Background and aims. Rheumatoid arthritis (RA) and psoriatic arthritis (PsA) are among the two most prevalent in-flammatory joint diseases. These chronic diseases are characterised by relapsing joint inflam-mation, which can result in progressive joint damage and physical impairment, particularly in the hands. Despite the relevance of hand function in daily life, its comprehensive and objective assessment is not integrated into clinical routine. The aim of this cumulative doctoral thesis was to identify and quantify hand function impairments in patients with inflammatory arthritis. Methods. This thesis includes three publications based on cross-sectional studies involving patients with RA, PsA, psoriasis (PsO), and healthy controls. A multi-modal approach was used, combining conventional hand function tests with the assessment of hand segment kinematics using an op-toelectronic motion capture system (OMS). Additionally, clinical assessments included the quantification of concurrent hand inflammation (tender/swollen joint count, ultrasonography), standard composite scores of disease activity (Disease Activity Score 28, DAS28 for RA; Dis-ease Activity in Psoriasis Arthritis, DAPSA for PsA), serology, and patient-reported outcome measures of disability and disease burden. Distinct biomechanical markers of performance and motion during various hand function tests were assessed. Linear mixed-effects models, adjusted for known confounders such as age and biological sex, were employed to analyse differences between groups and their associations with disease activity, concurrent hand inflammation and extracellular matrix (ECM) biomarkers. Results and observations. Conventional hand function tests revealed significant impairments in grip strength and fine mo-tor skills in RA and PsA patients compared to healthy controls, with more pronounced deficits observed in female patients, even in the absence of acute hand inflammation. The associations between disease activity and hand function were predominantly found in the dynamic grip strength test. OMS analysis demonstrated specific motor deficits in RA patients, particularly during the grasping phase of a fine motor skill test. Serological analysis showed that PsA and PsO patients had elevated levels of several ECM remodelling biomarkers compared to RA pa-tients and healthy controls. The strongest correlations with hand function were observed in PsO patients, suggesting that ECM dysregulation may contribute to early functional decline, even before arthritis onset. Conclusions and discussion. Hand function is consistently impaired in RA and PsA, is influenced by sex and disease activity and cannot fully be explained by acute hand inflammation. Incorporating hand function into clinical assessments provides valuable insights into disease burden and has the potential to fa-cilitate the early identification of patients at risk of developing inflammatory diseases and long-term disabilities. These findings support the importance of objectively evaluating hand function to foster a personalised approach to disease monitoring.
Coppers, Birte (Wed,) studied this question.