Hypersensitivity pneumonitis
Encyclopedia
Hypersensitivity pneumonitis (also called extrinsic allergic alveolitis, EAA) is an inflammation
of the alveoli within the lung
caused by hypersensitivity
to inhaled organic dusts. Sufferers are commonly exposed to the dust by their occupation or hobbies.
. This leads to an exaggerated immune response (hypersensitivity
). Type III hypersensitivity
and type IV hypersensitivity
occur in hypersensitivity pneumonitis.
, chills, malaise
, cough
, chest tightness, dyspnea
, and headache
. Symptoms resolve within 12 hours to several days upon cessation of exposure.
Acute HP is characterized by poorly formed noncaseating interstitial granuloma
s and mononuclear cell infiltration in a peribronchial distribution with prominent giant cells.
On chest radiographs, a diffuse micronodular interstitial pattern (at times with ground-glass density in the lower and middle lung zones) may be observed. Findings are normal in approximately 10% of patients." In high-resolution CT scans, ground-glass opacities or diffusely increased radiodensities are present. Pulmonary function tests show reduced diffusion capacity of lungs for carbon monoxide (DLCO
). Many patients have hypoxemia at rest, and all patients desaturate with exercise.
, fatigue
, anorexia
, weight loss
, and pleurisy
. Symptoms are similar to the acute form of the disease, but are less severe and last longer. On chest radiographs, micronodular or reticular opacities are most prominent in mid-to-lower lung zones. Findings may be present in patients who have experienced repeated acute attacks.
The subacute, or intermittent, form produces more well-formed noncaseating granulomas, bronchiolitis with or without organizing pneumonia
, and interstitial fibrosis
.
, respiratory distress, and inspiratory crackles over lower lung fields often are present.
On chest radiographs, progressive fibrotic changes with loss of lung volume particularly affect the upper lobes. Nodular or ground-glass opacities are not present. Features of emphysema are found on significant chest films and CT scans.
Chronic forms reveal additional findings of chronic interstitial inflammation and alveolar destruction (honeycombing) associated with dense fibrosis. Cholesterol clefts or asteroid bodies
are present within or outside granulomas.
In addition, many patients have hypoxemia at rest, and all patients desaturate with exercise.
and clinical tests
. A physician may take blood tests, seeking signs of inflammation
, a chest X-ray
and lung function tests. The sufferer shows a restrictive loss of lung function.
Although overlapping in many cases, hypersensitivity pneumonitis may be distinguished from occupational asthma
in that it isn't restricted to only occupational exposure, and that asthma generally is classified as a type I hypersensitivity
. Unlike asthma, hypersensitivity pneumonitis targets lung alveoli rather than bronchi.
, as certain characteristics may suggest the diagnosis.
The differential diagnosis
of hypersensitivity pneumonitis is, primarily, a group of diseases known as idiopathic interstitial pneumonia
s. This group of diseases includes idiopathic pulmonary fibrosis
(IPF) (which manifests histologically as usual interstitial pneumonia
(UIP)), idiopathic non-specific interstitial pneumonia (NSIP) and cryptogenic organizing pneumonia, among others.
Hypersensitivity pneumonitis may manifest, histologically, as usual interstitial pneumonia, i.e. it looks like idiopathic pulmonary fibrosis
under the microscope; however, certain features may suggest it is a hypersensitivity pneumonitis. UIP does not typically have multinucleated giant cells, nor does it typically have a centrilobular distribution; the presence of these features suggest the diagnosis of hypersensitivity pneumonitis.
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.
. These include:
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."
may help to control symptoms but may produce side-effects.
For more information on treatment, please visit UCSF's Hypersensitivity Pneumonitis Treatment page
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
of the alveoli within the lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
caused by hypersensitivity
Hypersensitivity
Hypersensitivity refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity. These reactions may be damaging, uncomfortable, or occasionally fatal. Hypersensitivity reactions require a pre-sensitized state of the host. The four-group classification...
to inhaled organic dusts. Sufferers are commonly exposed to the dust by their occupation or hobbies.
Pathophysiology
Hypersensitivity pneumonitis involves inhalation of an antigenAntigen
An antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...
. This leads to an exaggerated immune response (hypersensitivity
Hypersensitivity
Hypersensitivity refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity. These reactions may be damaging, uncomfortable, or occasionally fatal. Hypersensitivity reactions require a pre-sensitized state of the host. The four-group classification...
). Type III hypersensitivity
Type III hypersensitivity
Type III hypersensitivity occurs when antigens and antibodies are present in roughly equal amounts, causing extensive cross-linking.-Presentation:...
and type IV hypersensitivity
Type IV hypersensitivity
Type IV hypersensitivity is often called delayed type hypersensitivity as the reaction takes two to three days to develop. Unlike the other types, it is not antibody mediated but rather is a type of cell-mediated response....
occur in hypersensitivity pneumonitis.
