Pos0734 analysis of improvement in giant cell arteritis: defining thresholds for gca-response

Background The creation of instruments for the structured assessment of disease activity has facilitated the effective use of DMARDs to control disease activity in patients with inflammatory arthritis. Composite measures for Giant Cell Arteritis (GCA) incorporating several key clinical and laboratory variables which allow for a standardized quantitative assessment of GCA disease activity has been recently introduced. These assessment tools for measuring disease activity are of particular benefit in helping to achieve therapeutic goals in patients with GCA, including amelioration of the symptoms and signs of active disease, and the consequent avoidance of functional impairment and restoration of physical function. Objectives To identify the preliminary definition of improvement in GCA and the higher thresholds for improvement reflecting significant and major improvement as well as remission. Methods In developing criterion for improvement of individual GCA patients, consideration was restricted to the 6 variables identified as outcome measures: severity of headache (0-100), acute visual deficit (0-100), functional disability (0-3), Patient Global Assessment (0-100), Physician global assessment (0-100), ESR and CRP levels. For each variable, the value at baseline were compared with the value at 4-weeks and 12-weeks of treatment to determine the degree of improvement or deterioration that occurred. The percentage of improvement was calculated directly for each of the 6 variables in 51 patients. Using the 6 variables, preliminary analysis was performed to determine the percentage of improvement. Preliminary definition of improvement required >x% improvement in >y of the 6 variables, where “x” was set at 20%, 30%, 40%, 50%, 70%, 90% and 100%, and “y” was set at 2,3,4,5, or 6 variables. To assess the discriminating power of high response percentages (70%, 90% and 100%) the percentage of improvement in the headache severity (as the main outcome measure reflecting the disease activity status) was compared to the change of the rest of the core set measures. The individual improvement criterion identified was then applied prospectively to a cohort of 25 patients diagnosed to have GCA and starting their therapy. Results A definition of >50% improvement in 4 or more variables produced the largest difference between patient’s assessment at 4-weeks and 12-weeks in comparison to the baseline. Sharpening the cut-offs to 70% or 90% means that the patient should nearly or completely reach a status of remission in order to fulfil such an impressive improvement criterion. Reaching 100% means that the patient has achieved remission. Outcome of the prospective study revealed that 100% of the patients achieved 50% GCA response. Assessing the higher response rates, revealed that 10% of the patients achieved 70%, 30% achieved 90% whereas 60% achieved 100%. Conclusion Core sets of valid outcome measures have been defined. GCA response criteria have been developed and showed comparable validity. The 70% (significant improvement), 90% (major improvement) and 100% (remission) GCA improvement criteria showed good discriminating capacity though less than the 50% criteria. GCA response can be used in standard clinical practice to identify disease activity status and response to therapy. Calculation of GCA-N index would be the next step to attain a continuous variable rather than at arbitrary 20%, 50%, and 70% levels. A second advantage is that a continuous index can include recognition of possible deterioration in addition to improvement. REFERENCES: NIL. Acknowledgements: NIL. Disclosure of Interests None Declared.