Measuring disease activity in giant cell arteritis: development and initial validation of a composite disease activity score

1. To develop a scoring system for the GCA Disease Activity 2. To validate the composite of the GCA Disease Activity Score (GCA-DAS). 3. To assess the GCA-DAS feasibility and effectiveness in the routine clinical setting for monitoring and assessment of treatment outcomes of GCA. The developed GCA-DAS includes acute temporal headache, visual deficit, physician global assessment of disease activity, patient global assessment of well-being, and ESR, rated on 0–10 scale. These variables have been identified as the main GCA outcome measures and criteria for improvement. Validation analyses were conducted on 124 patients and included assessment of construct validity, discriminant validity, and responsiveness to change. The GCA-DAS was found to hold face and content validity, good construct validity, satisfactory internal consistency, appropriate dimensional structure, fair discriminative validity and strong responsiveness to clinically important change over time. The devised GCA-DAS was feasible and easily recorded in standard practice. This has been supported by the parallel significant improvement in the patients’ functional ability (p < 0.001) and patient satisfaction (86.3%). The GCA-DAS was found to be a valid instrument for assessment of GCA disease activity and is potentially applicable in standard clinical care, observational studies, and clinical trials. What is already known on this topic: There is growing interest in the clinical assessment of the prognosis of Giant Cell Arteritis, however, so far, there are no valid instrument, able to facilitate regular quantitative assessment of the disease activity status. What this study adds: This study was carried out to develop and validate a composite disease activity score for Giant Cell Arteritis (GCA), the Giant Cell Arteritis Disease Activity Score (GCA-DAS). Also, to assess the feasibility of the GCA-DAS in the routine clinical setting for monitoring and assessment of treatment outcomes of GCA. How this study might affect research, practice or policy: In validation analyses, the developed GCA-DAS was found to possess good measurement properties, which makes it convenient and valid for both standard clinical practice and research settings, including clinical trials. Limitation: the next step is to do external validation in a multicentre study.