Respiratory Muscle Strength in Rheumatoid Arthritis.

Rheumatoid arthritis (RA) is known to affect the musculoskeletal system and, consequently, may lead to sarcopenia, but the role of respiratory muscle involvement in RA patients is unclear. This prospective, exploratory, single-center, matched-pair analysis study was designed to compare respiratory muscle strength and handgrip strength in RA patients and controls. RA patients with low disease activity as estimated from the Disease Activity Score 28 (2.3 ± 1.2) and without signs of interstitial lung disease ( = 36, 72% female, 28% smoker, mean age 48 + 15 years, mean forced vital capacity 3.9 ± 1.0 L, 98% ± 11% predicted) and control subjects ( = 36, 72% female, 11% smoker, mean age 48 + 14 years, mean forced vital capacity 4.1 ± 1.1 L, 98% ± 16% predicted) were well balanced. Maximal inspiratory mouth pressure (PImax, primary endpoint) tended to be lower in RA patients, but this was statistically not significant (-0.9 kPa; 95%CI = -2.11/0.32). However, RA patients more frequently had PImax values below the lower limit of normal (OR 1.74 kPa; 95% CI 0.65/4.77). RA patients had lower handgrip strength (-5.97 kg; 95%CI = -9.43/-2.50). In addition, PImax was correlated to handgrip strength both in RA patients (R = 0.51, = 0.0017) and controls (R = 0.48, = 0.0029) and to the 6-minute walking distance (RA-patients: R = 0.30, = 0.075; controls: R = 0.52, = 0.0012). Even though the primary endpoint has not been reached, an impairment of respiratory muscle strength in RA cannot be excluded at least in a subset of patients. Further studies also involving RA patients with more disease activity are needed.