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Hypersensitivity pneumonitis

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Related Terms
  • A. clavatus,air conditioner lung, Aspergillus clavatus,alveolitis, bagassosis, bird breeder's lung, bird fancier's lung, cheese worker's lung, chemical worker's lung, Cladosporium,coffee-worker's lung, detergent-worker's lung, epoxy-resin lung, extrinsic allergic alveolitis, farmer's lung, farm-worker's lung, grain handler's lung, HP, humidifier lung, hypersensitivity pneumonitides, laboratory-worker's lung, lifeguard lung, lung disease, lung inflammation, M. faeni, M. stolonifer,malt worker's lung, Micropolyspora faeni,miller's lung, mollusk shell hypersensitivity, Mucor stolonifer, mushroom picker's disease, occupational disease, P. casei,paprika splitter's lung, Penicillium casei,pneumonia, pneumonitides, pneumonitis, poultry-worker's lung, pulmonary disease, pulmonary fibrosis, S. granarius, S. rectivirgula, Saccharopolyspora rectivirgula, Sitophilus granarius, T. sacchari, T. vulgaris, Thermoactinomyces sacchari, Thermoactinomyces vulgaris,winemaker's lung, woodworker's lung.

Background
  • Pneumonitis is a general term for inflammation of lung tissue.
  • Hypersensitivity pneumonitis (also called allergic alveolitis) is an inflammation in the lungs caused by exposure to an allergen, usually organic dust (like fungus spores from moldy hay or bird droppings). Since these allergens are common in certain lines of work (farming, for example), hypersensitivity pneumonitis is usually considered an occupational disease.
  • When a person inhales such allergens the first time, no symptoms appear. After repeated exposure to the allergen, the immune system of an allergic person becomes sensitized. Once sensitized, the immune system can quickly detect the allergen when it enters the body and produce antibodies called immunoglobulin E (IgE) to fight off the allergen. These antibodies trigger the release of chemical mediators, which cause allergy symptoms, such as hives, rash, teary eyes and runny nose.
  • Acute hypersensitivity pneumonitis may occur in sensitized individuals four to six hours after exposure to the allergen. The alveoli (tiny air sacs in the lung) become inflamed, and their walls fill up with white blood cells. In some cases, the sacs will fill with fluid. Chronic illness may develop after frequent exposure of high concentrations of the allergen. If the disease is chronic and recurs as a result of continued allergen exposure, parts of the lung may develop fibrous scar tissue (also known as pulmonary fibrosis) and may no longer function normally. At this point, the damage is usually irreversible.
  • The prevalence of hypersensitivity pneumonitis depends on the region, climate and farming practices. In the United States, it was estimated in 2003 that the disease affects 0.4-7% of the farming population. In the United Kingdom, it was estimated in 2003 there are between 420-3,000 cases of farmer's lung per 100,000 people at risk each year. In France, there are about 4,370 cases per 100,000 at risk each year. In Finland, there are a reported 1,400-1,700 cases per 100,000 people at risk each year.

Author information
  • This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

Bibliography
  1. American Lung Association. Hypersensitivity Pneumonitis. . Accessed May 14, 2009.
  2. Lung Cancer Frontiers. Hypersensitivity Pneumonitis. . Accessed May 14, 2009.
  3. MedlinePlus. Hypersensitivity pneumonitis. . Accessed May 14, 2009.
  4. Natural Standard: The Authority on Integrative Medicine. . Copyright © 2009.
  5. University of Pennsylvania Health System. Hypersensitivity Pneumonitis. . Accessed May 14, 2009.

Causes
  • Hypersensitivity pneumonitis occurs after exposure to inhaled allergens, such as dust, animal dander, mold spores or plants.
  • Hypersensitivity pneumonitis is typically considered an occupational illness and has unique names that reflect the associated occupation. More than 300 etiologies of hypersensitivity pneumonitis have been reported from a wide range of airborne antigens. Examples include: farmer's lung (due to thermophilic actinomycetes and other pathogens), winemaker's lung (due to Botrytis cinerea), coffee-worker's lung (due to coffee-bean dust), lifeguard lung (due to aerosolized endotoxin), bird-fancier's lung (due to avian antigens), laboratory-worker's lung (due to rodent antigens), miller's lung (due to wheat weevil), woodworker's lung (due to Penicillium chrysogenum), detergent-worker's lung (due to Bacillus subtilis) and epoxy-resin lung (due to phthalic anhydride).
  • Farmer's lung is the most common form of hypersensitivity pneumonitis. It is caused by thermophilic actinomycetes and other pathogens that grow on hay, straw, grains and other organic materials found on farms.
  • The most common type of hypersensitivity pneumonitis among children is called bird-fancier's lung. This disease is usually caused by allergens (avian or animal proteins) associated with small, caged birds that are kept as domesticated pets.
  • The summer form of the disease is typically found in Japan, where the condition is attributed to the growth of mold in older wooden homes during the hot, humid summer months when spores are released. This form clears up by mid autumn and recurs the following year in sensitive individuals who are continually exposed to the mold spore allergens.
  • There is no evidence that cigarette smoking causes hypersensitivity pneumonitis. However, smoking cigarettes may aggravate the symptoms of a person who has the disease. Tobacco smoke temporarily paralyzes the cilia (small hairs) the line the bronchial tubes. The cilia are designed to filter irritants out of the airways. However, when the cilia are paralyzed, irritants remain in the bronchial tubes and infiltrate the alveoli, inflaming the tissue and breaking down the elastic fibers.

