Pneumoconiosis, Pulmonary Fibrosis, and Interstitial Lung Disease:

 Do They Refer to the Same Disease Process?

The NLM has indexes (MeSH) for the various lung diseases that result in lung scarring (fibrosis):1

Pulmonary Fibrosis

A process in which normal lung tissues are progressively replaced by FIBROBLASTS and COLLAGEN causing an irreversible loss of the ability to transfer oxygen into the bloodstream via PULMONARY ALVEOLI. Patients show progressive DYSPNEA finally resulting in death.

Lung Diseases, Interstitial

A diverse group of lung diseases that affect the lung parenchyma. They are characterized by an initial inflammation of PULMONARY ALVEOLI that extends to the interstitium and beyond leading to diffuse PULMONARY FIBROSIS. Interstitial lung diseases are classified by their etiology (known or unknown causes), and radiological-pathological features. Year introduced: 1994

Pneumoconiosis

A diffuse parenchymal lung disease caused by inhalation of dust and by tissue reaction to their presence. These inorganic, organic, particulate, or vaporized matters usually are inhaled by workers in their occupational environment, leading to the various forms (ASBESTOSIS; BYSSINOSIS; and others). Similar air pollution can also have deleterious effects on the general population. Year introduced: 1966

Idiopathic Pulmonary Fibrosis

A common interstitial lung disease of unknown etiology, usually occurring between 50-70 years of age. Clinically, it is characterized by an insidious onset of breathlessness with exertion and a nonproductive cough, leading to progressive DYSPNEA. Pathological features show scant interstitial inflammation, patchy collagen fibrosis, prominent fibroblast proliferation foci, and microscopic honeycomb change. Year introduced: 2009

So, "pulmonary fibrosis," "interstitial lung disease," and "pneumoconiosis" are three terms that can refer to the same disease process (scarring or fibrosis) at the same anatomical site (the interstitium of the lung). The interstitium is the supporting lung tissue adjacent to pulmonary airways and blood vessels. Idiopathic pulmonary fibrosis is a subset of pulmonary fibrosis in which the cause is unknown after extensive testing and the lung biopsy shows the presence of usual interstitial pneumonia (UIP).2

The occupational interstitial lung diseases in Haz-Map include:

§  Asbestosis

§  Chronic beryllium disease

§  Coal workers' pneumoconiosis

§  Coal workers’ pneumoconiosis (CWP), complicated

§  Hard metal disease

§  Hypersensitivity pneumonitis

§  Pneumoconiosis, benign

§  Pneumoconiosis, other

§  Silicosis, acute

§  Silicosis, complicated

§  Silicosis, simple.3

Byssinosis is not classified as pneumoconiosis in Haz-Map, but as an "Airway Disease."

As noted in the chapter on "Pulmonary Fibrosis and Interstitial Lung Diseases" by Carrie A. Redlich "The term pneumoconiosis has traditionally been defined as the accumulation of dust in the lungs and the resulting tissue reaction."4 In that chapter, she shows Table 1 that lists the occupational and non-occupational causes of interstitial lung disease.

A similar list can be found on the Mayo Clinic website5, and the author brings up some excellent caveats.

·         Pulmonary fibrosis is the end stage of interstitial lung disease, a large group of disorders that cause progressive lung scarring.

·         The list of substances and conditions that can lead to pulmonary fibrosis is long. Even so, in most cases, the cause is never found. Pulmonary fibrosis with no known cause is called idiopathic pulmonary fibrosis.

·         Researchers have several theories about what might trigger idiopathic pulmonary fibrosis, including viruses and exposure to tobacco smoke. And because one type of idiopathic pulmonary fibrosis runs in families, heredity also is thought to play a role, even in people who don't directly inherit the disease.

·         Diagnosing pulmonary fibrosis can be extremely challenging. The difference between idiopathic and nonidiopathic forms of the disease isn't always clear, and the naming and classification systems for both have historically been confusing and controversial.

·         In addition, many medical conditions, including chronic obstructive pulmonary disease (COPD), asthma and even heart failure, can mimic pulmonary fibrosis, so doctors must rule these out before making a definitive diagnosis.

