the Diagnosis of Usual Interstitial Pneumonia vs Fibrotic Hypersensitivity Pneumonitis in Transbronchial Cryobiopsies

Transbronchial cryobiopsy (TBCB) is increasingly used for the diagnosis of fibrosing interstitial pneumonias, but there are few detailed descriptions of the pathologic findings in such cases. It has been proposed that a combination of patchy fibrosis and fibroblast foci with an absence of alternative features is diagnostic of usual interstitial pneumonia (UIP; ie, idiopathic pulmonary fibrosis [IPF]) in TBCB. In this study, we reviewed 121 TBCB in which a diagnosis of fibrotic hypersensitivity pneumonitis (FHP; n = 83) or IPF (n = 38) was made by multidisciplinary discussion and evaluated a range of pathologic features. Patchy fibrosis was found in 65 of 83 (78%) biopsies from FHP and 32of 38 (84%) biopsies from UIP/IPF cases. Fibroblast foci were present in 47 of 83 (57%) FHP and 27 of 38 (71%) UIP/IPF cases. Fibroblast foci/patchy fibrosis combined did not favor either diagnosis. Architectural distortion was seen in 54 of 83 (65%) FHP and 32 of 38 (84%) UIP/IPF cases (odds ratio [OR] for FHP, 0.35; P = .036) and honeycombing in 18 of 83 (22%) and 17 of 38 (45%), respectively (OR, 0.37; P = .014). Airspace giant cells/granulomas were present in 13 of 83 (20%) FHP and 1 of 38 (2.6%) UIP/IPF cases (OR for FHP, 6.87; P = .068), and interstitial giant cells/granulomas in 20 of 83 (24%) FHP and 0 of 38 (0%) UIP/IPF (OR, 6.7 x 106; P = .000). We conclude that patchy fibrosis plus fibroblast foci can be found in TBCB from both FHP and UIP/IPF. The complete absence of architectural distortion/honeycombing favors a diagnosis of FHP, as does the presence of airspace or interstitial giant cells/granulomas, but these measures are insensitive, and many cases of FHP cannot be separated from UIP/IPF on TBCB.

Progressive fibrotic interstitial lung disease

Many interstitial lung diseases (ILDs) share mechanisms that result in a progressive fibrosing phenotype. In Brazil, the most common progressive fibrosing interstitial lung diseases (PF-ILDs) are chronic hypersensitivity pneumonitis, idiopathic pulmonary fibrosis, unclassified ILD, and connective tissue diseases. PF-ILD is seen in approximately 30% of patients with ILD. Because PF-ILD is characterized by disease progression after initiation of appropriate treatment, a diagnosis of the disease resulting in fibrosis is critical. Different criteria have been proposed to define progressive disease, including worsening respiratory symptoms, lung function decline, and radiological evidence of disease progression. Although the time elapsed between diagnosis and progression varies, progression can occur at any time after diagnosis. Several factors indicate an increased risk of progression and death. In the last few years, antifibrotic drugs used in patients with idiopathic pulmonary fibrosis have been tested in patients with PF-ILD. The effects of nintedanib and placebo have been compared in patients with PF-ILD, a mean difference of 107.0 mL/year being observed, favoring nintedanib. The U.S. Food and Drug Administration and the Brazilian Health Regulatory Agency have approved the use of nintedanib in such patients on the basis of this finding. Pirfenidone has been evaluated in patients with unclassified ILD and in patients with other ILDs, the results being similar to those for nintedanib. More studies are needed in order to identify markers of increased risk of progression in patients with ILD and determine the likelihood of response to treatment with standard or new drugs.

