Mucus plugs have been described in the pathology of asthma and COPD for a long time and treated clinically as scenery. A review of the recent work argues that this has changed, and sets out why: plugs form through mucus hyperconcentration, altered viscoelastic properties, impaired clearance and mucociliary collapse - a chain with several points at which treatment could act.
What moved it from pathology to practice was measurement. Scoring plug burden by bronchopulmonary segment on computed tomography produced a number, and that number has been associated with more exacerbations and faster spirometric decline in both asthma and COPD, and with higher mortality in COPD. Quantitative image-processing methods are in development. Most importantly, plug burden has now been used as an endpoint in trials of biologic therapy in asthma, where several agents reduced it with accompanying improvement in spirometry - which is what distinguishes a treatable trait from a prognostic marker.
The practical point is that these plugs are already visible on scans you are already ordering, and are routinely not reported. A patient with poorly controlled asthma and a heavy plug burden is a different patient from one with none, both in expected trajectory and in likely response to a biologic. Ask for it to be commented on. What is missing before this becomes protocol is standardised imaging and scoring methodology, which the authors identify as the next requirement.
- Ask the radiologist to comment on mucus plugging when a CT is done for uncontrolled asthma or COPD.
- Read a heavy plug burden as a marker of worse trajectory, not as an incidental finding.
- Note that biologic therapy has reduced plug burden with spirometric improvement in asthma trials.
- Do not act on plug scores as a threshold; methodology and imaging protocols are not yet standardised.
- Consider it when deciding whether an uncontrolled asthmatic warrants escalation to a biologic.
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