RESEARCH - Silica exposure among male current smokers is associated with a high risk of developing ACPA positive RA

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Ann Rheum Dis. Published Online First: 4 December 2009.

doi:10.1136/ard.2009.114694

Silica exposure among male current smokers is associated with a high

risk of developing ACPA positive rheumatoid arthritis

Patrik Stolt1,*, Abqariyah Yahya2, Camilla Bengtsson1, Henrik

Källberg1, Johan Rönnelid3, Ingvar Lundberg4, Lars Klareskog5, Lars

Alfredsson1, the EIRA study group6

1 Institute of Environmental Medicine, Karolinska Institutet, Sweden;

2 Institute of Environmental Medicine, Karolinska Institutet and

Institute for Medical Research, Jalan, Sweden;

3 Unit of Clinical Immunology, Uppsala University and Rheumatology

unit, Department of Medicine, Karol, Sweden;

4 Department of Occupational and Environmental Medicine, Uppsala

University Hospital, Sweden;

5 Rheumatology unit, Department of Medicine, Karolinska Institutet at

Karolinska Hospital, Solna, Sweden;

6 -, Sweden

ABSTRACT

Objective: To study the association between silica exposure,

separately as well as combined with smoking, and the risk of

developing Rheumatoid Arthritis (RA) with or without presence of

antibodies against citrullinated peptide antigens (ACPA).

Methods: This Swedish population based case-control study analysed 577

incident RA cases and 659 randomly selected controls, all men aged

18-70 years, included during May 1996 – May 2006. Self-reported silica

exposure, defined as exposure to stone dust, rock drilling or stone

crushing, and cigarette smoking was registered. ACPA status among

cases was analysed.

Results: Silica exposed persons were observed to have a moderately

increased risk of ACPA positive RA (odds ratio (OR) adjusted for age

and residency = 1.67 (95% confidence interval (95% CI) 1.13-2.48)),

but not of ACPA negative RA (OR = 0.98 (95% CI 0.57-1.66)), compared

with persons unexposed to silica. Persons exposed to rock-drilling

were observed to have a somewhat more markedly increased risk of ACPA

positive RA (OR = 2.34 (95% CI 1.17-4.68)). A high risk of developing

ACPA positive RA was observed among silica exposed current smokers (OR

= 7.36 (95% CI 3.31-16.38)), exceeding what was expected from the

separate effects of silica exposure and current smoking, indicating an

interaction between these exposures (attributable proportion due to

interaction = 0.60 (95% CI 0.26-0.95)).

Conclusion: Silica exposure combined with smoking among men is

associated with increased risk of developing ACPA positive RA. These

results suggest that different inhalation exposures may interact in

the aetiology of ACPA positive RA.

http://ard.bmj.com/cgi/content/abstract/ard.2009.114694v1?papetoc

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