Effect of the 2020 hypersensitivity pneumonitis guideline on the pathologic diagnosis of interstitial pneumonia

It was reported that the 2020 guideline for hypersensitivity pneumonitis (HP) might result in the overdiagnosis of fibrotic HP (fHP). fHP and other types of interstitial pneumonias have several overlapping characteristics, and a high diagnostic concordance rate of fHP is rarely obtained. Therefore, we investigated the impact of the 2020 HP guideline on the pathological diagnosis of cases previously diagnosed as interstitial pneumonia. We identified 289 fibrotic interstitial pneumonia cases from 2014 to 2019 and classified them into four categories according to the 2020 HP guideline: typical, probable, and indeterminate for fHP and alternative diagnosis. The original pathological diagnosis of 217 cases were compared to their classification as either typical, probable, or indeterminate for fHP according to the 2020 guideline. The clinical data, including serum data and pulmonary function tests, were compared among the groups. Diagnoses changed from non-fHP to fHP for 54 (25%) of the 217 cases, of which, 8 were typical fHP and 46 were probable fHP. The ratio of typical and probable fHP cases to the total number of VATS cases was significantly lower when using transbronchial lung cryobiopsy (p < 0.001). The clinical data of these cases bore a more remarkable resemblance to those diagnosed as indeterminate for fHP than to those diagnosed as typical or probable. The pathological criteria in the new HP guidelines increase the diagnosis of fHP. However, it is unclear whether this increase leads to overdiagnosis, and requires further investigation. Transbronchial lung cryobiopsy may not be helpful when using the new criteria to impart findings for fHP diagnosis.

Novel occupational causes of hypersensitivity pneumonitis

PURPOSE OF REVIEW

Hypersensitivity pneumonitis (HP) remains a challenging diagnosis, and a cause is not established in up to 50% of cases. This paper aims to update clinicians on traditional and novel occupational causes of HP, and clinical tools for identifying of causative exposures and antigens.

RECENT FINDINGS

Metalworking fluid has become the most frequently cited occupational cause of HP, though geographical variations in exposures exist. Occupational HP is usually associated with work-related symptoms. Systematically derived questionnaires and compendia for HP have been developed for use in cryptogenic disease, though have previously lacked validation; these may help identify inciting antigens or relevant occupational exposures.

SUMMARY

Clinicians should enquire about job roles and work-relatedness of symptoms when considering a diagnosis of HP. Outbreaks of metalworking fluid associated HP from around the world are well described, so clinicians should remain vigilant. The usual classification for causative antigen includes animal and plant proteins, fungi, bacteria, low-molecular weight chemicals and metals; however novel occupational exposures and work processes are frequently reported.

An unexpected and unusual cause of pulmonary hypertension in a patient with hypersensitivity pneumonitis: a partial anomalous pulmonary venous connection causing pulmonary artery hypertension

Partial anomalous pulmonary venous connection (PAPVC) occurs when any pulmonary vein, but not all, drains directly into the right atrium or its venous tributaries. PAPVC can very rarely present as an individual cause of pulmonary artery hypertension. Here we are presenting the case of a 41-year-old farmer with a history of exertional dyspnea for the past 3 years, which increased over 6 months. Chest high-resolution computed tomography was suggestive of non-fibrotic hypersensitivity pneumonitis. Hence, the patient was started on systemic steroids, with which the patient's oxygen saturation improved. On 2D echocardiography, the right ventricle systolic pressure was 48 + right atrial pressure. Right heart catheterization showed a mean pulmonary artery pressure of 73 mmHg and pulmonary vascular resistance of 8.7. On further evaluation, a computed tomography pulmonary angiogram was done, which surprisingly revealed the left superior pulmonary vein draining into the left brachiocephalic vein.

Occupational hypersensitivity pneumonia

Hypersensitivity pneumonitis (HP) is an immunological lung disease that affects individuals who are sensitive and susceptible to occupational and environmental exposures. While clinical and radiological findings may resemble other interstitial lung diseases, identifying the causative agents can aid in the differential diagnosis. However, this can be challenging and may result in delayed diagnosis and poor prognosis. A gold standard test for diagnosis is currently unavailable, and therefore, a multidisciplinary approach involving a clinician, radiologist, and pathologist is necessary. Avoiding exposure is the first step in treatment, with immunosuppressive therapeutics also being used. Antifibrotic agents show promise for future treatment approaches. Despite recent advancements in data and guidelines, knowledge about managing occupational HP remains limited. This review provides a summary of the epidemiological, clinical, and radiological findings, as well as diagnostic and treatment principles of occupational HP based on current literature.

