Clinical correlates of urolithiasis in ankylosing spondylitis

To determine the association between urolithiasis and syndesmophyte formation and the effect of urolithiasis on ankylosing spondylitis (AS) disease activity.

In a longitudinal cohort of 504 patients with AS, we conducted an analysis of all patients with AS who have a history of urolithiasis. All patients met the modified New York criteria for AS. Demographics, clinical characteristics, extraarticular features, and comorbidities are systematically recorded in the database. We compared disease activity, functional indices, medical therapy and radiographic damage between AS patients with (Uro+) and without urolithiasis (Uro-) using the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS).

Thirty-eight patients with AS (7.5%) had a history of urolithiasis in our cohort. Seventy-six patients with AS who did not have urolithiasis, matched for age, sex, and ethnicity, were selected as controls. Patients who were Uro+ were more likely to have more functional disability, based on the Bath AS Functional Index (BASFI; mean 5.3 vs 3.6 in control group, p = 0.003). Trends were noted in the Uro+ group toward higher Bath AS Disease Activity Index (BASDAI; mean 4.9 vs 4.0, p = 0.09), more peripheral joint involvement (p = 0.075), and higher frequency of biologic therapy (p = 0.09). No significant difference was detected in mSASSS or the Bath AS Metrology Index (BASMI). Significant association with diabetes mellitus (DM; p = 0.016) and Crohn's disease (p = 0.006) was noted in the Uro+ group.

Although there is no acceleration of syndesmophyte formation or spinal mobility restriction, more functional disability was detected in the urolithiasis group. The higher risk with concomitant DM or Crohn's disease should alert clinicians to these comorbidities in Uro+ patients with AS.