only four exposed cases. The authors noted that there were only small differences in the risk of rheumatoid arthritis among the different occupations. The jobs studied often involved manual labor. It is possible that people with rheumatoid arthritis are less likely to seek such jobs (because of pain or deformity of their hands) and that the study therefore underestimated the association. Conversely, it is possible that rheumatoid arthritis was more likely to be diagnosed in people whose work required the use of their hands and that the study therefore overestimated the association.

Undifferentiated connective-tissue disorder (UCTD) is the term used to describe a condition with nonspecific rheumatic symptoms that do not meet the criteria for any specific rheumatic disease. Lacey and colleagues (1999) conducted a case-control study involving 205 females with UCTD, compared with 2095 population-based female control subjects identified by random-digit dialing. Interviews were conducted to assess occupational exposures to solvent-containing products and to specific solvents. The study reported an elevated risk of UCTD with painting or paint manufacturing (OR=2.87, 95% CI=1.06–7.76) and with some solvents and solvent products. Of 32 patients reporting exposure to paint thinners or paint removers, the OR was 2.73 (95% CI=1.80–4.16). For 18 patients exposed to mineral spirits, naphtha, or white spirits, the OR was 1.81 (95% CI=1.09–3.02). Analyses for trichloroethylene, toluene, and other specific solvents involved few exposed cases and did not show consistent increases in risk. Control for confounding included adjustments for age at diagnosis and year of birth. The study was subject to strong recall bias.

Summary and Conclusion

The studies reviewed by the committee have reported inconsistent results for an association between systemic rheumatic diseases and exposure to solvents (Table 9.5). As with studies of other health effects, the exposures lack specificity and their assessments involve the use of job categories with wide variations in exposure. Although there is an indication of elevated risks in several studies of scleroderma and exposure to solvents, additional studies using control groups could clarify the nature of this association.

The committee concludes, from its assessment of the epidemiologic literature, that there is inadequate/insufficient evidence to determine whether an association exists between chronic exposure to specific organic solvents under review or solvent mixtures and the systemic rheumatic diseases: scleroderma, rheumatoid arthritis, undifferentiated connective tissue disorders, and systemic lupus erythematosus.

TABLE 9.5 Selected Epidemiologic Studies: Systemic Rheumatic Diseases and Exposure to Organic Solvents

Reference

Population

Exposed Cases

Estimated Relative Risk (95% CI)

Scleroderma

Case-Control Studies

Lundberg et al., 1994

Swedish residents with systemic sclerosis

 

 

Aliphatic hydrocarbon exposure

6

2.1 (0.8–5.5)

Silman et al., 1992

Scleroderma cases in the United Kingdom

18

 

 

Organic solvent exposure

 

 

Compared with general practitioner controls

 

1.7 (0.7–4.1)

 

Compared with friend controls

 

2.3 (0.9–6.2)



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