The Effects of Interstitial Lung Diseases on Alveolar Extracellular Vesicles Profile: A Multicenter Study

Diagnosis of interstitial lung diseases (ILD) is difficult to perform. Extracellular vesicles (EVs) facilitate cell-to-cell communication, and they are released by a variety of cells. Our goal aimed to investigate EV markers in bronchoalveolar lavage (BAL) from idiopathic pulmonary fibrosis (IPF), sarcoidosis and hypersensitivity pneumonitis (HP) cohorts. ILD patients followed at Siena, Barcelona and Foggia University Hospitals were enrolled. BAL supernatants were used to isolate the EVs. They were characterized by flow cytometry assay through MACSPlex Exsome KIT. The majority of alveolar EV markers were related to the fibrotic damage. CD56, CD105, CD142, CD31 and CD49e were exclusively expressed by alveolar samples from IPF patients, while HP showed only CD86 and CD24. Some EV markers were common between HP and sarcoidosis (CD11c, CD1c, CD209, CD4, CD40, CD44, CD8). Principal component analysis distinguished the three groups based on EV markers with total variance of 60.08%. This study has demonstrated the validity of the flow cytometric method to phenotype and characterize EV surface markers in BAL samples. The two granulomatous diseases, sarcoidosis and HP, cohorts shared alveolar EV markers not revealed in IPF patients. Our findings demonstrated the viability of the alveolar compartment allowing identification of lung-specific markers for IPF and HP.

Clinical characteristics and outcomes of hypersensitivity pneumonitis in South Korea

BACKGROUND

Hypersensitivity pneumonitis (HP) is an interstitial lung disease (ILD) that results from an immune-mediated reaction involving various antigens in susceptible individuals. However, the clinical characteristics and outcomes of HP in South Korea are not well understood.

OBJECTIVES

This study was conducted to identify the clinical characteristics and outcomes of HP in South Korea.

DESIGN

This is a retrospective observational study investigating patients with pathologically confirmed HP at our center, along with a comprehensive review of published HP cases in the Republic of Korea.

METHODS

This retrospective study analyzed 43 patients with pathologically proven HP at a single tertiary hospital in Korea between 1996 and 2020. In addition, case reports of HP published in Korea were collected. The clinical characteristics, etiologies, treatment, and outcomes of patients from our center, as well as case reports, were reviewed. Patients from our hospital were divided into fibrotic and nonfibrotic subtypes according to the ATS/JRS/ALAT guidelines.

RESULTS

Among 43 patients with biopsy-proven HP, 12 (27.9%) and 31 (72.1%) patients were classified into the fibrotic and nonfibrotic subtypes, respectively. The fibrotic HP group was older (64.6 ± 8.5 versus 55.2 ± 8.3, p = 0.002) with less frequent complaints of fever (0% versus 45.2%, p = 0.013) compared to the nonfibrotic HP group. The most common inciting antigen was household mold (21, 48.8%), followed by inorganic substances (6, 14.0%). Inciting antigens were not identified in eight (18.6%) patients. Treatment of corticosteroids was initiated in 34 (79.1%) patients. An analysis of 46 patients from Korea by literature review demonstrated that reported cases were relatively younger and drugs were the most common etiology compared to our cohort.

CONCLUSION

The analysis of reported cases, as well as our cohort, showed that exposure history and clinical manifestations are heterogeneous for patients with HP in South Korea.

Hypersensitivity Pneumonitis: An Updated Diagnostic Guide for Internists

This summary highlights updated definitions, terminology, and classification systems proposed in the diagnosis of hypersensitivity pneumonitis. Clinical presentation, epidemiology, and pathophysiology are reviewed from the most recent data. Radiographic and histopathologic diagnostic criteria are presented in a manner relevant to the practice of general medicine internists, including new guideline recommendations. The role of adjunctive tests, such as serum IgG testing, bronchoalveolar lavage lymphocyte analysis, and pulmonary function testing is discussed in the context of supporting diagnostic confidence for hypersensitivity pneumonitis diagnosis. Finally, new diagnostic algorithms are synthesized and applied to the general internal medicine setting.

