Personal and Family Medical History Correlates of Rheumatoid Arthritis
Introduction
Rheumatoid arthritis (RA) affects approximately 1% of the U.S. population and as many as 2% to 3% of persons over 60 years of age 1, 2. Women are more likely to be affected than men, for unknown reasons (1). The course of the disease varies widely, but it is generally associated with progressive disability and early mortality (3). There have been previous reports of immune-related comorbidities occurring among RA patients 4, 5. Certain immune-related conditions may be sequelae of RA from immunosuppressive treatment regimens; alternatively, these conditions may share etiologic features with RA. However, few previous studies have investigated whether comorbid conditions preceded RA diagnosis, or whether there may be a familial environmental or genetic component contributing to both diseases.
We examined associations of various medical conditions with incident and prevalent RA among women enrolled in the Agricultural Health Study (AHS). Analyses of associations with conditions that predate incident RA may provide clues about diseases that contribute to the development of RA. Although the timing of diagnoses is not clear in associations of prevalent RA with coexisting medical conditions, these analyses can provide useful information about the frequencies of comorbid conditions, which may have related pathologies. In addition, we studied family history of medical conditions as a risk factor for RA to shed light on diseases which may have a familial shared environmental or genetic component to their causation.
Section snippets
Study Population
The methods for the AHS and the confirmation of RA cases have been previously described 6, 7. The AHS is a prospective study of a cohort of licensed pesticide applicators (n = 52,395 private pesticide applicators; n = 4916 commercial pesticide applicators) and their spouses (n = 32,347) in Iowa and North Carolina, enrolled from 1993 to 1997. A baseline questionnaire was administered upon enrollment. The private applicators are primarily white (97.1%) and male (97.4%). More than 99% of spouses
Results
Of the 135 physician-confirmed RA cases included in the nested case-control study, the median age at diagnosis was 47 years. There were few demographic differences between cases and controls (see Table 1), except that cases were slightly more likely than controls to be from North Carolina than from Iowa.
The risk of incident RA was associated with personal medical history conditions (Table 2), including nonmelanoma skin cancer (OR = 4.4, 95% CI: 1.4–14.1), asthma or reactive lung disease (OR =
Discussion
Our results suggest that persons with certain medical conditions (nonmelanoma skin cancer, asthma, and cataract) are more likely to develop RA. These results may indicate common pathogenesis of an environmental or genetic nature between such diseases; alternatively, one disease may develop as an unintended result of treatment for the other condition. A family history of nonmelanoma skin cancer was associated with incident RA; nevertheless, this association was not present in all subanalyses and
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Cited by (0)
This research was supported, in part, by the Intramural Research Program of the National Institutes of Health, National Institute of Environmental Health Sciences, and National Cancer Institute. These institutes were responsible for establishment of the Agricultural Health Study cohort, and members of these institutes served as coauthors on this paper.