Hypersensitivity pneumonitis overview

Hypersensitivity pneumonitis Microchapters

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Overview

Historical Perspective

Classification

Pathophysiology

Causes

Differentiating Hypersensitivity pneumonitis from other Diseases

Epidemiology and Demographics

Risk Factors

Screening

Natural History, Complications & Prognosis

Diagnosis

Diagnostic Criteria

History and Symptoms

Physical Examination

Laboratory Findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

## Overview

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Hypersensitivity pneumonitis (HP), also called extrinsic allergic alveolitis (EAA), is not a single disease but is a complex syndrome of varying intensity, clinical presentation, and natural history.

The syndrome was first described in Iceland in 1874 and termed heykatarr. The syndrome is caused by sensitization to repeated inhalation of dusts containing one of 300 organic antigens. These organic dusts come from a wide variety of sources but most commonly include:

* Dairy and grain products
* Animal dander and protein
* Wood bark
* Water reservoir vaporizers

The two most common antigens are:

1. Thermophilic actinomycetes and
2. Avian proteins

As a rseult of exposure to thee antigens, the two most common causes (i.e. diseases) are:

1. Farmer's lung and
2. Bird fancier's lung

Pathologically, the HP syndrome is associated with diffuse inflammation of lung parenchyma and airways.

Based on the length and intensity of exposure and subsequent duration of illness, there are 3 clinical presentations of HP:

1. Acute
2. Subacute (intermittent)
3. Chronic progressive

Synonyms and related keywords: hypersensitivity pneumonitis, HP, bird fancier's lung, extrinsic allergic alveolitis, farmer's lung, Saccharopolyspora rectivirgula, S rectivirgula, Micropolyspora faeni, M faeni, Thermoactinomyces sacchari, T sacchari, Thermoactinomyces vulgaris, T vulgaris, Penicillium casei, P casei, Aspergillus clavatus, A clavatus, Mucor stolonifer, M stolonifer, Sitophilus granarius, S granarius, Cladosporium, heykatarr, bagassosis, grain handler's lung, humidifier lung, air-conditioner lung, bird breeder's lung, cheese worker's lung, malt worker's lung,paprika splitter's lung, mollusk shell hypersensitivity, chemical worker's lung, pulmonary disease, lung disease.

## Historical Perspective

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* [Disease name] was first discovered by [scientist name], a [nationality + occupation], in [year] during/following [event].
* In [year], [gene] mutations were first identified in the pathogenesis of [disease name].
* In [year], the first [discovery] was developed by [scientist] to treat/diagnose [disease name].

## Classification

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* [Disease name] may be classified according to [classification method] into [number] subtypes/groups:

* [group1]
* [group2]
* [group3]

* Other variants of [disease name] include [disease subtype 1], [disease subtype 2], and [disease subtype 3].

## Pathophysiology

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* The pathogenesis of [disease name] is characterized by [feature1], [feature2], and [feature3].
* The [gene name] gene/Mutation in [gene name] has been associated with the development of [disease name], involving the [molecular pathway] pathway.
* On gross pathology, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].
* On microscopic histopathological analysis, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].

## Causes

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* [Disease name] may be caused by either [cause1], [cause2], or [cause3].
* [Disease name] is caused by a mutation in the [gene1], [gene2], or [gene3] gene[s].
* There are no established causes for [disease name].

## Differentiating [disease name] from other Diseases

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* [Disease name] must be differentiated from other diseases that cause [clinical feature 1], [clinical feature 2], and [clinical feature 3], such as:

* [Differential dx1]
* [Differential dx2]
* [Differential dx3]

## Epidemiology and Demographics

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* The prevalence of [disease name] is approximately [number or range] per 100,000 individuals worldwide.
* In [year], the incidence of [disease name] was estimated to be [number or range] cases per 100,000 individuals in [location].

### Age

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* Patients of all age groups may develop [disease name].