Impact of number and type of identified antigen on transplant-free survival in hypersensitivity pneumonitis

Background

Identification of inciting antigen can affect diagnostic confidence, quality of life, and prognosis in patients with HP. It is unknown whether the number and type of antigen affect results of diagnostic testing or prognosis, whether antigen identified by clinical history alone affects prognosis, and whether feather exposure is associated with outcomes similar to those of other antigens.

Methods

To evaluate whether the number or type of antigen identified by clinical history alone affects clinical outcomes, we evaluated a retrospective cohort of patients with a high or definite probability of HP based on recent guidelines.

Results

In our retrospective cohort, 136 patients met high or definite probability of HP and were included in the analysis. Median transplant-free survival was better in patients with antigen identified on clinical history alone than patients without identified antigen. Feather exposure was associated with improved TFS compared to patients without antigen identified; there was no difference in TFS between patients with feather exposure and either mold or live bird exposure. Mold antigen was associated with increased risk of fibrotic HP compared to avian antigen. Among patients with identified antigen, the number and type of antigen did not affect TFS.

Discussion

Our study suggests that clinical history is adequate for providing prognostic information to patients with HP and classifying the diagnostic probability of HP according to recent guidelines. Feather exposure should be considered an inciting antigen in patients with ILD.

YKL-40 and KL-6 Levels in Serum and Sputum of Patients Diagnosed With Hypersensitivity Pneumonitis

BACKGROUND

YKL-40 (chitinase 3-like-1) and Krebs von den Lungen-6 (KL-6) are 2 promising biomarkers that may have an important role in the management of interstitial lung diseases (ILD).

OBJECTIVE

The aim of this study was to investigate the values of KL-6 and YKL-40 as biomarkers in the diagnosis and prognosis of patients with hypersensitivity pneumonitis (HP).

METHODS

A cross-sectional study conducted in 49 patients diagnosed with HP due to exposure to birds (n = 32) or fungi (n = 17), 48 patients with other ILD, and 67 healthy volunteers. Patients with HP were divided into fibrotic and nonfibrotic. Serum and sputum YKL-40 and KL-6 levels were determined using commercial enzyme-linked immunosorbent assay kits. Receiver operating characteristic (ROC) curves were used to determine the sensitivity and specificity of both biomarkers for the diagnosis of HP. Pulmonary function tests were performed in patients during follow-up.

RESULTS

KL-6 and YKL-40 levels were significantly higher in serum of patients with HP exposed to birds with a fibrotic pattern than in controls (P < .0001 and .0055, respectively). Serum KL-6 levels were also significantly higher in patients with fibrotic HP exposed to fungi compared with the control group (P = .0001). In patients with HP exposed to fungi, sputum KL-6 and YKL-40 levels were higher in those with a fibrotic pattern (P = .0289 and .016, respectively). ROC analysis showed that the range between 55-121 ng/mL for serum YKL-40 levels and 346-1441 U/mL for serum KL-6 levels had the best sensitivity and specificity for discriminating between patients with HP, healthy controls, and patients with idiopathic pulmonary fibrosis (IPF). In patients with HP, serum KL-6 levels correlated negatively with total lung capacity (r = -0.485; P = .0103) and diffusing capacity of the lungs for carbon monoxide (r = -0.534; P = .0002) at 12 months.

CONCLUSIONS

Both KL-6 and YKL-40 proteins seem to be capable of distinguishing patients with HP from healthy individuals and from patients with IPF. Their sensitivity and specificity confirm their potential role as biomarkers. KL-6 may also be a predictor of disease progression.

