A longitudinal study of disease activity and functional status in a hospital cohort of patients with ankylosing spondylitis.

OBJECTIVE: To evaluate changes in functional status and disease activity and their determinants in patients with ankylosing spondylitis (AS) attending hospital, using the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and the Bath Ankylosing Spondylitis Functional Index (BASFI).
METHODS: Patients completed BASDAI and BASFI questionnaires annually from 1996 to 2001. Demographic and clinical data were collected. The mean first and last recorded scores were compared. The change per year and area under the curve per year for the BASDAI and BASFI were calculated. Relationships between demographic, clinical and longitudinal BASDAI/BASFI data were examined. Subgroup analyses were performed using the cross-sectional and longitudinal data.
RESULTS: Two hundred and seventy-nine BASDAI and 322 BASFI questionnaires were analysed. The BASFI increased [mean change 6.15, 95% confidence interval (CI) 1.9, 10.3, P = 0.005] but the BASDAI did not (mean change 0.87, 95% CI -3.96, 5.7, P = 0.71). First recorded scores were the best predictors of the cumulative scores per year. Patients with peripheral joint (P = 0.01) and hip (P<0.001) disease had higher mean BASFI scores. Males (P<0.001) and patients with spinal disease alone (P = 0.0014), iritis (P = 0.005) and late-onset AS (P = 0.002) became more functionally impaired over time.
CONCLUSIONS: Disease activity in this AS cohort remained relatively constant but there was functional decline. Initial BASDAI/FI can predict a severe disease course. PJD patients with peripheral joint disease were more functionally impaired, but deteriorated less than spinal disease alone patients. Iritis and late onset disease may be severity markers for functional impairment.