Chronic respiratory diseases: mucus plugs associated with poorer lung function

High prevalence, but varying across studies

This systematic review and meta-analysis brings together studies on mucus plugs in several chronic respiratory diseases. Two authors searched four databases for eligible studies.

The pooled prevalence is 63% in asthma, with a 95% confidence interval ranging from 52 to 74%. It is 47% in COPD, with an interval of 38 to 55%, and 63% in cystic fibrosis, with an interval of 46 to 81%.

These estimates describe the populations included in the studies. They do not mean that everyone with one of these diseases has the same probability of having mucus plugs. The confidence intervals, particularly in cystic fibrosis, indicate substantial uncertainty.

Associations with respiratory function and complications

In asthma, the presence of plugs is associated with higher eosinophil counts and exhaled nitric oxide levels, as well as poorer lung function measurements. In COPD, it is associated with older age, lower body mass index and reduced respiratory function, among other factors.

In patients with COPD, the authors also report an association with more acute exacerbations, higher mortality, longer hospital stays and higher hospitalization costs. The abstract does not provide the sizes of these associations or the absolute risks, so their clinical significance cannot be quantified.

A research avenue, not a proven treatment strategy

The authors propose studying mucus plugs as a potentially treatable trait. This is a research perspective, not evidence that treatment targeting these plugs would reduce hospitalizations or mortality.

Differences between studies remain important when interpreting the findings. The reported analyses suggest that certain inflammatory, respiratory and treatment-related parameters contribute to this variability. The abstract alone does not allow a full assessment of study quality or how well confounding factors were controlled.

What we can take away

Mucus plugs appear to be a marker of more severe respiratory disease. This review is not enough to establish their causal role or the benefit of treatment targeting them.