Paula Irina BARATA1*
“Vasile Goldiș”
Western University of Arad, Arad, Romania1
*For Correspondence
barata_paula@yahoo.com
Publication Date: June 16, 2025Hypersensitivity pneumonitis
(HP), also known as extrinsic allergic alveolitis, is an interstitial lung
disease triggered by repeated inhalation of environmental antigens in
genetically predisposed individuals. These antigens—ranging from microbial
agents, animal proteins, and agricultural dust to chemical compounds—elicit a
complex immune response that may progress from reversible inflammation to
irreversible fibrosis. HP presents a broad clinical spectrum, from acute,
self-limiting episodes to chronic, progressive fibrosing disease that can mimic
other interstitial lung disorders, such as idiopathic pulmonary fibrosis.
The pathogenesis involves both
type III (immune complex–mediated) and type IV (T-cell–mediated)
hypersensitivity reactions, leading to alveolar and small airway inflammation,
granuloma formation, and, in some cases, architectural remodeling and fibrosis.
Genetic susceptibility, such as certain HLA haplotypes and telomere-related
mutations, has been associated with disease development and progression.
Accurate diagnosis remains challenging due to the nonspecific nature of
symptoms—dyspnea, cough, fatigue—and the variability in radiologic and
histopathologic findings. Diagnosis relies on a multidisciplinary approach
integrating clinical context, high-resolution computed tomography (HRCT),
pulmonary function tests, bronchoalveolar lavage, and sometimes lung biopsy.
Identification and avoidance of the inciting antigen are critical and often
determine long-term prognosis.
Therapeutic strategies vary
depending on disease stage. Antigen avoidance is the cornerstone of treatment
and can reverse early inflammation. In more advanced or fibrotic forms,
systemic corticosteroids and immunosuppressive agents such as azathioprine or
mycophenolate mofetil are commonly used. Recently, antifibrotic therapy with
nintedanib has shown efficacy in slowing disease progression in chronic
fibrosing HP. Lung transplantation remains an option for patients with
advanced, treatment-refractory disease.
This chapter provides a
comprehensive overview of hypersensitivity pneumonitis, emphasizing current
understanding of its immunopathogenesis, the diagnostic challenges it poses,
and evolving approaches to management, including the role of antifibrotic therapy
and transplantation.
Keywords
Hypersensitivity Pneumonitis, Interstitial Lung Disease, Antigen Avoidance, Fibrosis, Immunosuppressive Therapy
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