Use of leflunomide in patients with chronic hypersensitivity pneumonitis

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.

Updates in Hypersensitivity Pneumonitis: A Narrative Review

Purpose of Review

Hypersensitivity pneumonitis (HP) is an immune-mediated disease triggered by a known or unknown antigen. While reversible in the early stages of disease, progression toward irreversible pulmonary fibrosis may occur. This narrative review summarizes recent publications highlighting a methodical approach toward the diagnosis, classification, and management of fibrotic and nonfibrotic HP.

Recent Findings

Establishing the diagnosis of HP is often challenging given its variable clinical course, extensive inciting agents, and overlapping features with other interstitial lung diseases. Recently, HP has been re-classified into nonfibrotic and fibrotic subtypes based on radiographic and histopathological features. Chronic fibrotic HP is associated with significant functional impairment and increased mortality. In addition to antigen avoidance, immunosuppression is the cornerstone of management in nonfibrotic HP. Antifibrotic agents have emerged as a therapeutic option in halting the progression of chronic fibrotic HP.

Summary

The combination of clinical, radiographical, and histopathological data will assist in increasing the diagnostic certainty of HP. The new dichotomization of HP is thought to provide better prognostication for patients. This review provides clinicians with a current and evidence-based approach toward the management of patients with HP.

Challenges in the Diagnosis and Management of Fibrotic Hypersensitivity Pneumonitis: A Practical Review of Current Approaches

Recent advances in fibrotic hypersensitivity pneumonitis include improved diagnostic guidance, systematic assessments of immunosuppressive therapy, and the recent availability of antifibrotic therapy (nintedanib) for those with progressive disease. A standardized approach to diagnosis may lead to better inclusion criteria for future therapeutic protocols and delineation of disease or treatment response predictors for real-world management. This review will highlight current diagnostic and treatment challenges and remaining knowledge gaps or areas of uncertainty, with a practical overview of supporting evidence and its clinical implications. Exposure history, serologic testing for antigen sensitivity, bronchoalveolar lavage lymphocytosis, histopathology, and radiologic findings will be covered in the diagnosis section, with immunosuppression, antifibrotic therapy, lung transplantation, and disease prognosis in the treatment and management section.

Management of Progressive Fibrosing Interstitial Lung Diseases (PF-ILD)

Progressive fibrosing interstitial lung diseases (PF-ILD) consist of a diverse group of interstitial lung diseases (ILD) characterized by a similar clinical phenotype of accelerated respiratory failure, frequent disease exacerbation and earlier mortality. Regardless of underlying disease process, PF-ILD progresses through similar mechanisms of self-sustained dysregulated cell repair, fibroblast proliferation and alveolar dysfunction that can be therapeutically targeted. Antifibrotic therapy with nintedanib or pirfenidone slow lung function decline and are the backbone of treatment for IPF with an expanded indication of PF-ILD for nintedanib. Immunosuppression is utilized for some subtypes of PF-ILD, including connective tissue disease ILD and hypersensitivity pneumonitis. Inhaled treprostinil is a novel therapy that improves exercise tolerance in individuals with PF-ILD and concomitant World Health Organization (WHO) group 3 pulmonary hypertension. Lung transplantation is the only curative therapy and can be considered in an appropriate and interested patient. Supportive care, oxygen therapy when appropriate, and treatment of comorbid conditions are important aspects of PF-ILD management. This review summarizes the current data and recommendations for management of PF-ILD.

Hypersensitivity Pneumonitis: Diagnostic and Therapeutic Challenges

Hypersensitivity pneumonitis (HP) is one of the most common interstitial lung diseases (ILD), that presents unique challenges for a confident diagnosis and limited therapeutic options. The disease is triggered by exposure to a wide variety of inciting antigens in susceptible individuals which results in T-cell hyperactivation and bronchioloalveolar inflammation. However, the genetic risk and the pathogenic mechanisms remain incompletely elucidated. Revised diagnostic criteria have recently been proposed, recommending to classify the disease in fibrotic and non-fibrotic HP which has strong therapeutic and outcome consequences. Confident diagnosis depends on the presence of clinical features of ILD, identification of the antigen(s), typical images on high-resolution computed tomography (HRCT), characteristic histopathological features, and lymphocytosis in the bronchoalveolar lavage. However, identifying the source of antigen is usually challenging, and HRCT and histopathology are often heterogeneous and not typical, supporting the notion that diagnosis should include a multidisciplinary assessment. Antigen removal and treating the inflammatory process is crucial in the progression of the disease since chronic persistent inflammation seems to be one of the mechanisms leading to lung fibrotic remodeling. Fibrotic HP has a few therapeutic options but evidence of efficacy is still scanty. Deciphering the molecular pathobiology of HP will contribute to open new therapeutic avenues and will provide vital insights in the search for novel diagnostic and prognostic biomarkers.

[New developments in the management of hypersensitivity pneumonitis]

INTRODUCTION

Hypersensitivity pneumonitis (HP) is one of the most common interstitial lung diseases, characterized by an inflammatory and/or fibrotic reaction to inhaled antigens.

BACKGROUND

The heterogeneity of presentation and the lack of international guidelines makes management complex. In addition, the current treatment, based on antigen eviction and immunosuppressive drugs, is less effective in the fibrotic forms of HP. This article summarizes the latest data on HP and the new recommendations of the American Thoracic Society (ATS) on the diagnosis of HP.

CONCLUSION

The new ATS recommendations establish a more precise and rigorous diagnostic approach to HP. Multidisciplinary discussion plays a pivotal role both in the diagnosis and the treatment of the disease. Nintedanib has recently been shown to be effective in fibrotic HP.

PERSPECTIVES

Questions remain unanswered about the optimal therapeutic strategy in fibrotic HP, which underlines the need to carry out large-scale studies.