## Arthritis & Rheumatism, Volume 60,

October 2009 Abstract Supplement

The 2009 ACR/ARHP Annual Scientific Meeting

Philadelphia October 16-21, 2009.

A Prediction Model for Future Radiologic Damage in Ankylosing Spondylitis Based On a Prospective Cohort Analysis

O'Shea, Finbar (Barry) D., Haroon, Nigil, Riarh, Reena, Inman, R.D.

# Purpose:

Spinal ankylosis is a predominant and disabling feature of ankylosing spondylitis (AS). Identifying baseline predictors of radiological progression of AS can be helpful in prognostication and treatment decisions.

# Methods:

Patients with AS (modified New York criteria), attending the Spondylitis Clinic were prospectively enrolled in this study. At the baseline visit the BASDAI, BASFI and BASMI were noted and cervical and lumbar x-rays were taken. Patients were reviewed annually and X-rays repeated every 2 years. The x-rays were scored for mSASSS by 2 independent investigators with an ICC of 0.9. X-rays were arranged sequentially and scored for mSASSS after blinding. Partial correlation coefficients were calculated after correcting for disease duration at the baseline visit. Predictors of future radiological damage were identified using a linear regression model with the last mSASSS score as the dependant variable and a regression equation was obtained for prediction. The rate of change in radiologic damage was also calculated by dividing the change in mSASSS by the time interval between the X-rays.

# Results:

Eighty seven patients (12 female), 76% were HLA-B27 positive, 64% were receiving an anti-TNF agent. Each patient had X-rays repeated at least twice with a minimum interval of 2 years. At baseline, the mean age ± SD of the patients was 36.6 ± 12.9 years and mean ± SD disease duration was 14.7 ± 9.5 years. The mean ± SD BASDAI, BASFI and BASMI were 4.8 ± 2.6, 4.1 ± 2.9 and 2.4 ± 2.0 respectively. The mean baseline and follow up mSASSS were 16.5 ± 21.8 and 18.5 ± 22.3 respectively in a mean interval of 2.7 ± 0.9 years. The mean change in mSASSS was 1.97 ± 2.9 at rate of 0.88 ± 1.6 units/year.

After correcting for disease duration, the baseline BASMI (R=0.314, p=0.04), ESR (R=0.447, p=0.001), and CRP (R=0.460, p=0.002) correlated with change in mSASSS. Baseline mSASSS, BASDAI, BASFI and age of onset did not significantly correlate with change in mSASSS. Regression analysis determined that the only two significant predictors of the final mSASSS score were baseline mSASSS and CRP. The model with mSASSS alone had and adjusted R^{2} of 0.981 (p <0.01) and the addition of CRP improved the model only minimally (R^{2} of 0.983; p <0.01). The regression equation for predicting mSASSS was 1.12 + 1.01 (baseline mSASSS) + 0.04 (baseline CRP). There was no difference in the rate of radiographic progression between patients who were or were not treated with anti-TNF agents. However there was a negative correlation between the duration of biologic intake and the rate of change in mSASSS (R=-0.297, p=0.03).

# Conclusion:

This prospective study demonstrates that baseline radiographic damage is the strongest predictor of future radiographic damage. A longer duration of anti-TNF therapy was associated with a slower rate of radiographic progression. The proposed model could have important clinical utility in defining prognosis in AS patients.

To cite this abstract, please use the following information:

O'Shea, Finbar (Barry) D., Haroon, Nigil, Riarh, Reena, Inman, R.D.; A Prediction Model for Future Radiologic Damage in Ankylosing Spondylitis Based On a Prospective Cohort Analysis [abstract]. Arthritis Rheum 2009;60 Suppl 10 :1797

DOI: 10.1002/art.26871