Risk Factors for Diagnosis of Psoriatic Arthritis, Psoriasis, Rheumatoid Arthritis, and Ankylosing Spondylitis: A Set of Parallel Case-control Studies

Abstract

Objective To compare potential risk factors for the diagnosis of psoriatic arthritis (PsA), psoriasis, rheumatoid arthritis (RA), and ankylosing spondylitis (AS). Methods Four parallel case-control studies were conducted within The Health Improvement Network using data between 1994 and 2015. Patients with PsA, psoriasis, RA, or AS were identified using validated code lists and matched to controls on age, sex, practice, and year. Risk factors were selected in the time prior to diagnosis. Multivariable logistic regression models were constructed for each disease using automated stepwise regression to test potential risk factors. Results Patients with incident PsA (N=7,594), psoriasis (N=111,375), RA (N=28,341), and AS (N=3, 253) were identified and matched to 75,930, 1,113,345, 282,226, and 32,530 controls, respectively. Median diagnosis age was 48 (IQR 38-59), 41 (31-54), 43 (31-54), and 60 (48-71), respectively. In multivariable models, there were some shared and some differing risk factors across all 4 diseases: PsA was associated with obesity, pharyngitis, and skin infections; PsA and psoriasis were associated with obesity and moderate alcohol intake; PsA and AS were associated with uveitis; and PsA and RA were associated with preceding gout. Both RA and AS were associated with current smoking, former moderate drinking, anemia, osteoporosis, and inflammatory bowel disease. All shared former or current smoking as a risk factor; statin use was inversely associated with all 4 diseases. Conclusion Shared and different risk factors for PsA, psoriasis, RA, and AS were identified. Statin use was inversely associated with all 4 conditions.

Drs. Meer and Ogdie reply

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We thank Dr. Liao et al 1 for their letter and thoughtful comments about our study. 2 We agree that, in general, current drinking would theoretically have a stronger association with disease than past drinking. However, studying alcohol and the association with disease is notoriously difficult.

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A Roadmap for Investigating Preclinical Autoimmunity Using Patient-Oriented and Epidemiologic Study Designs: Example of Rheumatoid Arthritis

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“…The pathogenesis of AS is found to be associated with genetics, infection, environment, and immunity, 1 which also explains numerous identified risk factors for AS including smoking, uveitis, inflammatory bowel disease, and gastrointestinal infection. 2 Among SpA, AS is the most common. 3 Furthermore, AS shows a male predominance with a 3:1 male to female ratio, which indicates that androgens might have a role in the mechanism, although in previous studies, the androgen level in AS patients seemed to be controversial.…”