What is hypersensitivity pneumonitis and what
are its
causes?
Hypersensitivity pneumonitis (HP) is an inflammation of the
lung (usually of the very small airways) caused by the body’s immune
reaction to small air-borne
particles. These particles can be bacteria, mold, fungi, or even
inorganic matter.
What is acute hypersensitivity pneumonitis?
Acute hypersensitivity pneumonitis tends to occur 4-12 hours after exposure (usually heavy exposure) to the particles.
What are the symptoms of acute hypersensitivity pneumonitis?
Symptoms of acute hypersensitivity pneumonitis include:
- Coughing
- Body aches, malaise
Chest X-ray may show diffuse small nodules in the lungs. Typically, the symptoms will subside hours to days after exposure (provided there are no repeated exposures). The
abnormalities on chest X-ray abnormalities will also disappear. The
patient’s condition can deteriorate after exposure; therefore it is imperative
that a medical evaluation be performed to determine the best course of
treatment.
What is chronic hypersensitivity pneumonitis?
Chronic (long-term) hypersensitivity pneumonitis causes
lung scarring (fibrosis).
What are the symptoms of chronic hypersensitivity pneumonitis?
Symptoms of chronic hypersensitivity pneumonitis include:
- Shortness of breath
- Cough
Chronic disease is believed to occur after prolonged low grade exposure to the offending particles.
It is sometimes quite surprising that individuals with a passion for their
hobbies or occupation will continue to allow exposure to lung damage (if the
offending particles are related to the hobby or job) despite the knowledge that
it is harmful.
What are examples of hypersensitivity pneumonitis?
Examples of hypersensitivity pneumonitis include:
- Farmer’s lung disease from exposure to mold spores in hay
- Pigeon breeder’s disease from exposure to protein particles in
pigeon droppings - Sauna takers’ disease from exposure to mold growing in wet
containers - Mushroom workers’ disease from exposure to moldy compost
- Bagassosis from exposure to moldy sugar cane
- Winemaker's lung from exposure to a fungus on grapes called
Botrytis cinerea - An unusual case was published involving a case of hypersensitivity to
Canadian goose droppings. The individual was a physician who was exposed
to both indoor and outdoor antigens while living in a suburban Illinois
community. One can only imagine the tremendous detective work necessary to
make this diagnosis.
A more detailed analysis is listed in the table, which includes the
types of compounds, bacteria, and molds known to cause hypersensitivity
pneumonitis.
Bacteria (Thermophilic actinomycetes)
Moldy bagasse (pressed sugarcane)
Bacteria (Thermophilic actinomycetes)
Mushroom compost
Bacteria (Mycobacterium immunogenum)
Mist from metalworking fluids
Bacteria (Mycobacterium avium complex)
Mist from hot tubs
Bacteria (Endotoxin)
Indoor swimming pool
Bacteria (Thermophilic actinomycetes)
Fungus (Aspergillus species)
Moldy hay
Bacteria (T. candidus, Bacillus subtilis, B. cereus, Klebsiella oxytoca)
Fungus (Aureobasidium pullulans)
Amoebae (Naegleria gruberi, Acanthamoeba polyhaga, Acanthamoeba castellani)
Mist from standing water
Fungus (Aspergillus)
Compost
Fungus (Aspergillus clavatus)
Moldy barley
Fungi (Monocillium sp, Penicillium citreonigrum)
Peat moss
Fungus (Penicillum frequentans)
Moldy cork dust
Fungus (Cryptostroma corticale)
Moldy wood bark
Fungus (Alternaria species)
Moldy wood pulp
Fungus (Rhizopus species)
Moldy wood trimmings
Fungi (Penicillium (three species), Paecilomyces sp.,
Aspergillus niger, Aspergillus sp., Rhizopus sp.)
Wood chips from living maple and oak trees
Fungus (Merulius lacrymans)
Moldy rotten wood
Fungi (Graphium species, Pullularia species)
Moldy wood dust
Fungus (Trichosporon cutaneum)
Damp wood and mats
Fungus (Pencillum casei or P.roqueforti)
Cheese casings
Fungus (Aspergillus sp.)
Moldy tobacco
Fungi (Aspergillus sp., Penicillium sp., Cryptostroma corticale)
Moldy soil
Fungus (Aspergillus fumigatus)
Moldy esparto used to produce ropes, canvas, sandals, mats, baskets, and paper paste
Fungus (Aspergillus oryzae)
Fermentation starter for soy sauce
Avian proteins
Bird droppings and feathers
Aquatic animal proteins
Mollusc shell dust
Animal proteins
urine, serum, fur
Wheat weevil (Sitophilus granarius)
Infested flour
Silk worm larvae proteins
Silk worm larvae
TDI, HDI, MDI
Paints, resins, polyurethane foams
Trimellitic anhydride
Plastics, resins, paints
Rose, CS, Lara AR. Hypersenstivity pneumonia In: Mason RJ, Broadus VC, Martin TR, et al. Eds. Murray and Nadel’s Textbook of Respiratory Medicine. 5th ed. Philadelphia, Pa; Saunders Elsevier; 2010; Chap 66.
How is hypersensitivity pneumonitis diagnosed?
Many people with episodes of hypersensitivity pneumonitis are probably unrecognized and undiagnosed. Some cases believed to be viral pneumonias may actually be hypersensitivity pneumonitis. The patient’s history of repeated episodes of typical symptoms, hours after exposure to certain environments are important in establishing the diagnosis.
Most patients with this disorder have symptoms of shortness of breath and/or cough. Quite often a chest
X-ray may show a variety of abnormalities, but primarily increased lung markings. A specialist in lung disease will primarily depend on a history of exposure either by occupation or hobby. With the abnormal chest X-ray, a high resolution cat scan of the chest is often reviewed. This study shows a detailed image of the appearance of the lung tissue. Lung function tests that examine the lung volumes and the ability for gases to move through the lungs (diffusing capacity) are then performed. Not only are the
CT scan and pulmonary function tests useful in diagnosis but they are also useful in following response to therapy.
Blood antibody tests and skin tests against certain offending molds, bacteria, or particles are available, but their results are usually inconclusive. Other more recent tests such as the serum KL-6 (Krebs von den Lungen-6; this test may act as a marker for activity seen in diffuse lung disease) may be used. Infectious causes as well as collagen vascular diseases and
cancer must be excluded as a cause of the symptoms and signs, and this may involve a biopsy. Unfortunately the small biopsies obtained with a bronchoscope or a needle are usually inadequate. It is often necessary to perform Video Assisted Thoracoscopic Surgery (a.k.a. VATS), which is an open lung biopsy technique performed by thoracic surgeons under general anesthesia. This procedure allows for a larger sample size and more accurate diagnosis.
The interpretation of these tests is complicated, and is best performed by a doctor experienced in hypersensitivity pneumonitis, often with the help of a pathologist experienced in lung diseases. The most accurate determination of the cause of hypersensitivity pneumonitis is almost always a detailed exposure history. It is not uncommon, however, to be unable to find the causative agent.
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What is the treatment for hypersensitivity pneumonitis?
The most important treatment of hypersensitivity pneumonitis is avoidance of repeated exposures to the offending particles. With early diagnosis and prevention, the prognosis is good. Prolonged, repeated exposures can lead to permanent lung damage, scarring, and potentially significant disability.