Association of Asthma with Rheumatoid Arthritis: A Population-Based Case-Control Study.

BACKGROUND: TH 1 and TH 2 cells have counterregulatory relationships. However, the relationship between asthma, a TH 2-predominant condition, and risk of systemic inflammatory diseases such as rheumatoid arthritis (RA), a TH 1 condition, is poorly understood.

OBJECTIVE: We aimed to determine whether asthma was associated with increased risks of incident RA among adults.

METHODS: We conducted a retrospective population-based case-control study that examined existing incident RA cases and controls matched by age, sex, and registration year from the general population in Olmsted County, Minnesota, between January 2002 and December 2007. We performed comprehensive medical record reviews to ascertain asthma status using predetermined asthma criteria. The frequency of a history of asthma before the index date was compared between cases and controls. Logistic regression models were used to adjust for confounding factors.

RESULTS: We enrolled 221 RA cases and 218 controls. Of the 221 RA cases, 156 (70.6%) were females, 207 (93.7%) were white, the median age at the index date was 52.5 years, and 53 (24.0%) had a history of asthma. Controls had similar characteristics except that 35 of 218 controls (16.1%) had a history of asthma. After adjustment for sex, age, smoking, body mass index, socioeconomic status, and comorbidity, asthma was significantly associated with increased risks of RA (adjusted odds ratio, 1.74; 95% CI, 1.05-2.90; P = .03).

CONCLUSIONS: Despite the counterregulatory relationship between TH 1 and TH 2 cells, patients with asthma had a significantly higher risk of developing RA than healthy individuals.