Development and validation of a case ascertainment tool for ankylosing spondylitis

Ankylosing spondylitis (AS) diagnosis is often delayed. The availability of effective biologic agents for treating AS has increased the importance of early diagnosis. We tested questions derived from a comprehensive literature review and an advisory board in a case-control study designed to identify patients with AS from among patients with chronic back pain (CBP).

Question items were cognitively tested among patients with AS, and then in case-control studies for validation and creation of a scoring algorithm and question item reduction. AS cases were recruited from a known database, and CBP subjects (controls) were recruited from clinics, employers, and from the SpineUniverse Web site. We used individual question items in a multivariate framework to discriminate between people with and without AS.

Forty-three questions yielded 24 items for analyses; 12 of these were entered into a multivariate regression model. Individual items yielded odds ratios ranging from 0.07 to 30.31. Question items with a significant positive relationship to AS included male sex, neck or hip pain/stiffness, longer pain duration, decreased pain/stiffness with daily physical activity, pain relief within 48 hours of nonsteroidal antiinflammatory drugs, and diagnosis of iritis. The tool demonstrated a sensitivity of 67.4 and a specificity of 94.6. The tool was developed from clinically and radiologically diagnosed AS cases and therefore is designed to distinguish AS cases among CBP subjects. In addition, approximately 54% of the AS cases in the study were treated with biologic agents, which may impact questionnaire responses.

This tool can identify undiagnosed patients with AS and, potentially, those at an earlier stage in their disease course.