·         A complete medical history, physical exam and even a chest X-ray aren't enough to diagnose pulmonary fibrosis. For that reason, you may have tests such as a high-resolution computerized tomography (CT) scan, which provides sharper and more detailed images than conventional CT scans do; an exercise test on a treadmill or stationary bike to monitor your lung function when you're active; and pulmonary function tests to measure how well your lungs work overall.

·         Often, though, pulmonary fibrosis can be definitively diagnosed only by examining a small amount of lung tissue (biopsy) in a laboratory. The tissue sample may be obtained in one of these ways: [bronchoscopy, bronchoalveolar lavage, and surgical biopsy]

 

References

1.       National Library of Medicine. 2009. PubMed: MeSH. Available at http://www.ncbi.nlm.nih.gov/sites/entrez?db=mesh.

2.       International consensus statement on idiopathic pulmonary fibrosis. 2001. Full text available at http://www.erj.ersjournals.com/cgi/content/full/17/2/163.

3.       National Library of Medicine. 2009. Haz-Map: Interstitial Lung Disease. Available at http://hazmap.nlm.nih.gov/cgi-bin/hazmap_cgi?level=1&term=5&level1name=Interstitial+Lung+Disease&tree=Disease.

4.       Redlich CA. 1996. Pulmonary Fibrosis and Interstitial Lung Diseases. In: Harber P, Schenker MB, Balmes JR (eds). Occupational and Environmental Respiratory Diseases. St. Louis: Mosby, p. 216-217.

5.       MayoClinic.com. 2009. Pulmonary Fibrosis. Available at http://www.mayoclinic.com/health/pulmonary-fibrosis/DS00927/DSECTION=symptoms.

 

Table 1

[Redlich CA. Pulmonary Fibrosis and Interstitial Lung Diseases. In: Harber, p. 217]

 

More common causes of occupational interstitial lung diseases

1.       Free silica

2.       Silicates

a.       Fibrous-asbestos

b.       Mixed dust

3.       Coal

4.       Metals

a.       Beryllium

b.       Hard metal-cobalt

Less common causes of occupational interstitial lung diseases

1.       Silicates

a.       Talc

b.       Kaolin

c.        Diatomaceous earth

d.       Man-made vitreous fibers (MMVF)

e.       Mica

2.       Hydrocarbon-containing sedimentary rocks

a.       Graphite

b.       Oil shale

3.       Metals

a.       Tin

b.       Aluminum

c.        Antimony

d.       Barium

e.        Iron

f.        Titanium

4.       Irritant gases, fumes, vapors

a.       Sequelae of toxic pneumonitis

5.       Plastics

a.       Polyvinylchloride

b.       Toluene diisocyanate

6.       Organic dusts

a.       Bacteria

b.       Fungi

c.       Animal proteins

d.       Plant proteins

7.       Paraquat

Most common causes of nonoccupational interstitial lung disease

1.       Unknown etiology

a.     Idiopathic

b.     Sarcoidosis

c.      Bronchiolitis obliterans organizing pneumonia (BOOP)

2.       Collagen vascular diseases

a.     Rheumatoid arthritis;

b.     Progressive systemic sclerosis;

c.     Systemic lupus erythematosus;

d.     Mixed connective tissue disease

3.       Pulmonary granulomatoses: Wegener's granulomatosis; Bronchocentric granulomatosis

4.       Vasculitides: Churg-Strauss syndrome

5.       Lymphoproliferative disorders: Lymphomatoid granulomatosis

6.       Inherited disorders: Tuberous sclerosis; Neurofibromatosis; Cystic fibrosis

7.       Drugs and treatment (selected examples)

a.    Antibiotics (nitrofurantoin, penicillins, and sulfasalazine);

b.    Cardiac drugs (hydralazine, procainamide, and amiodarone);

c.     Antineoplastic agents (bleomycin, busulfan, methotrexate, cyclophosphamide, nitrosureas);

d.    Antiinflammatory agents (gold salts and penicillamine);

e.    Central nervous system drugs (diphenylhydantoin);

f.     Radiation;

g.    Oxygen;

h.    Bone marrow transplantation;

i.     Miscellaneous: Intravenous use of illicit drugs; Mineral oil; Silicone; Penicillamine

8.       Infections

a.    Viruses; Mycobacteria; Fungi

9.       Other

a.    Aspiration; Pulmonary edema; Pulmonary hemorrhage

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Revised: April 30, 2011

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