From the Journals

Muscle weakness predicts poor outcomes in asthma patients



Lower muscle mass was significantly associated with more airway obstruction and reduced functional exercise capacity in adults with asthma, based on data from 114 individuals.

Previous studies have shown reduced muscle mass in asthma patients, but the impact on clinical and functional outcomes has not been well studied, wrote Edith Visser, MSc, of Medical Centre Leeuwarden (the Netherlands) and colleagues.

“Many asthma patients, especially those with severe disease, report exercise intolerance and limitations in daily activities, severely affecting their quality of life,” they said. Research into the clinical consequences of low muscle mass and low muscle strength for patients with asthma and the role of inflammation could make muscle function a potential treatment target for those with asthma, they said.

In a study published in the Journal of Allergy and Clinical Immunology: In Practice, the researchers recruited 114 consecutive adults aged 18 years and older with a diagnosis of moderate to severe asthma who were seen at a single center between Jun. 2019 and Oct. 2022. The mean age of the patients was 51.9 years, 36% were men, 70% were overweight or obese, and 34 were diagnosed with severe asthma.

Participants underwent clinical, functional, and laboratory assessments at one or two visits within a 2-week period. Assessment tools included the Asthma Quality of Life Questionnaire (AQLQ), the Asthma Control Questionnaire (ACQ-6), a questionnaire on health care use (HCU), and the ‘short questionnaire to assess health-enhancing physical activity’ (SQUASH).

Functional activity was based on the 6-minute walking distance (6MWD), and lung function tests included spirometry and fractional inhaled nitric oxide (FeNO). Muscle mass was based on fat-free mass index (FFMI) and urinary creatinine excretion rate (CER). Muscle strength was measured using hand-grip strength (HGS).

The researchers examined levels of muscle mass and strength and their relation to functional and clinical outcomes.

Overall, the mean measures of muscle mass and strength were higher in males, who had average FFMI, CER, and HGS measures of 20.1 kg/m2, 15.3 mmol/day, and 48.8 kg, respectively. These measures in women were 17.3 kg/m2, 10.8 mmol/day, and 29.3 kg, respectively.

After adjusting for confounding factors, patients in the lowest tertile for muscle mass based on FFMI had significantly more severe asthma based on postbronchodilator forced expiratory volume in 1 second and FEV1/forced vital capacity, as well as lower functional exercise capacity based on the 6MWD compared to those in the highest tertile. A similar association appeared between CER and FEV1, but not FEV1/FVC.

However, no significant associations appeared between the muscle mass measures of FFMI or CER and scores on the ACQ, AQLQ, emergency department visits, or asthma exacerbations, the researchers noted.

No relationship appeared between muscle strength and functional outcomes. However, patients in the lowest tertile of HGS had worse asthma control, worse quality of life, and a higher probability of at least one visit to the emergency department compared to patients in the highest HGS tertile.

Higher leukocyte levels were significantly associated with lower muscle mass after adjusting for age, sex, weight, and physical activity, but no other inflammatory markers were significantly associated with FFMI.

The association between lower muscle strength and poorer asthma control, lower quality of life, and greater odds of emergency department visits reflect findings from previous studies, the researchers said. The mechanisms behind the loss of muscle strength in asthma remain unclear, but physical inactivity and daily oral corticosteroid use may play a role, they added.

The study findings were limited by the cross-sectional design and the possibility that muscle weakness may instead stem from reduced physical activity associated with poor lung function and asthma control, the researchers noted. Other limitations included the potential overestimation of FFMI and the lack of statistical power to show a relationship between FFMI and emergency department visits and asthma exacerbations, they said.

However, the current study is the first known to explore the relationship between lower muscle mass and strength and a range of both functional and clinical outcomes in patients with moderate to severe asthma, they said.

“Our findings encourage longitudinal studies into muscle function as a potential target for treatment to improve asthma outcomes,” they concluded.

The study was supported by unrestricted grants from Medical Centre Leeuwarden research fund. Ms. Visser had no financial conflicts to disclose.

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