Symptoms
  • Symptoms vary from mild to severe. Acute symptoms may last up to three weeks, and symptoms often include shortness of breath, cough, burning sensation in the chest, malaise, chills and fever. The symptoms may persist for as little as 12 hours or as long as 10 days. Between attacks, the person may experience no symptoms.
  • Chronic hypersensitivity pneumonitis lasts longer than three weeks. After repeated exposure to an allergen, a chronic cough may develop with excessive sputum, which often contains pus. The patient may also develop a chronic shortness of breath, decreased appetite and weight loss. Clubbing (enlarged fingers and toes) is seen in about 50% of patients with chronic hypersensitivity pneumonitis. Tachypnea (rapid breathing), respiratory distress and rales (crackling sound in the chest, as a result from fluid in the alveoli) may occur.
  • Chronic hypersensitivity pneumonitis may lead to pulmonary fibrosis (scarring of the lung tissue), which is usually irreversible.

Diagnosis
  • Blood test: A qualified healthcare provider may perform a blood test to help detect allergies.
  • Challenge test: A challenge test may be performed under expert medical supervision to confirm a diagnosis. During the test, the individual inhales the suspected allergen in a controlled setting and the physician looks for symptoms. This type of test should only be performed by a qualified healthcare provider because it may provoke severe allergic reactions.
  • CT-scan: A high-resolution CT-scan of the lungs may be performed to confirm a diagnosis.
  • History: A detailed history is needed in order to determine whether the occurrence of symptoms may be related to environmental exposure.
  • Lung biopsy: A lung biopsy may be performed to distinguish the condition from other lung diseases. If an individual tests positive for the disease, findings may include small, poorly formed noncaseating granulomas near the respiratory or terminal bronchioles, patchy mononuclear cell infiltration (lymphocytes and plasma cells) of alveolar walls and large histiocytes with foamy cytoplasm in the interstitium.
  • Physical exam: During the physical exam, rales (crackling sound in the chest caused by fluid in the alveoli) may be heard when a healthcare provider listens to the patient's chest with a stethoscope.
  • X-ray: A chest X-ray and lung function test may show effects of the disease during acute episodes or during the chronic stage of the disease. However, the test results may appear normal between episodes when the patient shows no symptoms. These test results are not specific for hypersensitivity pneumonitis, and positive results may be due to other causes.

Treatment
  • Antigen avoidance: Individuals should avoid exposure to known allergens because the condition is reversible, if diagnosed early. Most patients recover completely after avoiding exposure to allergens.
  • Corticosteroids: Corticosteroids (like prednisone) may help decrease inflammation in the lungs in the short-term. Corticosteroid therapy has helped relieve symptoms dramatically after one or two months, according to research. However, the same studies also found that corticosteroids did not offer any added benefit in the long-term when compared to antigen avoidance or placebo. While corticosteroids may help relieve symptoms, they cannot cure the disease.
  • It may take up to three weeks to fully recover from an acute attack. Lung damage, such as pulmonary fibrosis, is permanent and may occur even after symptoms have subsided.
  • Most patients who have farmer's lung recover with only minor functional abnormalities in the lungs. Many farmers develop mild chronic lung impairment.
  • Bird fancier's lung, although not as well studied, appears to have a worse prognosis than farmer's lung. According to some research, 30% of bird fancier's lung cases are fatal within five years. The poorer prognosis may be the result of exposure to higher concentrations of the antigen, as well as more frequent exposure in the home environment, according to researchers.

Increased risk
  • Most individuals who have hypersensitivity pneumonitis are exposed to allergens (usually organic dusts) in daily work or personal life. The risk is greater when individuals are exposed frequently to high concentrations of the substances.
  • However, it is estimated that only about 5-20% of individuals exposed to the known allergens develop the disease.

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