Background/Purpose: Systemic sclerosis (SSc) is a complex autoimmune disorder marked by vascular damage, immune dysregulation, and fibrosis. Lung involvement, particularly interstitial lung disease (ILD), carries high morbidity and mortality. Respiratory muscle weakness (RMW), though underrecognized in SSc, may contribute to pulmonary function decline independent of parenchymal involvement. Standard pulmonary function tests (PFT) measurements, such as forced vital capacity (FVC) and diffusing capacity for carbon monoxide (DLCO), may decline in patients with RMW, complicating ILD assessment. Diagnostic tools, including maximal inspiratory pressure (MIPs) and diaphragmatic ultrasound, are used to diagnose RMW. This study aims to investigate the prevalence of RMW in a SSc US population, describe the phenotype of patients with RMW, and examine the association of the proposed measurement of RMW with lung volumes and DLCO consecutive patients with SSc. We also correlate RMW with other measurements of sarcopenia in a subpopulation.

Methods: We examined PFTs measurements of RMW in 100 consecutive patients at the Jefferson Scleroderma Center at Thomas Jefferson University. Clinical phenotype, SSc-specific antibodies, MIPs, MEPs, FVC, DLCO, and the presence of ILD at HRCT were studied. We defined RMW as a MIP of less than 50%. Measurements of sarcopenia, including hand dynamometer, fast walking test, and bioimpedance, were correlated in a subgroup of patients. Chi-square was used to compare categorical variables. Spearman’s rho correlation was used to test for significant associations amongst the parameters of interest. Statistical significance was assumed at an alpha value of 0.05.

Results: From 100 SSc patients, 86 had complete PFTs data and were included for analysis. Nine patients (10.47%) were identified to have RMW at the predetermined value. In these patients, 40% displayed limited phenotype, 40% diffuse, and 10%. Sine Scleroderma versus a 25.9% of diffuse phenotype in the patients without RMW (p=0.07). Creatine Kinase value was (120.4 ±89.8 U/L) [20-458] with no difference with SSc patients with no RMW. Only one patient in the RMW group had the diagnosis of myositis. SSA/RO-52 was the most prevalent autoantibody in patients with RMW (3/9). 33.3% of the RMW-SSc patients (3/9) did not have ILD, and 44.4% (4/9) presented less than 10% of parenchymal involvement at HRCT. MIP values directly correlate with MEP (rs = 0.31, p = 0.031), and FVC (rs = 0.29, p = 0.043). No conclusive correlation was found with measurements of generalized sarcopenia.

Conclusion: RMW is prevalent in more than 10% of patients with SSc in this cohort. Diffuse phenotype and +Ro52 are more prevalent in SSc-RMW. The myositis phenotype was not commonly seen in these patients. A direct correlation between MIPs values and FVC was found. Raising awareness and identifying this phenotype opens the possibility for pharmacological and non-pharmacological therapeutic interventions. Correlation with FVC is of particular importance and requires further study since it is one of the most used values for disease progression in clinical practice and clinical research.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/respiratory-muscle-weakness-in-a-systemic-sclerosis-cohort/