Muscle stiffness in rheumatoid arthritis is not altered or associated with muscle weakness: A shear wave elastography study

Objectives: To investigate muscle stiffness and strength in rheumatoid arthritis patients compared to healthy controls. Methods: A sample of 80 RA patients from three discrete groups: 1 - newly diagnosed treatment-naive RA (n = 29), 2 - active RA for at least 1 year (n = 18) and 3 - in remission RA for at least 1 year (n = 33), was compared to 40 healthy controls. Shear wave velocity (SWV) was measured using shear wave elastography as a surrogate for tissue stiffness in multiple muscles. All participants performed isometric grip strength, timed get-up-and-go test, 30-s chair stand test and isokinetic knee extension/flexion (60 degrees/s). The difference in SWV amongst the groups was tested using one-way ANOVA, and the correlation between SWV and muscle strength results were calculated using Pearson's coefficients. Results: The mean age +/- SD was 61.2 +/- 12.8 for RA patients and 61.5 +/- 10.5 years for controls. SWV was not significantly different amongst the groups on all muscles (p > .05). In comparison to controls, the new and active RA groups showed a significantly lower isokinetic strength by -29% (p = .013) and -28% (p = .040), fewer chair stands by -28% (p = .001) and -44% (p < .001), longer walking times by -25% (p = .025) and -30% (p = .001), respectively, and weaker grip strength by -45% for both (p < .001). The muscle strength in the remission RA groups was not significantly lower, except in the isokinetic knee strength (-21%; p = .027). The correlations between SWE and the muscle assessment results were weak and insignificant (r < 0.30; p > .05). Conclusion: Significant muscle weakness was demonstrated in patients with RA disease. However, muscle stiffness was normal and not associated with muscle strength.