Management of fibrotic hypersensitivity pneumonitis

PURPOSE OF REVIEW

Recent guidelines have updated the classification of hypersensitivity pneumonitis, stratifying by the presence or absence of fibrosis as either fibrotic or nonfibrotic hypersensitivity pneumonitis. Fibrotic hypersensitivity pneumonitis represents up to 10% of interstitial lung disease in large cohort studies, and is occasionally even more common in some regions; however, there are many unknown aspects to the diagnosis and management. The goal of this review article is to summarize the management of fibrotic hypersensitivity pneumonitis.

RECENT FINDINGS

Historically, the only treatment options for patients with hypersensitivity pneumonitis were antigen avoidance and corticosteroids, although other immunosuppressive therapies are increasingly endorsed by experts in the field. There is accumulating evidence that antifibrotic medications can be useful as a second-line therapy in some patients with fibrotic hypersensitivity pneumonitis who have progression despite immunosuppression. There remains no direct comparison of immunosuppressive vs. antifibrotic medication for the management of fibrotic hypersensitivity pneumonitis, but some clinical, radiological and pathological features may suggest greater likelihood of benefit from one option or the other.

SUMMARY

We anticipate that future treatment of fibrotic hypersensitivity pneumonitis will consider a variety of patient features to suggest the most prominent underlying biology that will then be used to guide initial pharmacotherapy; however, additional data are still needed.

Hypersensitivity Pneumonitis Caused by Exposure to a Gray Parrot (Psittacus erithacus)

A 73-year-old woman complaining of cough and dyspnea was admitted to our hospital. High-resolution computed tomography chest revealed patchy ground-glass attenuation in the upper lung field. The patient suffered an asthma attack and was diagnosed with allergic pneumonitis; prednisolone was administered for treatment. Bird-related hypersensitivity pneumonitis was suspected, as she had a gray parrot (Psittacus erithacus) and a budgerigar (Melopsittacus undulatus) at home. An immunoblotting analysis with the patient's serum demonstrated IgG-binding fractions to the gray parrot's feathers only; no binding was noted with the budgerigar antigens. The patient was conclusively diagnosed with hypersensitivity pneumonitis related to exposure to a gray parrot.

Diagnosis of Hypersensitivity Pneumonitis: Review and Summary of American College of Chest Physicians Statement

Assessment of lung biopsies for the diagnosis of hypersensitivity pneumonitis (HP) is one of the most difficult diagnostic problems for surgical pathologists. It is a form of interstitial lung disease resulting from an immune reaction provoked by an inhaled antigen in susceptible individuals. Although this definition sounds simple, in practice, the diagnosis of HP can be challenging. To address these issues, the American College of Chest Physicians (CHEST) has recently published a guideline for the diagnosis of HP. In this review, we will explore the multidisciplinary diagnostic evaluation of HP with a focus on the pathologic features as outlined in the CHEST guidelines. The histologic criteria are divided into 4 diagnostic categories: (1) Typical nonfibrotic HP or fibrotic HP; (2) Compatible with nonfibrotic HP or fibrotic HP; (3) Indeterminate for nonfibrotic or fibrotic HP; and (4) Alternative Diagnosis. It is important to emphasize that patterns 1 to 3 do not represent discrete histologic entities or pathologic diagnoses. Rather, these categories are meant to serve as a practical guide for organizing a complex set of overlapping histologic patterns into an integrated diagnostic framework for facilitating multidisciplinary discussion. High-resolution computed tomography features are also summarized, emphasizing how the correlation of lung biopsies with computed tomography findings can help to favor the diagnosis, particularly in cases where biopsies are not typical for HP. This review highlights details of the histologic spectrum of HP as well as the utility of different types of biopsies and bronchoalveolar lavage. We also emphasize the importance of multidisciplinary discussion and the complex differential diagnosis.

[Update in interstitial lung disease 2021]

The significant scientific advances about interstitial lung disease from November 2020 to October 2021 which were published in the Chinese and international journals were systematically reviewed in this paper. The year 2021 brought advances in our understanding of the real-world adoption of the antifibrotic medications pirfenidone and nintedanib for US idiopathic pulmonary fibrosis patients, the European statement on the diagnosis and evaluation and treatment of pulmonary fibrosis, the CHEST guideline on the diagnosis and evaluation of hypersensitivity pneumonitis, Chinese expert viewpoints on the progressive fibrosing interstitial lung disease, and international updates on the diagnosis and management of connective tissue disease-associated interstitial lung diseases.

