BackgroundThere are different measures and tools validated to evaluate disease activity and damage in idiopathic inflammatory myopathies (IIM). Disease activity and damage in patients with early diagnosis is not still well defined.ObjectivesTo analyze disease activity outcomes and their association with damage in IIM differentiating between incident and prevalent cases.MethodsMulticenter cross-sectional study of a cohort of patients included in the Spanish Registry of patients with IIM (Myo-Spain)(1). Patients were classified as incident cohort (time between diagnosis and study initiation ≤ 12 months) or prevalent cohort (> 12 months). Activity and damage data were collected at the initial visit. Differences between both groups were tested by Chi-square, Student’s t and Mann-Whitney tests. Spearman’s correlation coefficients (Rho) were used to analyze correlations between disease activity and damage measures (weak ≥ 0.2 - <0.3; moderate ≥ 0.3 <0.7; strong ≥ 0.7).ResultsWe included 139 (67.63% women) and 417 patients (74.34% women) with a mean age at diagnosis of 54 and 48 years in the incident and prevalent cohort, respectively. Patients in the incident cohort had significantly higher disease activity measures: myositis disease activity assessment visual analogue scale (MYOACT) total, extramuscular activity of MYOACT, physician global activity (PhGA), patient global activity (PGA), manual muscle testing (MMT)8, CK, and HAQ (p < 0.001).The organ systems with the bigger differences between the incident and the prevalent cohort were skin and constitutional (p<0.001). No significant differences were found respect to physician global damage (PhGD), patient global damage (PGD) and myositis damage index (MDI), between both cohorts (p > 0.2). Correlations between disease activity and damage measures are showed in the Table 1. The main differences found between both cohorts were the correlations of PhGA, CK, PGD and MDI with other measures of disease activity.Table 1.Correlations between disease activity and damage measuresIncident cohortPrevalent cohortMYOACT totalExtramuscular activity of MYOACTPhGAMMT- 8MYOACT totalExtramuscular activity of MYOACTPhGAMMT- 8Extramuscular activity of MYOACTRho0.7610.673-0.1660.77710.764-0.214P-value<0.001<0.001<0.0010.065<0.001<0.001<0.001<0.001PhGARho0.8230.6731-0.50.7790.7641-0.301P-value<0.001<0.001<0.001<0.001<0.001<0.001<0.001<0.001PGARho0.6670.5440.679-0.4340.5850.5280.623-0.345P-value<0.001<0.001<0.001<0.001<0.001<0.001<0.001<0.001MMT-8Rho-0.471-0.166-0.51-0.383-0.214-0.3011P-value<0.0010.065<0.001<0.001<0.001<0.001<0.001<0.001CKRho0.221-0.0860.234-0.4380.07-0.0240.112-0.11P-value0.0140.3510.008<0.0010.1780.6480.0290.034HAQRho0.4860.3380.528-0.490.3860.2480.384-0.505P-value<0.001<0.001<0.001<0.001<0.001<0.001<0.001<0.001PhGDRho0.3670.310.448-0.3050.5730.4920.598-0.334P-value<0.0010.001<0.0010.001<0.001<0.001<0.001<0.001PGDRho0.2930.1630.354-0.2950.4680.4080.476-0.347P-value0.0030.102<0.0010.002<0.001<0.001<0.001<0.001MDIRho0.3980.2790.388-0.2320.5790.4770.545-0.343P-value<0.0010.006<0.0010.026<0.001<0.001<0.001<0.001Myositis disease activity assessment visual analogue scale (MYOACT), physician global activity (PhGA), patient globalactivity (PGA), manual muscle testing (MMT)8, health assessment questionnaire (HAQ), physician global damage(PhGD), patient global damage (PGD), myositis damage index (MDI).ConclusionIncident cases had higher disease activity. In those in whom damage was detected, no differences were found in damage measures with prevalent cases. The correlation between the different measures of activity and damage was slightly better in prevalent patients.References[1]Cobo-Ibáñez T, et al. Myo-Spain: Spanish Registry of patients with idiopathic inflammatory myopathy. Methodology. Reumatol Clin (Engl Ed). 2021 Aug 13:S2173-5743(21)00156-8.AcknowledgementsTo Nuria Montero for her contribution to data monitoring, and Francisco Javier Prado-Galbarro for his contribution to data analysis.Disclosure of InterestsNone declared