O016 - SIX-YEAR VALIDATION AND CROSS-POPULATION TRANSPORTABILITY OF AN ANTHROPOMETRIC APPENDICULAR LEAN MASS MODEL IN RHEUMATOID ARTHRITIS

O016

SIX-YEAR VALIDATION AND CROSS-POPULATION TRANSPORTABILITY OF AN ANTHROPOMETRIC APPENDICULAR LEAN MASS MODEL IN RHEUMATOID ARTHRITIS

Y. Matsumoto^1,*, Y. Sugioka², M. Tada³, T. Okano², K. Mamoto⁴, K. Inui⁵, D. Habu¹, T. Koike⁶

¹Department of Nutrition, Graduate School of Human Life and Ecology, Osaka Metropolitan University, ²Center for Senile Degenerative Disorders, Osaka Metropolitan University Medical School, ³Department of Orthopaedic Surgery, Osaka City General Hospital, ⁴Department of Orthopaedic Surgery, Osaka Metropolitan University Medical School, ⁵Department of Orthopaedic Surgery, Osaka Saiseikai Nakatsu Hospital, Osaka, ⁶Search Institute for Bone and Arthritis Disease, Shirahama Foundation for Health and Welfare, Shirahama, Japan

Rationale: Accurate assessment of appendicular lean mass (ALM) is central to sarcopenia diagnosis and phenotypic evaluation within the Global Leadership Initiative on Malnutrition (GLIM). Dual-energy X-ray absorptiometry (DXA) is the reference standard but is not routinely accessible. No anthropometric ALM equation has been developed and longitudinally validated specifically in rheumatoid arthritis (RA), a chronic inflammatory disease associated with muscle loss. We developed an RA-specific ALM prediction model and examined its long-term stability and transportability.

Methods: An ALM model using sex, body weight, and waist circumference was developed in 2010 from DXA data of 208 RA patients. Temporal validation was conducted in the original RA cohort at 3 years (2013) and 6 years (2017) using repeated DXA-based ALM measurements, without refitting coefficients. Performance was assessed by coefficient of determination (R²), root mean square error (RMSE), calibration slope, and Lin’s concordance correlation coefficient (CCC). Discrimination for low skeletal muscle index (SMI) was evaluated using the area under the receiver operating characteristic curve (AUC). Transportability was tested by applying the RA-derived model to 184 age- and sex-matched controls assessed in 2017.

Results: In RA patients, performance remained stable across follow-up (2013: R²=0.77, RMSE=1.81 kg, CCC=0.87; 2017: R²=0.82, RMSE=1.45 kg, CCC=0.90), with calibration slopes near 1. AUCs for low SMI were 0.73 (2013) and 0.71 (2017). In controls in 2017, agreement was strong (R²=0.89, CCC=0.88) with good discrimination for low SMI (AUC=0.84).

Conclusion: This RA-derived anthropometric ALM model showed sustained 6-year validity and robust cross-population performance, supporting its clinical applicability for sarcopenia and GLIM-related muscle mass assessment when DXA is unavailable.

Disclosure of Interest: Y. Matsumoto: None declared, Y. Sugioka: None declared, M. Tada: None declared, T. Okano Grant / Research Support from: AbbVie, Eisai, Mitsubishi Tanabe Pharma Corporation and Nipponkayaku, Speakers Bureau of: AbbVie, Asahikasei, Astellas Pharma Inc, Ayumi Pharmaceutical, Bristol-Myers Squibb, Chugai Pharmaceutical, Daiichi Sankyo, Eisai, Janssen, Lilly, Mitsubishi Tanabe Pharma Corporation, Novartis Pharma, Ono Pharmaceutical, Pfizer, Sanofi, Takeda Pharmaceutical, Teijin Pharma and UCB, K. Mamoto: None declared, K. Inui Grant / Research Support from: Janssen Pharmaceutical K.K., Astellas Pharma Inc., Sanofi K.K., Abbvie GK, Takeda Pharmaceutical Co. Ltd., QOL RD Co. Ltd., Mitsubishi Tanabe Pharma, Ono Pharmaceutical Co. Ltd., and Eisai Co. Ltd., Speakers Bureau of: Daiichi Sankyo Co. Ltd., Mitsubishi Tanabe Pharma, Janssen Pharmaceutical K.K., Astellas Pharma Inc., Takeda Pharmaceutical Co. Ltd., Ono Pharmaceutical Co. Ltd., Abbvie GK, Pfizer Inc., Eisai Co. Ltd., and Chugai Pharmaceutical Co. Ltd., D. Habu: None declared, T. Koike Grant / Research Support from: AbbVie, Astellas Pharma Inc., Bristol-Myers Squibb, Chugai Pharmaceutical, Eisai, Janssen, Lilly, Mitsubishi Tanabe Pharma Corporation, MSD, Ono Pharmaceutical, Pfizer, Roche, Takeda Pharmaceutical, Teijin Pharma, and UCB, Speakers Bureau of: AbbVie, Astellas Pharma Inc., Bristol-Myers Squibb, Chugai Pharmaceutical, Eisai, Janssen, Lilly, Mitsubishi Tanabe Pharma Corporation, MSD, Ono Pharmaceutical, Pfizer, Roche, Takeda Pharmaceutical, Teijin Pharma, and UCB