Assessing Respiratory Muscle Strength in Patients with Rheumatoid Arthritis: An Exploratory Study

<bold>BACKGROUND:</bold> Pulmonary manifestations such as interstitial lung disease are well recognized in patients with rheumatoid arthritis (RA). However, the role of respiratory muscle involvement is unclear. <bold>Methods:</bold> This prospective, exploratory, single-center, matched-pair analysis study was designed to compare the primary endpoint of maximal peak inspiratory pressure (PImax) and spirometric and bodyplethymographic secondary endpoints between RA patients and controls. Multiple linear regression was used to analyze the endpoints between these two groups, adjusting for age, sex, and body mass index (BMI). <bold>RESULTS:</bold> The mean age in the RA (N=36, 72%female) and in the control group (N=36, 72%female) was 48+15 and 48+14 years, respectively. Body weight and height were well balanced. Among RA patients, 31% (n = 11) were in active disease and 69% (n = 25) were in remission. RA had no independent effect on PImax (−0.9 kPa; 95%CI = -2.11/0.32). The negative effect of RA on PImax can be inferred as a clinical trend, reflected by accumulation of values below the lower limit (OR 1.74 kPa; 95% CI 0.65/4.77). Associations were observed between lower PImax and lower 6-minute walk distance (R=0.3) and between lower handgrip strength and lower PImax (R=0.51). There was a negative effect of hand strength loss in RA patients (−5.97 kg; 95%CI = -9.43/-2.50). The other secondary endpoints showed did not show significant differences. <bold>DISCUSSION:</bold> The study showed a clinically relevant trend towards reduced PImax in RA patients, while no significant negative effect on pulmonary function parameters was observed. Further and larger studies are needed to demonstrate clinical significance.