Symptoms
Hypersensitivity pneumonitis (HP) is categorized as acute, subacute, and chronic based on the duration of the illness. To learn more, please visit UCSF's signs and symptoms page.Acute
In the acute form of HP, symptoms may develop 4–6 hours following heavy exposure to the provoking antigen. Symptoms include feverFever
Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...
, chills, malaise
Malaise
Malaise is a feeling of general discomfort or uneasiness, of being "out of sorts", often the first indication of an infection or other disease. Malaise is often defined in medicinal research as a "general feeling of being unwell"...
, cough
Cough
A cough is a sudden and often repetitively occurring reflex which helps to clear the large breathing passages from secretions, irritants, foreign particles and microbes...
, chest tightness, dyspnea
Dyspnea
Dyspnea , shortness of breath , or air hunger, is the subjective symptom of breathlessness.It is a normal symptom of heavy exertion but becomes pathological if it occurs in unexpected situations...
, and headache
Headache
A headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the...
. Symptoms resolve within 12 hours to several days upon cessation of exposure.
Acute HP is characterized by poorly formed noncaseating interstitial granuloma
Granuloma
Granuloma is a medical term for a tiny collection of immune cells known as macrophages. Granulomas form when the immune system attempts to wall off substances that it perceives as foreign but is unable to eliminate. Such substances include infectious organisms such as bacteria and fungi as well as...
s and mononuclear cell infiltration in a peribronchial distribution with prominent giant cells.
On chest radiographs, a diffuse micronodular interstitial pattern (at times with ground-glass density in the lower and middle lung zones) may be observed. Findings are normal in approximately 10% of patients." In high-resolution CT scans, ground-glass opacities or diffusely increased radiodensities are present. Pulmonary function tests show reduced diffusion capacity of lungs for carbon monoxide (DLCO
DLCO
DLCO is the extent to which oxygen passes from the air sacs of the lungs into the blood. Commonly, it refers to the test used to determine this parameter. It was introduced in 1909....
). Many patients have hypoxemia at rest, and all patients desaturate with exercise.
Subacute
Patients with subacute HP gradually develop a productive cough, dyspneaDyspnea
Dyspnea , shortness of breath , or air hunger, is the subjective symptom of breathlessness.It is a normal symptom of heavy exertion but becomes pathological if it occurs in unexpected situations...
, fatigue
Fatigue (physical)
Fatigue is a state of awareness describing a range of afflictions, usually associated with physical and/or mental weakness, though varying from a general state of lethargy to a specific work-induced burning sensation within one's muscles...
, anorexia
Anorexia (symptom)
Anorexia is the decreased sensation of appetite...
, weight loss
Weight loss
Weight loss, in the context of medicine, health or physical fitness, is a reduction of the total body mass, due to a mean loss of fluid, body fat or adipose tissue and/or lean mass, namely bone mineral deposits, muscle, tendon and other connective tissue...
, and pleurisy
Pleurisy
Pleurisy is an inflammation of the pleura, the lining of the pleural cavity surrounding the lungs. Among other things, infections are the most common cause of pleurisy....
. Symptoms are similar to the acute form of the disease, but are less severe and last longer. On chest radiographs, micronodular or reticular opacities are most prominent in mid-to-lower lung zones. Findings may be present in patients who have experienced repeated acute attacks.
The subacute, or intermittent, form produces more well-formed noncaseating granulomas, bronchiolitis with or without organizing pneumonia
Pneumonia
Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...
, and interstitial fibrosis
Fibrosis
Fibrosis is the formation of excess fibrous connective tissue in an organ or tissue in a reparative or reactive process. This is as opposed to formation of fibrous tissue as a normal constituent of an organ or tissue...
.
Chronic
In chronic HP, 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. TachypneaTachypnea
Tachypnea means rapid breathing. Any rate between 12-20 breaths per minute is normal. Tachypnea is a respiration rate greater than 20 breaths per minute. - Distinction from other breathing terms :...
, respiratory distress, and inspiratory crackles over lower lung fields often are present.
On chest radiographs, progressive fibrotic changes with loss of lung volume particularly affect the upper lobes. Nodular or ground-glass opacities are not present. Features of emphysema are found on significant chest films and CT scans.
Chronic forms reveal additional findings of chronic interstitial inflammation and alveolar destruction (honeycombing) associated with dense fibrosis. Cholesterol clefts or asteroid bodies
Asteroid body
An asteroid body , is a histopathologic finding seen in granulomatous diseases, such as sarcoidosis and foreign body giant cell reactions....
are present within or outside granulomas.
In addition, many patients have hypoxemia at rest, and all patients desaturate with exercise.
