Silica exposure is associated with an increased risk of developing ACPA-positive rheumatoid arthritis in an Asian population: evidence from the Malaysian MyEIRA case–control study

Abstract

Objectives. Silica exposure has been associated with an increased risk of developing rheumatoid arthritis (RA), especially among smokers. In this study, we aimed at examining the association between silica exposure (and its interaction with smoking) and the risk of RA in the Malaysian population.

Methods. In total, 149 cases and 213 matched controls, all men, were included between August 2005 and December 2009. A case was defined as a person with early diagnosed RA using the 1987 American College of Rheumatology criteria for RA. Controls were randomly selected matched on sex, age and residential area. Silica exposure was defined as exposure to stone dust, rock drilling or stone crushing, and smoking status was categorized as ever/never cigarette smoking.

Results. An increased risk of anti-citrullinated protein antibody (ACPA)-positive RA (OR = 2.4, 95 % CI 1.0–5.6) was observed among those exposed to silica. Ever-smokers exposed to silica had a particularly high risk of developing ACPA-positive RA (OR = 7.5, 95 % CI 2.3–24.2), compared with never-smokers not exposed to silica. No association was found regarding ACPA-negative RA.

Conclusion. Our data demonstrate that exposure to both silica and cigarette smoke comprise risks for developing RA in the Malaysian genetic context. The findings expand a link between environmental lung exposures and ACPA-positive RA to Asian populations.

Keywords:

• Anti-citrullinated protein antibody (ACPA)
• Malaysia
• Rheumatoid arthritis
• Silica

Acknowledgments

We would like to thank the Director General of Health, Malaysia for his permission to publish this report. Special thanks to Dr Hanjeet Kaur, Dr S. Kasthoori, Dr Yuslina Mat Yusoff, Kee Chee Cheong, Mohd Hadzrik Nor Osman, Norziyana Idris, Laily Murat Saffie, Fadzilah Hana Mahpot, Fazilah Hanim Kornain, Mohd Arif Abd Aziz, Nor Hamimah Md Non, Salwa Hanim Zainal Alam and the members of MyEIRA study group for their dedication and excellent assistance in this study. We truly value the patients and controls for their great participation. We also would like to thank Dr. Eva Bagge, Department of Rheumatology, Sahlgrenska University Hospital, Gothenburg, Sweden, for translating the EIRA questionnaire from Swedish to English. This study was financially supported by Ministry of Health, Malaysia: MRG 7/2005, JPP-IMR 07-046, JPP-IMR 08-012, and JPP-IMR 08-006, and by the Swedish Medical Research Council (DNR 348-2009-6468) and Swedish Combine program.

Conflict of interest

None.