Background/Purpose: To compare the impact of psoriatic arthritis (PsA) and rheumatoid arthritis (RA) on objective and subjective parameters of hand function.

Methods: Hand function was assessed by (i) vigorimetric grip strength, (ii) Moberg picking up test (MPUT) and (iii) self-reported hand function (Michigan Hand Questionnaire, MHQ). Mixed effects linear regression models were used to test the relation of hand function with age, sex and disease group.

Results: 299 subjects were tested, 101 with RA (Age: 59.1 ± 13.3 years, BMI: 27.2 ± 5 kg/m²), 92 with PsA (Age: 58.8 ± 11.6 years, BMI: 29 ± 6.1kg/m²) and 106 non-arthritic controls (51 with Pso (Age: 47.3 ± 14.1 years, BMI: 29.8 ± 7.3 kg/m²) and 55 healthy controls (HC, Age: 54.6 ± 16.5 years, BMI: 25.2 ± 3.3 kg/m²). Grip strength as a measure of muscle force (lbf) was lowest in RA patients (57.9(31)), followed by PsA (72.8(34.7)), Pso (80.4(34.1) and HC (84.1(24.9)) respectively. MPUT (seconds) of the dominant hand was best in HC (11.5(2.3)), followed by Pso patients (14.7(4.6)), PsA (16.4(8.5)) and RA (18.2(21.6)). Group means for self-reported hand function score by MHQ ranged between 77.2 (HC) and 63.8 for RA patients. Regression analysis showed that grip strength was affected by sex, age and disease group (p< 0.001 for all) with higher values but also greater decline with increasing age in male individuals (Figure 1A). PsA, RA and unexpectedly also psoriasis lowered grip strength in females, while in males only modest disease-related reductions of grip strength were observed. Fine motor skills as assessed by MPUT remained remarkably stable in healthy subjects during age. However, they significantly dropped with age in RA, PsA and interestingly also in psoriasis patients (p < 0.001 for the interaction of MPUT with age and disease Group, Figure 1B). Self-reported hand function was assessed by MHQ. Regression analysis showed that MHQ is significantly affected by age, disease status and hand dominance (p < 0.001 for all). The effect of disease on the MHQ increased with age and was more pronounced in females. Estimated marginal mean MHQ incrementally deviated from controls in PsA and psoriasis with increasing age, whereas in RA self-reported hand function was already low in younger subjects (Figure 1C).

Conclusion: In conclusion, the impact of PsA on hand function is similar to RA and affects muscular force, fine motor skills and self-perception of hand function. The burden of disease on hand function increased with age and affects both sexes and both hands. In addition, hand function is impaired already in psoriasis patients suggesting intrinsic functional musculoskeletal alterations in psoriatic disease, which occur independently from PsA.

Figure 1: Estimated marginal means with multiplicity-adjusted 95% confidence intervals for psoriatic arthritis patients (PsA), rheumatoid arthritis patients (RA), psoriasis patients (PsO) and healthy controls (HC) at ages 35, 55 and 75 by gender and dominant hand.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/similar-impact-of-psoriatic-arthritis-and-rheumatoid-arthritis-on-objective-and-subjective-parameters-of-hand-function/