ABSTRACT: Occupational exposure to various chemicals, minerals, and toxins may increase the risk of rheumatoid arthritis (RA). Relationships between silica exposure and lung, renal, and autoimmune disease have been observed. Although a relationship between silica exposure and RA has been identified, it is not well defined. The evidence indicating that cigarette smoking is an independent risk factor for RA is conclusive. Agents that may be capable of inducing experimental arthritis in animals include adjuvants from bacteria, yeast, viruses, and mineral oils. In a Swedish study, exposure to any mineral oil was associated with a 30% increased relative risk of RA. (J Musculoskel Med. 2008;25:130-136)
Autoimmunity, defined as the development of an immune system response in the form of autoantibodies and T-cell responses to self-structures, has been researched widely over the years because it is prevalent in men and women from childhood throughout their adult years. Patterns of disease occurrence in families and in animal models strongly suggest a role for genetic factors. The genes most frequently associated with autoimmunity are those that regulate immune responses and cytokine production.
Environmental factors also have been hypothesized to play a role in the development of autoimmune diseases. Studies have provided strong support for the concept that these diseases result from interactions of both genetic and environmental factors.
A growing amount of the medical literature now claims that the development of rheumatoid arthritis (RA) may be influenced by occupational exposure to various chemicals, minerals, and toxins (Table). Studies that examined the role of silica and mineral oil exposure in RA have found significant associations and increased risk. In this article,we review the existing epidemiological and experimental literature on occupational exposures and their correlation to the development of RA.
METHODS AND RESULTS
Cross-referencing the terms "occupational exposure" and "environmental exposure" with the term "rheumatoid arthritis," we searched MEDLINE (1966 - 2006) and PubMed (1966 - 2006) for articles in English that were human studies. Retrieved articles were selected based on their clinical relevance and applicability.
Silica exposure and increased health risk
Epidemiological evidence has stimulated investigation into occupational exposure to suspected pathogens and carcinogens and any resultant increased health risk.The relationship between occupational silica exposure and lung disease, primarily in occupations associated with mining, has a well-documented history; accounts of occupational exposure have accumulated much evidence indicating a direct increased health risk, specifically for lung pathology.1-3 More in-depth studies are related to exposure limits, occupations with increased risk, and additional health risks related to silica exposure.4-6
Relationships between silica exposure and renal disease and autoimmune disease also have been observed.2,7-11 A relationship between silica exposure and RA has been identified, although the relationship currently is not well defined.12
Coexisting pulmonary and rheumatologic findings
In the early 1950s, Caplan13 was one of the first to document the coexistence of pulmonary and rheumatologic findings, showing chest radiograph opacities in coal miners with known RA. Further studies investigated and confirmed the positive correlation between RA and silicosis and noted that lung fibrosis is more likely to develop in workers exposed to silica who have RA than others who have similar exposure.14
