Hypersensitivity pneumonitis
Hypersensitivity Pneumonitis | |
---|---|
Other names | Allergic alveolitis, bagpipe lung, extrinsic allergic alveolitis (EAA) |
Idiopathic Pulmonary Fibrosis, Occupational asthma, Sarcoidosis | |
Prevention | Avoidance of antigen exposure |
Treatment | Avoidance of antigen exposure and sometimes steroids |
Hypersensitivity pneumonitis (HP) or extrinsic allergic alveolitis (EAA) is a syndrome caused by the repetitive inhalation of antigens from the environment in susceptible or sensitized people.[1][2] Common antigens include molds, bacteria, bird droppings, bird feathers, agricultural dusts, bioaerosols and chemicals from paints or plastics.[3] People affected by this type of lung inflammation (pneumonitis) are commonly exposed to the antigens by their occupations, hobbies, the environment and animals.[4][3] The inhaled antigens produce a hypersensitivity immune reaction causing inflammation of the airspaces (alveoli) and small airways (bronchioles) within the lung.[4] Hypersensitivity pneumonitis may eventually lead to interstitial lung disease.[5]
Signs and symptoms
Hypersensitivity pneumonitis (HP) can be categorized as acute, subacute, and chronic based on the duration of the illness.[6][3]
Acute
In the
Subacute
Patients with
. Symptoms are similar to the acute form of the disease, but are less severe and last longer. Findings may be present in patients who have experienced repeated acute attacks.Chronic
In chronic HP, dose of the antigen tends to be low volume but for a longer duration.[2] Patients often lack a history of acute episodes. They have an insidious onset of cough, progressive dyspnea, fatigue, and weight loss. This is associated with partial to complete but gradual reversibility. Avoiding any further exposure is recommended. Clubbing is observed in 50% of patients. Tachypnea, respiratory distress, and inspiratory crackles over lower lung fields often are present.[1] In fact, hypersensitivity pneumonitis can often resemble IPF in terms of pulmonary fibrosis in that many patients experience hypoxemia.[3]
Epidemiology
Although the prevalence of hypersensitivity pneumonitis is not established it is thought to be low.[7] Data collection limitations are a result of difficulty in diagnosis, sub-clinical presentations that go undetected and variability in climate, region and proximity to local industries.[7] The most common types are bird fancier's and farmer's lung.[8][7] Interestingly, cigarette smoking appears to be protective against the disease.[3]
Pathophysiology
Hypersensitivity pneumonitis is caused by an exaggerated
Diagnosis
The diagnosis is made through clinical judgement using a combination of findings because there does not exist a single, universal diagnostic criteria for the disease.[12][3] The diagnosis is most commonly ascertained first with a detailed exposure history followed by a battery of clinical tests including: imaging, histopathology, pulmonary function testing, serology, bronchoscopy, and more.[3][12] In 2020, official guidelines were published by American Thoracic Society, Japanese Respiratory Society, and Asociación Latinoamericana del Tórax which provides a systematic approach to the diagnosis of HP that relies on high-resolution computed tomography.[12]
Exposure History
A detailed occupational, home and environmental exposure history is the first step in diagnosis. Unfortunately, only 60% of inciting antigens are identified in exposure assessment.[12] Re-exposure to the antigen can help aid in diagnosis.[3] Standardized questionnaires have been created to help in obtaining an exposure history although no official questionnaire has been purported.[13] It has been recommended that the questionnaire administered should be relevant to the region in which the exposure has potentially occurred.[14]
Detailed exposure assessments are warranted in the cause of damp indoor environments which have the potential to propagate mold throughout the dwelling. The decision to enlist an
Types
