Muco-Obstructive Lung Disease: A Systematic Review

Abstract

Muco-obstructive lung disease is a new classification under the diseases of respiratory tract. A lot of discussion is still going on regarding this new group of diseases. It is characterised by obstruction of the respiratory tract with a thick mucin layer. Usually in normal individuals, the mucus is swept out of the respiratory system while coughing in the form of sputum or phlegm, but if the consistency of the mucus is thick, or the amount is heavy or there is a certain defect in the ciliary function of the respiratory tract, the mucus is not cleared and it gets accumulated in the lungs alveoli, therefore blocking it. The mucus trapped in the distal airways cannot be cleared by coughing therefore forming a layer in the alveoli and bronchioles. Long-standing condition causes inflammation and infection. This new group of diseases specifically includes chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF), primary ciliary dyskinesia (PCD) and non-cystic fibrosis bronchiectasis (NCFB). Asthma, although an obstructive disease of the lung, is not particularly included under muco-obstructive lung disease. The major symptoms with which these diseases present are sputum production, chronic cough and acute exacerbations of the condition. The mucus adheres to the lung parenchyma causing airway obstruction and hyperinflation. In this article, we will see how muco-obstructive lung diseases affect the normal physiology of the respiratory system and how is it different from other obstructive and restrictive lung diseases. We will individually look into all the four conditions that come under the category of muco-obstructive lung diseases.

Keywords: copd; cystic fibrosis; infection; muco ciliary clearance; mucus; non-cystic fibrosis bronchiectasis; obstructive lung disease; primary ciliary dyskinesia; respiratory tract.

Figure 1. PRISMA flow diagram of muco-obstructive lung diseases

Adopted from the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA).

Figure 2. Diseases under muco-obstructive lung disease

COPD: Chronic obstructive pulmonary disease; NCFB: Non-cystic fibrosis bronchiectasis Image credits: Garima Singh