Diagnosis
The diagnosis is based upon a history of symptoms after exposure to the allergenAllergen
An allergen is any substance that can cause an allergy. In technical terms, an allergen is a non-parasitic antigen capable of stimulating a type-I hypersensitivity reaction in atopic individuals....
and clinical tests
Clinical research
Clinical research is a branch of medical science that determines the safety and effectiveness of medications, devices, diagnostic products and treatment regimens intended for human use...
. A physician may take blood tests, seeking signs of inflammation
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
, a chest X-ray
Chest X-ray
In medicine, a chest radiograph, commonly called a chest X-ray , is a projection radiograph of the chest used to diagnose conditions affecting the chest, its contents, and nearby structures...
and lung function tests. The sufferer shows a restrictive loss of lung function.
Although overlapping in many cases, hypersensitivity pneumonitis may be distinguished from occupational asthma
Occupational asthma
Occupational asthma is an occupational condition defined as: "a disease characterized by variable airflow limitation and/or airway hyper-responsiveness due to causes and conditions attributable to a particular occupational environment and not stimuli encountered outside the workplace".Asthma is...
in that it isn't restricted to only occupational exposure, and that asthma generally is classified as a type I hypersensitivity
Type I hypersensitivity
Type I hypersensitivity is an allergic reaction provoked by reexposure to a specific type of antigen referred to as an allergen, or to a nonimmunologic stimulus like cold weather or exercise...
. Unlike asthma, hypersensitivity pneumonitis targets lung alveoli rather than bronchi.
Lung biopsy
Lung biopsies are rarely diagnostic, but may help intensify the search for an allergenAllergen
An allergen is any substance that can cause an allergy. In technical terms, an allergen is a non-parasitic antigen capable of stimulating a type-I hypersensitivity reaction in atopic individuals....
, as certain characteristics may suggest the diagnosis.
The differential diagnosis
Differential diagnosis
A differential diagnosis is a systematic diagnostic method used to identify the presence of an entity where multiple alternatives are possible , and may also refer to any of the included candidate alternatives A differential diagnosis (sometimes abbreviated DDx, ddx, DD, D/Dx, or ΔΔ) is a...
of hypersensitivity pneumonitis is, primarily, a group of diseases known as idiopathic interstitial pneumonia
Idiopathic interstitial pneumonia
Idiopathic interstitial pneumonia , or noninfectious pneumoniaare a class of diffuse lung diseases. Is a term used for a type of diffuse parenchymal lung disease , also called interstitial lung disease .There are seven distinct subtypes of IIP.-Histologic classification:Classification can be...
s. This group of diseases includes idiopathic pulmonary fibrosis
Idiopathic pulmonary fibrosis
Idiopathic pulmonary fibrosis is a chronic, progressive form of lung disease characterized by fibrosis of the supporting framework of the lungs...
(IPF) (which manifests histologically as usual interstitial pneumonia
Usual interstitial pneumonia
Usual interstitial pneumonia is a form of lung disease characterized by progressive scarring of both lungs. The scarring involves the supporting framework of the lung. UIP is thus classified as a form of interstitial lung disease. The term "usual" refers to the fact that UIP is the most common...
(UIP)), idiopathic non-specific interstitial pneumonia (NSIP) and cryptogenic organizing pneumonia, among others.
Hypersensitivity pneumonitis may manifest, histologically, as usual interstitial pneumonia, i.e. it looks like idiopathic pulmonary fibrosis
Idiopathic pulmonary fibrosis
Idiopathic pulmonary fibrosis is a chronic, progressive form of lung disease characterized by fibrosis of the supporting framework of the lungs...
under the microscope; however, certain features may suggest it is a hypersensitivity pneumonitis. UIP does not typically have multinucleated giant cells, nor does it typically have a centrilobular distribution; the presence of these features suggest the diagnosis of hypersensitivity pneumonitis.
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.
Types
Hypersensitivity Pneumonitis (HP) may also be called many different names, based on the provoking antigenAntigen
An antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...
