Whenever we hear a disease labeled “idiopathic,” there is a good chance science just hasn’t caught up to understanding its full etiology. For example, silicosis, a disease thought to be “idiopathic” when first identified, is now conclusively linked to the inhalation of microscopic crystalline silica dust, which is an occupational hazard in the construction and mining industries.
In a systematic review and meta-analysis published in Scientific Reports this year, scientists examined various occupational and environmental risk factors that could have contributed to the development of idiopathic pulmonary fibrosis (IPF). Some of these risk factors, such as exposure to silica, wood dust, and metal dust, are long suspected to be linked to IPF.
Could IPF, like silicosis, be an occupational disease? Well, let’s first follow some cardinal clues. Although this is disputed, the study states “workers in agriculture, livestock industry, chemical, petrochemical industry, woodworking industry, and steel industry had higher risk of IPF.” If workers in these industries do indeed report a higher incidence of IPF, could their occupations be to blame?
Read more about IPF differential diagnosis
This study looked at research conducted across the globe, including in the US, Japan, Sweden, Southern Europe, Mexico, Egypt, and South Korea. All studies looked at the occupational and/or environmental exposure risk factors of developing IPF.
In the studies that were reviewed, the mean age of the subjects ranged between 50 and 75 years; in 4 of the 8 studies, the age-sex distribution between the IPF group and the control group was matched without statistically significant differences. The age range of 50 to 75 is significant because, assuming that the subjects started work around their 20s and remained in the same job for their whole life, their exposure to any occupational hazard would be at least 30 years, which is significant for an association to be made between occupation and the risk of developing IPF.
The Relationship Between Occupational and Environmental Exposure Factors and IPF
Metal Dust Exposure
Seven studies investigated metal dust exposure; 3 showed an increased risk of developing IPF, and 4 did not. However, it should be noted that the definition of “metal dust exposure” differed slightly between studies, and one investigated metal dust and metal fumes separately. Overall, the findings showed an increased risk of IPF with an odds ratio of 1.83 (95% CI, 1.15-2.91, P =.01, I2=54%).
Wood Dust Exposure
Four studies looked at the relationship between wood dust exposure and the risk of developing IPF. Once again, the definition of “wood dust” differed slightly in the different studies; one investigated wood dust and wood preservatives as one risk factor, and another separated the “wood dust” classification into wood dust, hardwood dust, and birch. Overall, the findings showed an increased risk of IPF with an odds ratio of 1.62 (95% CI, 1.04-2.53, P =.03, I2=5%).
Stone/Sand Dust Exposure
Four studies investigated the relationship between stone/sand dust exposure and the risk of developing IPF. One study looked only at stone, glass, and concrete dust, and another looked at stone and sand dust exposure containing silica. Overall, the findings showed an increased risk of IPF with an odds ratio of 2.27 (95% CI, 0.92-5.60, P =.06, I2=56%).
Textile Dust Exposure
Four studies investigated the relationship between textile dust exposure and the risk of developing IPF. The risk of developing IPF did not significantly increase, with an odds ratio of 1.26 (95% CI, 0.85-1.86, P =.25, I2=0%).
Four studies investigated the relationship between pesticide exposure and the risk of developing IPF. In this case, the odds ratio was 2.07 (95% CI, 1.24-3.45, P =.005, I2 = 0%).
The studies analyzed the risk factor of specific industries (construction, agriculture, and woodworking) with mixed results. However, we can conclude from these previous case-control studies that “metal dust increases the risk of IPF” and “wood dust increased IPF with statistical significance.” In addition, exposure to “livestock like cattle and birds, livestock feed, pesticides, mold, soil dust, stone dust, stone polishes, and smoke increases IPF prevalence.”
A lot of research has gone into demystifying other diseases that are popularly thought to have an idiopathic origin, such as fibromyalgia. These findings alone suggest certain exposures drive up the risk of IPF, and the disease is not as “idiopathic” as it may seem.
Read more about IPF experimental therapies
Our Role as Clinicians
As clinicians, this should encourage us to take a thorough history of our patients’ current and previous occupations, as they may shine some light on the origin of the disease — even if they may not seem immediately relevant to the presenting signs and symptoms.
The interesting question left unanswered in this study is what exactly the threshold is for a disease to no longer be considered “idiopathic”. The study had a concrete conclusion: “meta-analysis of patient-control studies revealed that exposure to pesticides, metal dust, and wood dust increases the risk of IPF.” This means that exposure to these risk factors should be investigated as part of robust history taking, especially if chest imaging and laboratory findings support a diagnosis of IPF.
This is not always the case in practice. In cases of diseases of idiopathic origins, clinicians tend to move on quickly from investigating the source of the disease to diagnosing and treating it. This is oftentimes done with the best of intentions, with the goal of restoring the patient’s health as quickly and effectively as possible.
However, a greater emphasis on disease prevention would inevitably mean a greater focus on clearly identifying the etiology of a disease. To steer us towards a more preventative approach, workers in high-risk occupations should demand better protection against the possible development of diseases like IPF in the long run. And if corporations fail to comply with basic health standards, they should be held accountable, just like in the case of scoliosis. For us to facilitate this, we need to be better at uncovering — and documenting — the possible origins of an “idiopathic” disease like IPF.
Park Y, Ahn C, Kim TH. Occupational and environmental risk factors of idiopathic pulmonary fibrosis: a systematic review and meta-analyses. Sci Rep. 2021;11:4318. doi:10.1038/s41598-021-81591-z
Silicosis. American Lung Association. Accessed July 10, 2021.
Hulens M, Dankaerts W, Stalmans I, et al. Fibromyalgia and unexplained widespread pain: the idiopathic cerebrospinal pressure dysregulation hypothesis. Med Hypotheses. 2018;110:150-154. doi:10.1016/j.mehy.2017.12.006.