Measuring the loss of skeletal muscle mass in the thoracic area using computed tomography (CT) scans may predict clinical outcomes such as survival in patients with idiopathic pulmonary fibrosis (IPF), according to a study.
The study, “Thoracic skeletal muscle quantification: low muscle mass is related with worse prognosis in idiopathic pulmonary fibrosis patients,” was published in the journal Respiratory Research.
Sarcopenia, or the degenerative loss of skeletal muscle mass, is associated with poor outcomes, including in terms of disability, quality of life, and death, in several lung diseases.
Previous studies have found an association between fat-free mass index (similar to body mass index but taking muscle mass into account) and survival in IPF patients. However, detailed muscle mass quantification to establish sarcopenia had not been analyzed in this clinical context.
Researchers at Yonsei University College of Medicine in Seoul, South Korea, have now investigated the link between clinical outcomes and sarcopenia using cross-sectional images from chest CT scans — images taken from different angles.
They initially looked at 332 patients diagnosed with IPF between January 2010 and December 2015, with available CT scan images, and clinical data (e.g., body mass index, lung function, and smoking history). Researchers then excluded 152 patients who either underwent lung transplants or were lost to follow-up, leaving 180 patients (143 men and 37 women, with a mean age of 69.1 years).
The team established patient muscle mass indexes by normalizing the CT image cross-sectional area (in square centimeters) with height (in square meters), to account for stature differences in the population. They analyzed muscle mass at the fourth vertebral region (T4; including thoracic muscles), and 12th vertebral region (T12; including muscles that straighten and rotate the back).
Because muscle mass differs between men and women, the researchers treated the results separately.
Results showed that patients with greater sarcopenia had worse forced vital capacity (FVC%; measurement of lung function) than non-sarcopenia patients, and a higher gender-age-physiology index score. Both of these parameters are considered predictive of IPF outcomes.
Furthermore, men with sarcopenia showed a significant reduction in the two-year survival rate compared with non-sarcopenia patients — 58.3% versus 80.4%. In women, the changes were not statistically significant, although researchers saw a trend suggesting a lower two-year survival rate in sarcopenia patients compared with non-sarcopenia ones — 66.7% versus 89.3%.
The team suggested that the small female sample size in the study could explain the nonsignificant trends observed between sarcopenia and survival.
Final analyses of the reported clinical features showed a significant independent association between all-cause mortality and lower T4 muscle index. In contrast, T12 index was not a predictive factor.
The team also found that a higher gender-age-physiology index score was associated with all-cause mortality.
According to the researchers, the link between low T4-associated muscle mass index and poor survival could be explained by either sarcopenia-induced impaired breathing or by reduced lung function affecting the thoracic muscle mass.
“It is unclear whether lower muscle mass led to increased disease severity, or whether increased disease severity led to lower muscle mass. Further studies investigating this mechanism are thus required,” they wrote.
Still, they suggested that skeletal muscle mass measured by chest CT could have prognostic value in patients with IPF.
“Low skeletal mass normalized for stature at the level of 4th vertebrae, which can be acquired by quantifying thoracic skeletal muscle on single-slice axial chest CT, may be a strong risk factor for all-cause mortality in patients with IPF,” the researchers concluded.