25rhk051 10.3205/25rhk051 urn:nbn:de:0183-25rhk0519 Meeting Abstract Coppers Coppers Birte B

Friedrich-Alexander-Universität Erlangen-Nürnberg & Universitätsklinikum Erlangen, Internal Medicine 3 – Rheumatology and Immunology, Deutsches Zentrum Immuntherapie, Erlangen

author Gracia Ibáñez Gracia Ibáñez Verónica V

Universitat Jaume I, Department of Mechanical Engineering and Construction, Castellón de la Plana

author Jarque-Bou Jarque-Bou Néstor J. NJ

Universitat Jaume I, Department of Mechanical Engineering and Construction, Castellón de la Plana

author Heinrich Heinrich Simon S

Friedrich-Alexander-Universität Erlangen-Nürnberg, Institute of Applied Dynamics, Erlangen

author Bayat Bayat Sara S

Friedrich-Alexander-Universität Erlangen-Nürnberg & Universitätsklinikum Erlangen, Internal Medicine 3 – Rheumatology and Immunology, Deutsches Zentrum Immuntherapie, Erlangen

author Tascilar Tascilar Koray K

Friedrich-Alexander-Universität Erlangen-Nürnberg & Universitätsklinikum Erlangen, Internal Medicine 3 – Rheumatology and Immunology, Deutsches Zentrum Immuntherapie, Erlangen

author Kleyer Kleyer Arnd A

Friedrich-Alexander-Universität Erlangen-Nürnberg & Universitätsklinikum Erlangen, Internal Medicine 3 – Rheumatology and Immunology, Deutsches Zentrum Immuntherapie, Erlangen Charité – Universitätsmedizin Berlin, Med. Klinik mit Schwerpunkt Rheumatologie und Klinische Immunologie, Berlin

author Leyendecker Leyendecker Sigrid S

Friedrich-Alexander-Universität Erlangen-Nürnberg, Institute of Applied Dynamics, Erlangen

author Schett Schett Georg G

Friedrich-Alexander-Universität Erlangen-Nürnberg & Universitätsklinikum Erlangen, Internal Medicine 3 – Rheumatology and Immunology, Deutsches Zentrum Immuntherapie, Erlangen

author Liphardt Liphardt Anna-Maria AM

Friedrich-Alexander-Universität Erlangen-Nürnberg & Universitätsklinikum Erlangen, Internal Medicine 3 – Rheumatology and Immunology, Deutsches Zentrum Immuntherapie, Erlangen

author German Medical Science GMS Publishing House

Düsseldorf

610 20250917 engl This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License. Dieser Artikel ist ein Open-Access-Artikel und steht unter den Lizenzbedingungen der Creative Commons Attribution 4.0 License (Namensnennung). M0627 051 Deutsche Gesellschaft für Rheumatologie Deutsche Gesellschaft für Orthopädische Rheumatologie 53. Kongress der Deutschen Gesellschaft für Rheumatologie (DGRh), 39. Jahrestagung der Deutschen Gesellschaft für Orthopädische Rheumatologie (DGORh) Deutscher Rheumatologiekongress 2025 Experimentelle & Translationale Rheumatologie Wiesbaden 20250917 20250920 ET.34 TextIntroduction: Rheumatoid arthritis (RA) and psoriatic arthritis (PsA) patients experience a decline in grip strength over the disease course, despite clinical remission . The underlying neuromuscular changes contributing to functional impairment remain unclear. This study aimed to identify differences in forearm muscle activity (extensor digitorum communis (EDC), flexor digitorum superficialis (FDS)), between RA, PsA patients and healthy controls (HC) during a standardized power grasp.Methods: RA (ACR/EULAR 2010) and PsA (CASPAR) patients from the Internal Medicine 3 outpatient clinics, Universitätsklinikum Erlangen (Germany), were included during routine clinical visits, and HC recruited via social networks (Ethics #357_20B). Clinical standard scores for disease activity were assessed (RA: Disease-Activity-Score 28 (DAS28); PsA: Disease Activity in PSoriatic Arthritis Score (DAPSA)). Muscle activity was recorded using electromyography (EMG) of the FDS and EDC during a standardized power grasp (Vigorimeter, KLS Martin Group, Germany, Figure 1 ). EMG amplitude parameters indicative for muscle activation (root mean square (RMS), maximum (MAX)), and waveform parameters linked to muscle effort and motor unit recruitment (new zero crossing (NZC), enhanced wavelength (EWL)) were calculated and compared between groups (linear mixed-effect models, stratified by sex, adjusted for age, hand dominance; participant ID as random intercept term).Results: 187 participants were included (HC: n=43, 22/21 f/m, age 54±16; RA: n=69, 47/22 f/m, age 53±14; PsA: n=75, 38/37 f/m, age 54±14). Despite low disease activity, female PsA patients showed reduced grip strength and lower EWL in FDS and EDC compared to HC and RA. Female RA patients had higher RMS compared to PsA and lower grip strength than HC (Table 1 ). No significant differences were found in male participants (all p>0.05).Conclusion: These findings align with previous research showing increased RMS values in functional tasks in female RA patients , suggesting greater muscle activation to compensate for functional impairments, whereas PsA patients show lower muscle effort (EWL), reflecting limited strength output. The observed deficits in hand function in patients who are mostly in clinical remission are likely due to disease-related neurophysiological changes. EMG analysis serves as a valuable tool to detect these adaptations of muscle function and highlights different compensatory mechanisms in female PsA and RA patients. Rydholm M Book C Wikström I Jacobsson L Turesson C Course of Grip Force Impairment in Patients With Early Rheumatoid Arthritis Over the First Five Years After Diagnosis 2018 Arthritis Care Res (Hoboken) 491-8 Rydholm M, Book C, Wikström I, Jacobsson L, Turesson C. Course of Grip Force Impairment in Patients With Early Rheumatoid Arthritis Over the First Five Years After Diagnosis. Arthritis Care Res (Hoboken). 2018 Apr;70(4):491-8. DOI: 10.1002/acr.23318 http://dx.doi.org/10.1002/acr.23318 Jarque-Bou NJ Vergara M Sancho-Bru JL Does Exerting Grasps Involve a Finite Set of Muscle Patterns? A Study of Intra- and Intersubject Variability of Forearm sEMG Signals in Seven Grasp Types 2024 IEEE Trans Neural Syst Rehabil Eng 1505-14 Jarque-Bou NJ, Vergara M, Sancho-Bru JL. Does Exerting Grasps Involve a Finite Set of Muscle Patterns? A Study of Intra- and Intersubject Variability of Forearm sEMG Signals in Seven Grasp Types. IEEE Trans Neural Syst Rehabil Eng. 2024;32:1505-14. DOI: 10.1109/TNSRE.2024.3383156 http://dx.doi.org/10.1109/TNSRE.2024.3383156 Brorsson S Nilsdotter A Thorstensson C Bremander A Differences in muscle activity during hand-dexterity tasks between women with arthritis and a healthy reference group 2014 BMC Musculoskelet Disord 154 Brorsson S, Nilsdotter A, Thorstensson C, Bremander A. Differences in muscle activity during hand-dexterity tasks between women with arthritis and a healthy reference group. BMC Musculoskelet Disord. 2014 May 15;15:154. DOI: 10.1186/1471-2474-15-154 http://dx.doi.org/10.1186/1471-2474-15-154 11

Table 1: Electromyography parameters and clinical disease activity by group.

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1 1 Figure 1: Power grasp in the motion capture set-up.

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