Abstract
The diagnosis of hypersensitivity pneumonitis (HP) relies on the clinical evaluation of a number of features, including a history of significant exposure to potentially causative antigens, physical examination, chest CT scan appearances, bronchoalveolar lavage lymphocytosis, and, in selected cases, histology. The presence of fibrosis is associated with higher morbidity and mortality. Differentiating fibrotic HP from the idiopathic interstitial pneumonias can be a challenge. Furthermore, even in the context of a clear diagnosis of fibrotic HP, the disease behaviour can parallel that of idiopathic pulmonary fibrosis in a subgroup, with inexorable progression despite treatment. We review the current knowledge on the diagnosis, management, and prognosis of HP with particular focus on the fibrotic phenotype.
Highlights
Hypersensitivity pneumonitis (HP), known as extrinsic allergic alveolitis, is a clinical syndrome characterized by variable presentations
The diagnosis of fibrotic HP relies on the integration of: (a) non-specific symptoms, such as dyspnea and cough, as well as fatigue and malaise, that develop in a specific environment, (b) compatible chest computer tomography (CT) scan features, (c) detection of serum antibodies against suspected antigens, (d) lymphocytosis on bronchoalveolar lavage (BAL), and/or (e) identification of a granulomatous bronchiolocentric interstitial pneumonitis on adequate lung biopsies
A number of randomized placebo-controlled trials are currently recruiting in non-idiopathic pulmonary fibrosis (IPF) progressive fibrosis patient groups, including a trial evaluating the effects of pirfenidone as an add-on drug to background immunosuppressive treatment in patients with fibrotic HP [65], and a study is evaluating the effects of nintedanib compared to placebo in a wider group of patients with non-IPF progressive fibrotic lung disease, including fibrotic HP [66]
Summary
Hypersensitivity pneumonitis (HP), known as extrinsic allergic alveolitis, is a clinical syndrome characterized by variable presentations (acute, subacute, and chronic/fibrotic). Two major attempts to reach an agreement on a definition by groups of international experts failed to provide a widely accepted and validated diagnostic approach [1,4]. In this context, symptoms, radiographic and histopathological findings in patients with fibrotic. In HP, the presence of fibrosis histologically or on chest computer tomography (CT) is associated with a decreased survival In view of this and of the diagnostic difficulties in separating fibrotic. HP from IPF or other interstitial lung diseases (ILDs) in a proportion of patients, this review article focuses on fibrotic HP with particular attention to current knowledge on the diagnosis, management, and prognosis of this form of the disease. For the purpose of this review we will use the term fibrotic HP rather than chronic HP, as there can be patients with a chronic subacute form without significant fibrosis visible on CT
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