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BackgroundThe MSK components of the BILAG and SLEDAI have limited sensitivity, specificity and responsiveness.ObjectivesTo develop a better disease activity tool for MSK lupus.Methods“LAMDA” was derived using data from the multicentre USEFUL study (PMID:33792659); 133 patients with inflammatory MSK pain received intramuscular depomedrone then were assessed for 66/68 SJC/TJC, BILAG-2004, SLEDAI-2K, physician MSK-VAS, inflammatory markers, patient pain and disease-activity-VAS and MSK-ultrasound. Baseline variables were modelled against US using penalized (Lasso) regression. For validation we evaluated: (i) responsiveness at week 6 in USEFUL and (ii) association with quality of life and treatment decision in an independent study (n=100).ResultsLAMDA was a composite of SJC, patient-MSK-pain-VAS, physician-MSK-disease-activity-VAS and ESR ranging from 0 to 26.5. Response effect size was greater for the LAMDA (0.37) than the BILAG-MSK (0.31), SLEDAI-MSK (0.27) and total US score (0.33). With active US at baseline, LAMDA’s effect size was 0.42.In the validation study LAMDA score correlated with better physical function (R = -0.49, pConclusionLAMDA is a continuous disease activity instrument for MSK lupus that is sensitive to imaging-synovitis without swelling, more responsive than other instruments and correlates with quality of life and treatment decision. LAMDA may improve the ability of clinicians to monitor and treat MSK lupus, and determine the efficacy of therapies in clinical trials.AcknowledgementsFunding: Lupus UK and NIHRDisclosure of InterestsKhaled Mahmoud: None declared, Ahmed Zayat: None declared, Md Yuzaiful Md Yusof: None declared, Lee-Suan Teh: None declared, Shah Khan: None declared, Chee-Seng Yee: None declared, David D’Cruz: None declared, Nora Ng: None declared, David Isenberg: None declared, Coziana Ciurtin: None declared, Philip G Conaghan: None declared, Paul Emery: None declared, Christopher John Edwards: None declared, Elizabeth Hensor: None declared, Edward Vital Speakers bureau: GSK, AstraZeneca, Consultant of: GSK, AstraZeneca, Roche, Aurinia, Lilly, ILTOO, Novartis, Grant/research support from: AstraZeneca, Sandoz