Hypersensitivity pneumonitis may also be called many different names, based on the provoking antigen. These include:
Type[15] | Specific antigen | Exposure |
---|---|---|
Bird fancier's lung Also called bird breeder's lung, pigeon breeder's lung, and poultry worker's lung |
Avian proteins | Feathers and bird droppings [16] |
Bagassosis Exposure to moldy molasses |
Thermophilic actinomycetes[16] | Moldy bagasse (pressed sugarcane) |
Cephalosporium HP | Cephalosporium
|
Contaminated basements (from sewage) |
Cheese-washer's lung | Penicillium casei[16] or P. roqueforti | Cheese casings |
Chemical worker's lung – Isocyanate HP | Methylene bisphenyl isocyanate (MDI)
|
Paints, resins, and polyurethane foams |
Chemical worker's lung[16] – Trimellitic anhydride (TMA) HP | Trimellitic anhydride[16] | Plastics, resins, and paints |
Coffee worker's lung | Coffee bean protein | Coffee bean dust |
Compost lung | Aspergillus | Compost |
Detergent worker's disease | Bacillus subtilis enzymes | Detergent |
Farmer's lung | The molds
The bacteria
|
Moldy hay |
Hot tub lung | Mycobacterium avium complex
|
Mist from hot tubs |
Humidifier lung | The bacteria
The fungi The amoebae |
Mist generated by a machine from standing water |
Japanese summer house HP Also called Japanese summer-type HP | Trichosporon cutaneum
|
Damp wood and mats |
Laboratory worker's lung | Male rat urine protein | Laboratory rats |
Lycoperdonosis | Puffball spores | Spore dust from mature puffballs[17] |
Malt worker's lung | Aspergillus clavatus[16] | Moldy barley |
Maple bark disease | Cryptostroma corticale[16] | Moldy maple bark |
Metalworking fluids HP | Nontuberculous mycobacteria | Mist from metalworking fluids |
Miller's lung | Sitophilus granarius (wheat weevil)[16]
|
Dust-contaminated grain[16] |
Mollusc shell HP | Aquatic animal proteins | Mollusc shell dust |
Mushroom worker's lung | Thermophilic actinomycetes | Mushroom compost |
Peat moss worker's lung | Caused by Penicillium citreonigrum
|
Peat moss |
Pituitary snuff taker's lung | Pituitary snuff | Medication (Diabetes insipidus) |
Sauna worker's lung | Aureobasidium, Graphium spp | Contaminated sauna water |
Sequoiosis | Aureobasidium, Graphium spp | Redwood bark, sawdust |
Streptomyces HP | Streptomyces albus | Contaminated fertilizer |
Suberosis | Penicillium glabrum (formerly known as Penicillium frequentans) | Moldy cork dust |
Tap water HP | Unknown | Contaminated tap water |
Thatched roof disease | Saccharomonospora viridis | Dried grass |
Tobacco worker's lung | Aspergillus spp | Moldy tobacco |
Trombone Player's lung (Brass Player's Lung) | Mycobacterium chelonae
|
Various Mycobacteria inside instruments[18][19] |
Wine-grower's lung | Botrytis cinerea mold | Moldy grapes |
Woodworker's lung | Alternaria, Penicillium spp | Wood pulp, dust |
Of these types, Farmer's Lung and Bird-Breeder's Lung are the most common. "Studies document 8-540 cases per 100,000 persons per year for farmers and 6000-21,000 cases per 100,000 persons per year for pigeon breeders. High attack rates are documented in sporadic outbreaks. Prevalence varies by region, climate, and farming practices. HP affects 0.4–7% of the farming population. Reported prevalence among bird fanciers is estimated to be 20-20,000 cases per 100,000 persons at risk."[1]
Imaging
No single imaging finding is singularly definitive of a diagnosis rather clinicians rely on a constellation of findings. Both chest radiographs and high resolution CT scans can be normal.[1][12]
Chest Radiographs
Acute presentation may reveal poorly defined a micro-nodular interstitial pattern and ground-glass opacities in the lower and mid lung zones. In addition to this, subacute presentations may show reticular nodular opacities in mid-to-lower lung zones.[1] Chronic forms may show fibrotic changes and appear like Idiopathic pulmonary fibrosis.[3]
High-Resolution Computed Tomography
This has become a common diagnostic imaging for the diagnosis and is the modality used in the Official ATS/JRS/ALAT Clinical Practice Guideline.
