hypersensitivity pneumonitis; extrinsic allergic alveolitis; pigeon breeder's lung; bird fancier's lung; farmer's lung; allergic pneumonitis
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Etiology
- type-1 hypersensitivity reaction to repeated inhalation of finely dispersed extrinsic antigen[3]
- fungal precipitins (mold)
- exposure to flooded basement
- thermophilic actinomycetes
- avian proteins, bird droppings (pigeon breeder's lung)
- animal dander, animal proteins
- chemicals, including agricultural dust
- bacteria
Epidemiology
- prevalence in North America unknown
- prevalence in high-risk population is 7-21%
- office workers exposed thermophilic bacteria
- pigeon breeders
- farmers, diary farmers (farmer's lung)
Pathology
- biopsy shows patch infiltration of alveolar walls with lymphocytes, plasma cells, macrophages & neutrophils
- loosely-formed, non-caseating granuloma
- may lead to irreversible interstitial fibrosis (restrictive lung disease)
- early disease is generally reversible if offending agent is removed
- type-4 hypersensitivity: cell mediated
Clinical manifestations
- acute or classic form
- subacute form
- can develop after weeks of continuous inhalation of antigen
- low grade fever
- weight loss
- cough
- wheezing
- progressive dyspnea
- chronic form
- may result from chronic exposure to low levels of antigen
- may present insidiously
- dyspnea on exertion
- chronic cough
- absence of systemic symptoms
- irreversible lung fibrosis may occur prior to presentation or diagnosis
Laboratory
- flow cytometry of bronchoalveolar lavage specimen:
- CD4/CD8 ratio < 1.0 suggestive of hypersensitivity pneumonitis[8]
- precipitating antibodies to eliciting antigen are present in serum demonstrated by gel diffusion
- precipitating IgG to eliciting antigen indicate prior exposure but active disease
- in chronic form causative antigen may not be identified[3]
- see ARUP consult[4]
- apparently a Loinc for hypersensitivity pneumonitis panel
Diagnostic procedures
- pulmonary function testing:
- restrictive lung disease pattern occurs early
- hypoxia
- diminished FEV1, FVC & DLCO
- pre- post-bronchodilator testing
- bronchioalveolar lavage
- predominance of lymphocytes (70%)
- > 40% CD8 cells
- these findings also occur in asymptomatic exposed individuals
- lung biopsy is rarely required
- air sampling if suspicion for airborne allergen is high, but interpretation of relevance to patient is difficult
- skin testing for environmental antigens are said to be non-specific
Radiology
- chest X-ray:
- patchy or diffuse infiltrates or micronodules
- bilateral nodular opacities
- may be normal early in the disease
- computed tomography (thorax)
- can identify early interstitial changes
- centrolobular micronodules, middle & upper lobe predominance
- septal lung thickening with traction bronchiectasis, middle & upper lobe predominance
- ground glass opacities
- absence of honeycombing
- interstitial pneumonia pattern may be seen
Differential diagnosis
- other forms of granulomatous disease
- vasculitis: Wegener's granulomatosis
- idiopathic pulmonary fibrosis
- berylliosis
- humidifier fever
* symptoms appearing 4-12 hours after exposure to mold make these other disorders unlikely
Management
- removal of exposure to & avoidance of causative agent
- resolution of symptoms in 48 hours
- diagnostic & therapeutic (action of choice)
- corticosteroids (high dose)
- often used for patients with more severe symptoms &/or with evidence of fibrosis[3]
- little effect on the natural course of the disease
- prednisone maximum of 60 mg daily tapered slowly over several weeks[7]
More general terms
More specific terms
- acute hypersensitivity pneumonitis
- bagassosis
- chronic hypersensitivity pneumonitis
- humidifier lung disease
- suberosis; corkhandler disease; corkworker lung
Additional terms
References
- ↑ Stedman's Medical Dictionary 26th ed, Williams & Wilkins, Baltimore, 1995
- ↑ Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed) Lippincott-Raven, Philadelphia, 1998, pg 759-60
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Medical Knowledge Self Assessment Program (MKSAP) 11, 14, 15, 16, 17, 18, 19. American College of Physicians, Philadelphia 1998, 2006, 2009, 2012, 2015, 2018, 2022.
Medical Knowledge Self Assessment Program (MKSAP) 19 Board Basics. An Enhancement to MKSAP19. American College of Physicians, Philadelphia 2022 - ↑ 4.0 4.1 ARUP Consult: Hypersensitivity Pneumonitis - Extrinsic Allergic Alveolitis The Physician's Guide to Laboratory Test Selection & Interpretation https://www.arupconsult.com/content/hypersensitivity-pneumonitis
- ↑ Lacasse Y, Girard M, Cormier Y. Recent advances in hypersensitivity pneumonitis. Chest. 2012 Jul;142(1):208-17. Review. PMID: https://www.ncbi.nlm.nih.gov/pubmed/22796841
- ↑ Vasakova M, Morell F, Walsh S, Leslie K, Raghu G. Hypersensitivity Pneumonitis: Perspectives in Diagnosis and Management. Am J Respir Crit Care Med. 2017 Sep 15;196(6):680-689. PMID: https://www.ncbi.nlm.nih.gov/pubmed/28598197
- ↑ 7.0 7.1 NEJM Knowledge Plus Question of the Week. April 6, 2021 https://knowledgeplus.nejm.org/question-of-week/270/
Selman M, Buendia-Roldan I. Immunopathology, diagnosis, and management of hypersensitivity pneumonitis. Semin Respir Crit Care Med 2012 Sep 25; 33:543 PMID: https://www.ncbi.nlm.nih.gov/pubmed/23001807
Riario Sforza GG, Marinou A. Hypersensitivity pneumonitis: a complex lung disease. Clin Mol Allergy 2017; 15:6. PMID: https://www.ncbi.nlm.nih.gov/pubmed/28286422 PMCID: PMC5339989 Free PMC article - ↑ 8.0 8.1 NEJM Knowledge+ Allergy/Immunology
- ↑ Greenberger PA. Hypersensitivity pneumonitis: A fibrosing alveolitis produced by inhalation of diverse antigens. J Allergy Clin Immunol. 2019 Apr;143(4):1295-1301. PMID: https://www.ncbi.nlm.nih.gov/pubmed/30448501 Review.
- ↑ No authors listed Hypersensitivity pneumonitis Nat Rev Dis Primers. 2020 Aug 6;6(1):66. PMID: https://www.ncbi.nlm.nih.gov/pubmed/32764556