Is Idiopathic Pulmonary Fibrosis (IPF)?
is a specific form of chronic fibrosing interstitial pneumonia, limited
to the lung, and associated with the histologic appearance of UIP
[Usual Interstitial Pneumonia] on
surgical (thoracoscopic or open) lung biopsy. The aetiology is
unknown. The definite diagnosis of IPF in the presence of a surgical
biopsy showing UIP includes the following. 1. Exclusion of other
known causes of interstitial lung disease such as drug toxicities,
environmental exposures, and collagen vascular diseases. 2. Abnormal
pulmonary function studies that include evidence of restriction
and/or impaired gas exchange. 3. Abnormalities on conventional chest
radiographs or high-resolution computed tomography (HRCT). . . . All
IPF is UIP, but on the other hand, not all UIP is IPF." 1 IPF,
as it was defined in the past, is the most common nonoccupational cause of
interstitial lung disease--about 25% to 40% of the cases. [Harber,
IPF an Occupational Disease?
IPF is not an occupational disease; it is an idiopathic disease, meaning that
the cause is unknown.
the Diagnosis of IPF Changed in Recent Years?
the definition of IPF was much broader 20 years ago. "UIP is the
histopathological pattern that identifies patients with IPF. Other patterns such
as DIP, respiratory bronchiolitis-associated interstitial lung
disease (RBILD), NSIP, LIP, AIP, and idiopathic bronchiolitis
obliterans organising pneumonia (idiopathic BOOP) are considered
separate entities and are to be excluded from the group of patients
with IPF." A surgical lung biopsy is now recommended for most patients.1
Are the Most Common Causes of Occupational Interstitial Lung Disease?
most common causes are silica, asbestos, coal, beryllium, and hard-metal cobalt.
Other minerals and metals are listed in Haz-Map linked to benign and other pneumoconioses.
Also, moldy organic mists and dusts cause hypersensitivity
pneumonitis in a variety of occupations, including workers exposed to farm
dusts, wood dusts, birds, and metalworking fluids (MWFs). See Table
1. Also see Interstitial
Lung Disease in Haz-Map at the NLM website. Hypersensitivity pneumonitis in the chronic stage causes interstitial
fibrosis. Precipitating antibodies are neither sensitive nor specific, and their
presence is no longer considered a hallmark of HP. [Murray,
p. 1783-99] Symptoms of asbestosis are slower in developing, and patients with
asbestosis have less respiratory impairment than patients with IPF. [Rom,
Case Control Studies Prove that IPF Is Caused by Metal and Wood Dusts?
control studies show that patients with IPF, as it was broadly defined in the
past, are more likely to report occupational dust exposures than people in the
control group. 2,3,4,5 One of the weaknesses of case control studies
is recall bias, meaning that the validity of recall about past exposures may
vary between people who have a chronic lung disease and those who don't. Since
these case control studies used the old case definition of IPF, it is possible
that many of the patients were misdiagnosed. For example, in the Baumgartner et
al paper2, negative serum precipitin tests were used to rule out
hypersensitivity pneumonitis, but it is now known that these tests are not
reliable. As noted in a another recent paper, "Hypersensitivity pneumonitis
due to exposure to MWFs is under-recognized by health care providers, and
current surveillance systems are inadequate to provide a true estimate of its
occurrence."6 As noted by Taskar and Coultas, "Given the
low utilization of the gold standard for diagnosing IPF and the complexity of
diagnosis, there is high likelihood for misdiagnosis."3
- International consensus statement on idiopathic pulmonary fibrosis. Full
and environmental risk factors for idiopathic pulmonary fibrosis: a
multicenter case-control study. Full text at: http://aje.oxfordjournals.org/cgi/reprint/152/4/307
idiopathic pulmonary fibrosis an environmental disease? Full text at: http://pats.atsjournals.org/cgi/content/full/3/4/293
and environmental factors and idiopathic pulmonary fibrosis in Japan.
Full text at: http://annhyg.oxfordjournals.org/cgi/content/full/49/3/259
exposure and severe pulmonary fibrosis.
pneumonitis due to metal working fluids: Sporadic or under reported?