Histopathology
The acute form can be characterized by poorly formed noncaseating interstitial
Pulmonary Function Testing
Pulmonary function tests (PFTs) can generally reveal a restrictive pattern
Bronchoscopy
Bronchoalveolar lavage (BAL) is a reliable way to detect inflammation in the lung airways. Fluid analysis from the lavage extracted from the airways on bronchoscopy often reveals a total elevation in cell count in addition to an elevation in the percentage of T lymphocytes. This is a good way to help exclude other similar lung diseases like sarcoidosis, infection and Idiopathic pulmonary fibrosis.[8]
Lung biopsy
Lung
When fibrosis develops in chronic hypersensitivity pneumonitis, the differential diagnosis in lung biopsies includes the idiopathic interstitial pneumonias.[23] This group of diseases includes usual interstitial pneumonia, non-specific interstitial pneumonia and cryptogenic organizing pneumonia, among others.[7][22]
The prognosis of some idiopathic interstitial pneumonias, e.g. idiopathic usual interstitial pneumonia (i.e. idiopathic pulmonary fibrosis), are very poor and the treatments of little help. This contrasts the prognosis (and treatment) for hypersensitivity pneumonitis, which is generally fairly good if the allergen is identified and exposures to it significantly reduced or eliminated. Thus, a lung biopsy, in some cases, may make a decisive difference.
Serum Precipitins
Assays for serum IgGs can aid in identifying possible antigenic exposures and are used as markers of exposure [12][10] However, there use is limited in making a definitive diagnosis because serum antibody levels are often elevated in those people who are exposed to an antigen but do not have the disease.[12][3][1] Up to 90% of people exposed to the antigen have precipitins but only 50% of similarly exposed people who are asymptomatic have the same precipitins.[10] False negatives are often common with serum precipitins because of lack of testing reagents for many antigens.[3]
Precipitating IgG antibodies against fungal or avian antigens can be detected in the laboratory using the traditional Ouchterlony immunodiffusion method wherein 'precipitin' lines form on agar plate. However, the time-consuming and labor-intensive precipitin method has largely been replaced by automated IgG antibody tests. These tests can detect IgG antibodies against a variety of potential triggers including Aspergillus fumigatus (Farmer's lung or ABPA) or avian antigens (Bird Fancier's Lung). They are routinely performed on automated immunoassay systems such as ImmunoCAP or IMMULITE.[24][25]
Differential diagnosis
Organic dust toxic syndrome presents similarly with fevers, chills a few hours after exposure to bioaerosols with toxins from fungi, however this is not a true hypersensitivity reaction because it occurs on initial exposure without a preceding sensitization [1]
In chronic disease, HP must be differentiated from very similarly presenting idiopathic pulmonary fibrosis.[12]
Although overlapping in many cases, hypersensitivity pneumonitis may be distinguished from
Similarly, sarcoidosis has noncaseating granuloma formation, however hilar adenopathy is often seen on chest radiographs.[12]
Treatment
The best treatment is to avoid the provoking allergen, as chronic exposure can cause permanent damage and acute disease is often self-limiting. The identification of the provoking antigen and its location must be ascertained by conducting an exposure assessment. Home cleaning is one method of antigen avoidance.
Prognosis
There are few studies examining longitudinal outcomes in patients diagnosed with hypersensitivity pneumonitis. One study in the US showed about a 0.09 to 0.29 per million increase in mortality rates although the cause specific cause was unclear.
Additional images
-
High magnificationTrichrome stain.
See also
References
- ^ a b c d e f g h i j k l "Hypersensitivity Pneumonitis". EMedicine. June 2006.
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- ^ "Hypersensitivity Pneumonitis: Signs and Symptoms". The Regents of The University of California.
- ^ a b c d e Mukhopadhyay, Sanjay. "Pathology of Hypersensitivity Pneumonitis", Retrieved on 3 May 2013.
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- ^ "Sour Note: Sax Can Cause Lung Disease". ABC News. 7 September 2010. Retrieved 4 April 2018.
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- ^ Richardson MD, & Page ID (2017). Aspergillus serology: Have we arrived yet? Medical Mycology, 55(1), 48–55. https://doi.org/10.1093/mmy/myw116
- ^ "Lecture 14: Hypersensitivity". Archived from the original on 2006-02-06. Retrieved 2008-09-18.
- ^ "Allergy & Asthma Disease Management Center: Ask the Expert". Archived from the original on 2007-02-16. Retrieved 2008-09-18.
- ^ "Hypersensitivity Pneumonitis Treatment - Conditions & Treatments - UCSF Medical Center". www.ucsfhealth.org. Retrieved 4 April 2018.