Muscle Function in Moderate to Severe Asthma: Association With Clinical Outcomes and Inflammatory Markers

Abstract

Background: Patients with severe asthma have been shown to have low muscle mass, but the clinical consequences are unknown.

Objective: In a clinical cohort of patients with moderate to severe asthma, we aimed to assess muscle mass and strength and their relation with functional and clinical outcomes, as well as with systemic inflammatory markers.

Methods: Muscle mass and strength were assessed by the fat-free mass index (FFMI), creatinine excretion in a 24-hour urine sample, and handgrip strength test. Functional outcomes included pulmonary function tests and the 6-minute walking distance, whereas clinical outcomes were assessed with questionnaires on asthma control, quality of life, and health care use. Associations of muscle mass and strength with asthma outcomes were assessed with multivariable regression analyses.

Results: A total of 114 patients participated (36% male; mean age, 51.9 ± 14.4 years; body mass index, 27.7 ± 5.7 kg/m²). According to predefined criteria, 16% had a low FFMI and 8% a low urinary creatinine excretion, which did not differ between categories of asthma severity. Both lower FFMI and urinary creatinine excretion were associated with lower values of FEV₁ and 6-minute walking distance, whereas a lower handgrip strength was related to worse asthma control, poorer quality of life, and a higher probability of emergency visits (all P < .05). Except for higher leukocytes in relation to lower FFMI, we did not find associations between systemic inflammatory markers and muscle function.

Conclusions: This study demonstrates that low muscle mass is prevalent in patients with moderate to severe asthma and, along with low muscle strength, is associated with poorer clinical and functional outcomes. Our results encourage longitudinal studies into muscle function as a potential target for treatment to improve asthma outcomes.

Keywords: Airway obstruction; Asthma control; Exercise capacity; Health care use; Muscle function; Quality of life; Severe asthma; Systemic inflammation.