Interleukin-6 serum concentration in ankylosing spondylitis: a reliable predictor of disease progression in the subsequent year?

The aim of the present study was to evaluate whether in ankylosing spondylitis (AS), interleukin-6 (IL-6) is a reliable predictor of changes in mobility in the subsequent year. Of 261 AS patients who had been enrolled in a previous study, 128 returned for treatment at our health centre after 1 year (+/-3 months). The variables for mobility after 1 year (II) were compared with the findings of the previous year (I). Differences in parameters for mobility were related to the serum concentration of IL-6 in the previous year. Relation between serum concentration of IL-6 and difference (II-I) in occiput-to-wall distance (Spearman's rank correlation coefficient r(s), P value) was 0.02, 0.82; chin-chest distance -0.09, 0.31; cervical rotation -0.08, 0.39; chest expansion 0.05, 0.54; finger-floor distance -0.02, 0.84; Ott sign (flexibility of the thoracic spine) -0.11, 0.22; Schober sign 0.01, 0.94. After 1 year there was a significant improvement in cervical rotation in patients with low IL-6 serum concentration (lower quartile), but not in those with high levels of IL-6 (upper quartile). No further difference was seen between patients with high or low levels of IL-6. The present data suggest that the serum concentration of IL-6 does not allow a prediction of disease progression in the subsequent year.