A wide range of causes of bronchiectasis has been reported in adults, however, in half the cases no specific cause is confirmed. When an underlying medical condition causes the bronchiectasis, this underlying condition is called a “co-morbidity.”
Approximately one third of cases are diagnosed after a lung infection that damages the airways for the first time. Such infections include bacterial pneumonia, whooping cough (pertussis), NTM (nontuberculous mycobacteria) or tuberculous among others. Bronchiectasis can also occur with minimal or silent infections in which the infection does not manifest as an illness as no symptoms are recognized during the course of the infection.
Repeated infections and the inflammation associated with those infections can worsen bronchiectasis. These events can also damage the cilia, which are one of the lungs’ natural defense and airway clearance mechanisms. Cilia are small, hair-like structures that line the airways and beat rapidly in sequence help expel mucus.
The initial lung damage that leads to bronchiectasis can begin in childhood. However, symptoms may not appear until months or years later, often after repeated lung infections. This chronic inflammatory airway disease can affect one section of a lung or multiple sections of both lungs.
Bronchiectasis can be congenital (present from birth) or acquired. Congenital bronchiectasis affects infants and children as a result from genetic abnormalities that affect the normal function of the airways. Acquired bronchiectasis is more common and occurs as a secondary effect of another factor such as infection. Acquired bronchiectasis can affect adults and older children. Bronchiectasis usually results as a response to some other condition rather than as a condition that initiates on its own.
In the United States, common childhood infections that cause damage to the airways—such as whooping cough and measles—used to cause many cases of bronchiectasis. These infections are now less common because of widespread use of vaccines. In all populations, tuberculosis, NTM (nontuberculous mycobacteria), fungal infections, and pneumonia can also cause bronchiectasis. There is growing evidence that NTM is a key infection associated with bronchiectasis in North America, but it is not always known which occurs first, bronchiectasis or NTM.
Although smoking does not cause bronchiectasis, it can make a patient’s condition and symptoms worse and lead to more rapid lung function decline.
While vaccines and antibiotics helped to reduce infections and associated damage, other medical conditions that injure the airway walls or prevent the airways from clearing mucus are associated with bronchiectasis. These conditions may be genetic in origin, or result from exposures, medical conditions, or events that occur “outside” our genes. For example, bronchiectasis that affects only one part of the lung may be due to a blockage.
Medical conditions that damage the airways and raise the risk of bronchiectasis and lung infections include the following:
Unknown or idiopathic causes, meaning no identified cause
Bronchiectasis can affect anyone regardless of age. Because the condition is not reversible, the percentage of people affected by the condition increases with age. However, children with CF and other diseases such as NTM, Alpha-1, COPD, and asthma have higher rates of bronchiectasis than other children.