[A CASE OF SUMMER-TYPE HYPERSENSITIVITY PNEUMONITIS DURING IMMUNOSUPPRESSIVE TREATMENT FOR SYSTEMIC SCLEROSIS]

A 70-year-old woman undergoing long-term treatment for systemic scleroderma and secondary Sjögren syndrome developed fever during tapering of steroids. Chest CT showed centrilobular granular shadow and ground glass opacities. The pathology of transbronchial lung biopsy and the findings of bronchoalveolar lavage fluid were consistent with hypersensitivity pneumonitis and positive for anti-Trichosporon asahii antibody. Because her symptoms and imaging findings improved after house cleaning, she was diagnosed with summertype hypersensitivity pneumonitis. When lung lesions are found in patients with collagen disease, it is necessary to distinguish various diseases. In particular, allergic diseases can be difficult to diagnose by steroid therapy. In order to make an accurate diagnosis, medical history and image interpretation should be performed carefully and histologically searched as much as possible.

Occupational Hypersensitivity Pneumonitis in a Japanese Citrus Farmer

Hypersensitivity pneumonitis (HP) sometimes develops in people working in specific environments. We herein report a case of occupation-related HP in a citrus farmer in Japan. A 66-year-old man developed a fever, dyspnea, and general malaise in March after working near a trash dump filled with moldy tangerines. He presented with leukocytosis, bilateral lung opacities on chest radiographs, and intra-alveolar and interstitial lymphocytic inflammation with fibrotic change on a lung biopsy. His symptoms disappeared after admission and recurred on a revisit to the workplace. Fungal culture and a mycobiome analysis using next-generation sequencing suggested an association with exposure to Penicillium digitatum.

Use of peripheral neutrophil to lymphocyte ratio and peripheral monocyte levels to predict survival in fibrotic hypersensitivity pneumonitis (fHP): a multicentre retrospective cohort study

The factors determining disease course and survival in fibrotic hypersensitivity pneumonitis (fHP) have not been fully elucidated.The aim of this study was to describe the characteristics of patients with fHP in a real-world cohort and investigate factors associated with worse outcomes. We aimed to explore the use of neutrophil to lymphocyte ratio (NLR) and peripheral blood monocyte levels in predicting mortality.

METHODS

A retrospective, multicentre, observational UK cohort study.

RESULTS

Patients with fHP were significantly younger than those with idiopathic pulmonary fibrosis (IPF) (median age fHP 73 vs IPF 75 years) and were much more likely to be woman (fHP 61% vs IPF 26%). In almost half of all fHP cases (49%, n=104/211), no causative antigen was identified from either the history or specific antigen testing. Overall, fHP was associated with a better survival than IPF, although median survival of both groups was poor (fHP 62 months vs IPF 52 months).IPF survival in patients with a high NLR was significantly lower than those with a low NLR (44 vs 83 months). A monocyte count ≥0.95 K/uL also predicted significantly poorer outcomes for patients with IPF compared with <0.95 K/uL (33 vs 57 months). In contrast, NLR and monocyte count did not predict survival in the fHP cohort.

CONCLUSIONS

Although fHP has a statistically lower mortality than IPF, absolute survival time of both conditions is poor. High baseline NLR and absolute monocyte counts predict worse survival in IPF but not in fHP, highlighting the potential for divergence in their pathogenic mechanisms.

