Disease activity in patients with idiopathic inflammatory myopathy according to time since diagnosis and positivity to antisynthetase autoantibodies: data from the Myo-Spain registry

Abstract Objective To evaluate the main outcomes of disease activity and their association with other measures of activity, damage, and quality of life in patients with idiopathic inflammatory myopathy (IIM) according to time since diagnosis and positivity to antisynthetase autoantibodies (ASAs). Methods Cross-sectional multicenter study within the Spanish Myo-Spain registry. Cases were classified as incident (≤ 12 months since diagnosis) and prevalent. The main outcomes of disease activity were the Myositis Disease Activity Assessment visual analogue scale (MYOACT), the Manual Muscle Test 8 (MMT-8), physician global activity (PhGA), and extramuscular activity. Other measures of activity, damage, and quality of life included patient global disease activity, MYOACT muscular, creatine phosphokinase, Health Assessment Questionnaire, physician and patient global damage, global damage of the Myositis Damage Index, and the 12-item Short-Form Health Survey (SF-12). We analyzed associations using a multivariate generalized linear model and a simple linear regression model. Results A total of 554 patients with different diagnostic subgroups of IIM were included (136 incident and 418 prevalent cases), with 215 ASA-positive patients (58 incident and 157 prevalent cases). All measures of disease activity were higher in the incident cases (p