Background Monitoring disease activity in patients with inflammatory arthritis is essential for effective treatment. While the health assessment questionnaire (HAQ) is commonly used to assess physical function, additional functional tests, such as isometric grip strength and the Moberg Pick-Up-Test (MPUT), provide objective measures for hand function and allow assessing hand function across different diseases (1). It remains unclear to date, if measured hand function is already reflected by the HAQ, as the most widely used patient reported outcome measure of physical function in arthritis.
Objectives To estimate the proportion of hand function and grip strength variability explained by HAQ, patient-reported hand function, and between-person variation in patients with inflammatory arthritis and non-arthritic controls.
Methods Patients with rheumatoid arthritis (RA), psoriatic arthritis (PsA), psoriasis without PsA (PsO) and healthy controls (HC) were investigated. Subject characteristics (age, sex, disease) and HAQ were recorded. Hand function was assessed by vigorimetric grip strength, MPUT, and a patient-reported tool (Michigan Hand Questionnaire, MHQ). Mixed pure-random-effect linear regression models were used to estimate the proportion of variance in measured hand function or grip strength explained by subject characteristics (age, hand dominance, sex, reported hand function, disease group).
Results 299 subjects were tested, 101 with RA (Age: 59.1±13.3 years, BMI: 27.2±5 kg/m2, HAQ-DI score: 0.9±06), 92 with PsA (Age: 58.8±11.6 years, BMI: 29±6.1kg/m2, HAQ-DI score: 0.6±0.7) and 106 non-arthritic controls (51 with Pso (Age: 47.3±14.1 years, BMI: 29.8±7.3 kg/m2, HAQ-DI score: 0.4±06) and 55 HC (Age: 54.6±16.5 years, BMI: 25.2±3.3 kg/m2, HAQ-DI score: 0.1±0.2). Overall variation of MPUT is mostly accounted for by between-person variation (43.1%), followed by HAQ (20.3%) and MHQ (20.2%) (Figure 1A). Overall variation in grip strength is mostly accounted for by sex (59.8%), between-person variation (21.1%) and HAQ (11.3%) (Figure 1B). Overall variation in MHQ is mostly accounted for by HAQ (59.2%) and residual variation (28.3%). Study group specific result are summarized in Table 1.
Conclusion While the variance variation in grip strength is mainly explained by sex and between-person variation for all subject groups, the proportions of explained variance for measured hand function is not similar between diseases. In all groups > 50% of the variation in measured hand function remains unexplained by the variables used. Especially in arthritis patients, HAQ explained less than 25% of the variance in measured hand function. Grip-strength can be considered a poor surrogate for hand function in this context due to its large gender dependence. The explainability of MHQ variation largely by HAQ indicates that it has limited potential to provide further information beyond overall functional impairment. In contrast, the large between-person variation in MPUT likely indicates unexplored movement patterns of hand motion that may be further dissected using sensor-based analyses (2) and can help identify movement components a potential for an in-depth assessment of subtle hand-function alterations in inflammatory arthritis.
References Liphardt AM et al. ACR Open Rheumatol 2020, 2, 734-740. 2. Phutane U et al. Sensors (Basel) 2021, 21.
Acknowledgements This study was supported by the German Research Council (SFB 1483 – Project-ID 442419336, INST 90 / 985-1 FUGG, FOR2438/2886; SFB1181), the German Ministry of Science and Education (project MASCARA), the European Union (H2020 GA 810316 - 4D-Nanoscope European Research Council Synergy Project) and Novartis Germany GmbH.
Disclosure of Interests None declared
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