Lung fibrosis in autoimmune diseases and hypersensitivity: how to separate these from idiopathic pulmonary fibrosis

Lung involvement in autoimmune diseases (AID) is uncommon, but may precede other organ manifestations. A diagnostic problem is chronicity presenting with lung fibrosis. A new category of interstitial pneumonia with autoimmune features for patients with clinical symptoms of AID and presenting with usual interstitial pneumonia (UIP) enables antifibrotic treatment for these patients. Hypersensitivity pneumonia (HP) and other forms of lung fibrosis were not included into this category. As these diseases based on adverse immune reactions often present with unspecific clinical symptoms, a specified pathological diagnosis will assist the clinical evaluation. We aimed to establish etiology-relevant differences of patterns associated with AID or HP combined with lung fibrosis. We retrospectively evaluated 51 cases of AID, and 29 cases of HP with lung fibrosis, and compared these to 24 cases of idiopathic pulmonary fibrosis (UIP/IPF). Subacute AID and HP most often presented with organizing pneumonia (OP), whereas chronicity was associated with UIP. Unspecified fibrosis was seen in a few cases, whereas NSIP pattern was rare. In 9 cases, the underlying etiology could not be defined. Statistically significant features differentiating chronic AID or HP from UIP/IPF are lymphocytic infiltrations into myofibroblastic/fibroblastic foci. Other features significantly associated with AID and HP were granulomas, isolated Langhans giant cells, and protein deposits, but seen in only a minority of cases. A combination of UIP with one of these features enabled a specific etiology-based diagnosis. Besides the antifibrotic drug regimen, additional therapies might be considered.

Development of a Diagnostic Biosensor Method of Hypersensitivity Pneumonitis towards a Point-of-Care Biosensor

In spite of a current increasing trend in the development of miniaturized, standalone point-of-care (PoC) biosensing platforms in the literature, the actual implementation of such systems in the field is far from being a reality although deeply needed. In the particular case of the population screenings for local or regional diseases related to specific pathogens, the diagnosis of the presence of specific antibodies could drastically modify therapies and even the organization of public policies. The aim of this work was to develop a fast, cost-effective detection method based on the manipulation of functionalized magnetic beads for an efficient diagnosis of hypersensitivity pneumonitis (HP), looking for the presence of anti-pigeon antigen antibodies (APAA) in a patient’s serum. We presented a Diagnostic Biosensor Method (DBM) in detail, with validation by comparison with a traditional high-throughput platform (ELISA assay). We also demonstrated that it was compatible with a microfluidic chip that could be eventually incorporated into a PoC for easy and broad deployment using portable optical detectors. After standardization of the different reaction steps, we constructed and validated a plastic chip that could easily be scaled to high-volume manufacturing in the future. The solution proved comparable to conventional ELISA assays traditionally performed by the clinicians in their laboratory and should be compatible with other antibody detection directly from patient samples.

Hypersensitivity pneumonitis in children

INTRODUCTION

Hypersensitivity pneumonitis (HP) is one of the most common forms of interstitial lung disease in children. Due to its common association with occupational environment, it used to be considered an exclusively adult disease; however, hypersensitivity pneumonitis also affects the paediatric population, and is often associated with exposure to antigens in the home environment and with the pastime activities of children.

OBJECTIVE

The aim of the study is to present the current state of knowledge on hypersensitivity pneumonitis in children with a focus on the peculiarities of diagnostic investigation and management of the disease in this age group. The study includes a case report of the disease in a child.

STATE OF KNOWLEDGE

In children, the most common factors causing HP are avian and fungal antigens present in the home environment. Diagnosis is based on the co-occurrence of characteristic clinical presentation, radiographic and pulmonary function tests findings, and a history of exposure to a potential triggering antigen. The main strategy in the management of HP is to eliminate the trigger factor with the use of a systemic corticosteroids therapy in severe or advanced cases.

CONCLUSIONS

Due to the risk of irreversible changes in the respiratory tract, an early diagnosis is very important. A quick identification of the trigger factor and its elimination from the patient's environment makes it possible to apply a less aggressive treatment, and to improve the patient's prognosis. Unfortunately, due to its infrequent occurrence, hypersensitivity pneumonitis is often not taken into account in a differential diagnosis of respiratory diseases in children, which leads to a delayed diagnosis despite the characteristic clinical presentation of the disease.