A higher fat-free mass index — a measure that takes a person’s muscle mass into account — predicts better survival in patients with pulmonary fibrosis, while body mass index (BMI) does not, according to a new study.
Although researchers could not explain how body composition impacts disease progression, the findings may provide another measure to assess prognosis in clinical practice and clinical trials.
The study, “Fat-free mass index predicts survival in patients with idiopathic pulmonary fibrosis,” was published in the journal Respirology.
Since body measurements have been shown to predict progress in chronic obstructive pulmonary disease (COPD), researchers at Kindai University in Japan explored how fat-free mass index (FFMI) and BMI — which is a measure of body fat based on height and weight — correlated with various disease measures in lung fibrosis patients.
The team recruited 44 IPF patients (79.5 percent men), who underwent spirometry and measurements of carbon monoxide gas exchange in the lung. Researchers also measured exercise capacity using the 6-minute walk test, as well as anxiety, depression, and health-related quality of life.
Patients were followed for an average of 837.5 days. Of the 44 IPF patient, 21 died during the study. Death was caused by respiratory failure in 33.3% of the patients, while 14.2% died of an acute exacerbation, 4.8% of pneumonia, and 14.3% of cancer. The cause of death was unknown for the last third of the group.
The average BMI of the group was 22.8 kg/m2, but the majority of patients were in the higher ranges. The mean FFMI was 16.6 kg/m2.
A higher FFMI was correlated with better forced vital capacity (FVC; a measure of lung function), gas exchange, and exercise capacity. None of the measures correlated with the percentage of predicted FVC or gas exchange, used to indicate the severity of lung fibrosis.
FFMI and percent predicted FVC were the only factors that could predict survival, with patients who had higher FFMI living longer. Adjusting the analyses for age, gender, and BMI did not change the result.
“Taking account of not only lung function but also fat-free mass was revealed to be important in IPF practice. Methods for increasing or preserving muscle mass in IPF patients should be further investigated,” Dr. Osamu Nishiyama, lead author of the study, concluded in a news release.