Silica exposure among male current smokers is associated with a high risk of developing ACPA-positive rheumatoid arthritis.
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 the 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 to 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 subjects were found to have a moderately increased risk of ACPA-positive RA (odds ratio (OR) adjusted for age and residency=1.67 (95% CI 1.13 to 2.48), but not of ACPA-negative RA (OR=0.98 (95% CI 0.57 to 1.66)), compared with subjects unexposed to silica.


METHODS
exposed to rock drilling were found to have a somewhat more markedly increased risk of ACPA-positive RA (OR=2.34 (95% CI 1.17 to 4.68)). A high risk of developing ACPA-positive RA was observed among silica-exposed current smokers (OR=7.36 (95% CI 3.31 to 16.38)), exceeding the risk 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 to 0.95)).


CONCLUSIONS
Silica exposure combined with smoking among men is associated with an increased risk of developing ACPA-positive RA. These results suggest that different inhalation exposures may interact in the aetiology of ACPA-positive RA.
Stolt
Patrik
P
Institute of Environmental Medicine, Karolinska Institutet, Box 210, S-171 77 Stockholm, Sweden. patrikstolt@swipnet.se
Yahya
Abqariyah
A
Bengtsson
Camilla
C
Källberg
Henrik
H
Rönnelid
Johan
J
Lundberg
Ingvar
I
Klareskog
Lars
L
Alfredsson
Lars
L
D000293:Adolescent; D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000453:epidemiology / Q000209:etiology* / Q000276:immunology; D001323:Autoantibodies / Q000097:blood; D016022:Case-Control Studies; D006801:Humans; D019570:Inhalation Exposure / Q000009:adverse effects / Q000032:analysis; D008297:Male; D008875:Middle Aged; D016273:Occupational Exposure / Q000009:adverse effects / Q000032:analysis; D010456:Peptides, Cyclic / Q000276:immunology; D012822:Silicon Dioxide / Q000009:adverse effects*; D012907:Smoking / Q000009:adverse effects* / Q000453:epidemiology; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult
D001323:Autoantibodies; D010456:Peptides, Cyclic; C487763:cyclic citrullinated peptide; D012822:Silicon Dioxide