Corticosteroids are associated with reduced skeletal muscle function in interstitial lung disease patients with mild dyspnea.

Background: Interstitial lung diseases (ILDs) patients receiving steroid treatment tend to be immobilized by dyspnea and muscle weakness as the disease progresses. We therefore expected that steroid treatment for ILDs would have a greater effect on muscle function under severe dyspnea. To test this hypothesis, we evaluated whether the effect of corticosteroid treatment on peripheral muscle force and exercise capacity varied according to patients' dyspnea severity.
Methods: In this retrospective cross-sectional study of 87 ILD patients enrolled between 2008 and 2017, quadriceps force (QF), handgrip force (HF), and 6-min walk distance (6 MWD) were compared between a low (grades 0-2) and a high (grades 3-4) modified-Medical Research Council (mMRC) dyspnea scale score group.
Results: In patients with lower levels of dyspnea, corticosteroid treatments were associated with lower QF and HF (20.0 vs. 30.0 kgf, p = 0.01; 22.5 vs. 28.4 kgf, p = 0.03, respectively) values; however, no significant differences were observed between the corticosteroid and control subgroups in the high mMRC group (QF: 18.5 vs. 17.3 kgf, p = 0.64; HF: 21.0 vs. 17.1 kgf, p = 0.24, respectively). Analysis of covariance indicated that both corticosteroid treatment and mMRC dyspnea scale interacted with QF, HF, and 6 MWD. The effects of the corticosteroid treatment varied according to the level of dyspnea (interaction β = 7.52, p = 0.034; interaction β = 8.78, p = 0.048; interaction β = 131.08, p < 0.001).
Conclusions: Muscle weakness and exercise capacity in ILD patients in the low mMRC group were associated with corticosteroid treatment.
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