. These include:
| Type | Specific antigen | Exposure |
|---|---|---|
| Bird fancier's lung Bird fancier's lung Bird fancier's lung is a type of hypersensitivity pneumonitis caused by bird droppings. The lungs become inflamed with granuloma formation.Bird Fancier's Lung , also called bird-breeder's lung and pigeon-breeder's lung, is a subset of Hypersensitivity pneumonitis... Also called bird breeder's lung, pigeon breeder's lung, and poultry worker's Lung. |
Avian proteins | Feathers and bird droppings |
| Farmer's lung Farmer's lung Farmer's lung is a hypersensitivity pneumonitis induced by the inhalation of biologic dusts coming from hay dust or mould spores or other agricultural products. It results in a type III hypersensitivity inflammatory response and can progress to become a chronic condition which is considered... |
The mold Mold Molds are fungi that grow in the form of multicellular filaments called hyphae. Molds are not considered to be microbes but microscopic fungi that grow as single cells called yeasts... s
|
Moldy hay |
| Crack lung | Crack cocaine Crack cocaine Crack cocaine is the freebase form of cocaine that can be smoked. It may also be termed rock, hard, iron, cavvy, base, or just crack; it is the most addictive form of cocaine. Crack rocks offer a short but intense high to smokers... |
Heavy crack smoking |
| Bagassosis | Thermophilic actinomycetes | Moldy bagasse (pressed sugarcane) |
| Lycoperdonosis Lycoperdonosis Lycoperdonosis is a respiratory disease caused by the inhalation of large quantities of spores from mature puffballs. It is classified as a hypersensitivity pneumonitis —an inflammation of the alveoli within the lung caused by hypersensitivity to inhaled organic dusts... |
Puffball Puffball A puffball is a member of any of several groups of fungus in the division Basidiomycota. The puffballs were previously treated as a taxonomic group called the Gasteromycetes or Gasteromycetidae, but they are now known to be a polyphyletic assemblage. The distinguishing feature of all puffballs is... spores |
Spore dust from mature puffballs |
| Malt worker's lung | Aspergillus clavatus | Moldy barley Barley Barley is a major cereal grain, a member of the grass family. It serves as a major animal fodder, as a base malt for beer and certain distilled beverages, and as a component of various health foods... |
| Maple bark disease | Cryptostroma corticale | Moldy maple Maple Acer is a genus of trees or shrubs commonly known as maple.Maples are variously classified in a family of their own, the Aceraceae, or together with the Hippocastanaceae included in the family Sapindaceae. Modern classifications, including the Angiosperm Phylogeny Group system, favour inclusion in... bark |
| Miller's lung | Sitophilus granarius (wheat weevil) | Dust-contaminated grain |
| Penguin Humidifier lung | The bacteria
the fungi
and the amoebae
|
Mist generated by a machine from standing water |
| Mushroom worker's lung | Thermophilic actinomycetes | Mushroom compost |
| Compost lung | Aspergillus Aspergillus Aspergillus is a genus consisting of several hundred mold species found in various climates worldwide. Aspergillus was first catalogued in 1729 by the Italian priest and biologist Pier Antonio Micheli... |
Compost Compost Compost is organic matter that has been decomposed and recycled as a fertilizer and soil amendment. Compost is a key ingredient in organic farming. At its most essential, the process of composting requires simply piling up waste outdoors and waiting for the materials to break down from anywhere... |
| Peat moss worker's lung | Caused by Monocillium sp. and Penicillium citreonigrum | Peat moss |
| Suberosis | Penicillum frequentans | Moldy cork dust |
| Japanese summer house HP | Trichosporon cutaneum | Damp wood and mats Tatami A is a type of mat used as a flooring material in traditional Japanese-style rooms. Traditionally made of rice straw to form the core , with a covering of woven soft rush straw, tatami are made in standard sizes, with the length exactly twice the width... |
| Cheese-washer's lung | Penicillum casei or P.roqueforti | Cheese casings |
| Metalworking fluids HP | Nontuberculous Mycobacteria. | Mist from metalworking fluids. |
| Hot tub lung | Mycobacterium avium complex | Mist from hot tub Hot tub A hot tub is a large tub or small pool full of heated water and used for soaking, relaxation, massage, or hydrotherapy. In most cases, they have jets for massage purposes. Hot tubs are usually located outdoors, and are often sheltered for protection from the elements, as well as for privacy.... s. |
| Mollusc shell HP | Aquatic animal proteins | Mollusc shell dust. |
| Isocyanate HP | TDI, HDI, and MDI | Paints, resins, and polyurethane foams. |
| TMA HP chemical worker's lung |
Trimellitic anhydride | Plastics, resins, and paints. |
| Berylliosis Berylliosis Berylliosis, or chronic beryllium disease , is a chronic allergic-type lung response and chronic lung disease caused by exposure to beryllium and its compounds. As an occupational lung disease, it is most classically associated with beryllium mining or manufacturing of fluorescent light bulbs... |
Beryllium Beryllium Beryllium is the chemical element with the symbol Be and atomic number 4. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl and chrysoberyl... |
Electronics industry |
| Wine-grower's lung | Botrytis cinerea mold | Moldy grapes |
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."
Treatment
The best treatment is to avoid the provoking allergen, as chronic exposure can cause permanent damage. Corticosteroids such as PrednisolonePrednisolone
Prednisolone is the active metabolite of prednisone, which is also used as a drug.-Uses:Prednisolone is a corticosteroid drug with predominant glucocorticoid and low mineralocorticoid activity, making it useful for the treatment of a wide range of inflammatory and auto-immune conditions such as...
may help to control symptoms but may produce side-effects.
For more information on treatment, please visit UCSF's Hypersensitivity Pneumonitis Treatment page