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Chapter 19: Hypersensitivity pneumonitis

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Hypersensitivity pneumonitis (HP), also referred to as extrinsic allergic alveolitis, is characterized by non-IgE‐mediated inflammation of the parenchyma, alveoli, and terminal airways of the lung initiated by inhaled antigens in a susceptible host. Etiologic agents of HP are either organic high molecular weight compounds such as bacteria, fungi, amoebae, plant, and animal proteins or inorganic low molecular weight haptens such as isocyanate and drugs including amiodarone, nitrofurantoin, and minocycline. Six significant predictors have been identified that provide ∼95% diagnostic accuracy. These six predictors are (1) exposure to a known offending allergen, (2) positive precipitating antibodies to the offending antigen, (3) recurrent episodes of symptoms, (4) inspiratory crackles on lung auscultation, (5) symptoms occurring 4‐8 hours after exposure, and (6) weight loss. HP is staged into acute, subacute, and chronic. In the acute stage after direct exposure to the antigen, there is fever, chills, nonproductive cough, dyspnea, malaise, and myalgias, all resembling influenza. However, if obtained, a chest radiograph shows nodular infiltrates, and pulmonary function testing is restrictive (unless the cause is avian in which obstruction or obstruction with restriction is present). In the chronic stage, fever and chills are absent, but weight loss can occur. The immunologic response includes activated macrophages and CD8+ cytotoxic lymphocytes, and bronchoalveolar lavage fluid reveals marked lymphocytosis with a ratio of CD4+ cells to CD8+ cells <1. Activated macrophages have increased expression of CD80/CD86, and T cells have increased expression of its counter-ligand CD28, evidence for heightened antigen presentation.
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Keywords: Acute stage; chronic stage; extrinsic allergic alveolitis; hypersensitivity pneumonitis; inorganic low molecular weight haptens; isocyanate; nodular infiltrates; organic high molecular weight compounds; precipitating antibodies; pulmonary function; testing i

Document Type: Research Article

Publication date: 01 May 2012

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  • Allergy and Asthma Proceedings is a peer reviewed publication dedicated to distributing timely scientific research regarding advancements in the knowledge and practice of allergy, asthma and immunology. Its primary readership consists of allergists and pulmonologists.

    The goal of the Proceedings is to publish articles with a predominantly clinical focus which directly impact quality of care for patients with allergic disease and asthma.

    Featured topics include asthma, rhinitis, sinusitis, food allergies, allergic skin diseases, diagnostic techniques, allergens, and treatment modalities. Published material includes peer-reviewed original research, clinical trials and review articles.

    Articles marked "F" offer free full text for personal noncommercial use only.

    The journal is indexed in Thomson Reuters Web of Science and Science Citation Index Expanded, plus the National Library of Medicine's PubMed service.
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