* [Disease name] is more commonly observed among patients aged [age range] years old.
* [Disease name] is more commonly observed among [elderly patients/young patients/children].

### Gender

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* [Disease name] affects men and women equally.

* [Gender 1] are more commonly affected with [disease name] than [gender 2].
* The [gender 1] to [Gender 2] ratio is approximately [number > 1] to 1.

### Race

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* There is no racial predilection for [disease name].

* [Disease name] usually affects individuals of the [race 1] race.
* [Race 2] individuals are less likely to develop [disease name].

## Risk Factors

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* Common risk factors in the development of [disease name] are [risk factor 1], [risk factor 2], [risk factor 3], and [risk factor 4].

## Natural History, Complications and Prognosis

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* The majority of patients with [disease name] remain asymptomatic for [duration/years].
* Early clinical features include [manifestation 1], [manifestation 2], and [manifestation 3].
* If left untreated, [#%] of patients with [disease name] may progress to develop [manifestation 1], [manifestation 2], and [manifestation 3].
* Common complications of [disease name] include [complication 1], [complication 2], and [complication 3].
* Prognosis is generally [excellent/good/poor], and the [1/5/10­year mortality/survival rate] of patients with [disease name] is approximately [#%].

## Diagnosis

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### Diagnostic Criteria

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* The diagnosis of [disease name] is made when at least [number] of the following [number] diagnostic criteria are met:

* [criterion 1]
* [criterion 2]
* [criterion 3]
* [criterion 4]

### Symptoms

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* [Disease name] is usually asymptomatic.
* Symptoms of [disease name] may include the following:

* [symptom 1]
* [symptom 2]
* [symptom 3]
* [symptom 4]
* [symptom 5]
* [symptom 6]

### Physical Examination

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* Patients with [disease name] usually appear [general appearance].
* Physical examination may be remarkable for:

* [finding 1]
* [finding 2]
* [finding 3]
* [finding 4]
* [finding 5]
* [finding 6]

### Laboratory Findings

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* There are no specific laboratory findings associated with [disease name].

* A [positive/negative] [test name] is diagnostic of [disease name].
* An [elevated/reduced] concentration of [serum/blood/urinary/CSF/other] [lab test] is diagnostic of [disease name].
* Other laboratory findings consistent with the diagnosis of [disease name] include [abnormal test 1], [abnormal test 2], and [abnormal test 3].

### Imaging Findings

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* There are no [imaging study] findings associated with [disease name].

* [Imaging study 1] is the imaging modality of choice for [disease name].
* On [imaging study 1], [disease name] is characterized by [finding 1], [finding 2], and [finding 3].
* [Imaging study 2] may demonstrate [finding 1], [finding 2], and [finding 3].

### Other Diagnostic Studies

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* [Disease name] may also be diagnosed using [diagnostic study name].
* Findings on [diagnostic study name] include [finding 1], [finding 2], and [finding 3].

## Treatment

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### Medical Therapy

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* There is no treatment for [disease name]; the mainstay of therapy is supportive care.

* The mainstay of therapy for [disease name] is [medical therapy 1] and [medical therapy 2].
* [Medical therapy 1] acts by [mechanism of action 1].
* Response to [medical therapy 1] can be monitored with [test/physical finding/imaging] every [frequency/duration].

### Surgery

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* Surgery is the mainstay of therapy for [disease name].
* [Surgical procedure] in conjunction with [chemotherapy/radiation] is the most common approach to the treatment of [disease name].
* [Surgical procedure] can only be performed for patients with [disease stage] [disease name].

### Prevention

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* There are no primary preventive measures available for [disease name].

* Effective measures for the primary prevention of [disease name] include [measure1], [measure2], and [measure3].

* Once diagnosed and successfully treated, patients with [disease name] are followed-up every [duration]. Follow-up testing includes [test 1], [test 2], and [test 3].

## References

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Template:Respiratory pathology

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