So bronchiectis is a very heterogeneous condition, there's more than 100 other underlying conditions that can cause bronchiectis. In around 40% of cases we never find a cause. Uh, the second most common cause is a severe infection, but there's a whole range of conditions going from inherited disorders like cystic fibrosis and primary ciliary dyskinesia. Uh, atypical infections like non-tuberculous mycobacteria, rheumatological conditions, rheumatoid arthritis, other connective tissue diseases, inflammatory bowel disease, um, uh, there are so many causes, uh, we could spend the rest of this, uh, this module going through all of those underlying diseases. As a result of the different causes, patients can present in very different ways, but some patients present with symptoms during childhood, some patients, the disease starts very late in life. There's also a huge international geographical heterogeneity in the disease that's important to consider. Globally, tuberculosis may be the leading cause of bronchiectis in places like India where we've done quite a lot of bronchiexis research, by far the most common cause is post-tuberculous lung disease, you get bronchiectis as a result of both traction from lung destruction and endobronchial uh TB. Uh, and so you see very different patients in those countries with a high TB burden than you do in, uh, in the, the setting where I work, which is a low TB incidence area. Um, and so we see big, big differences in the cause and consequences of bronchiectis between different regions, uh, different characteristics again in China, lots of post-infective disease. In the United States, we see a lot of non-tuberculous mycobacterial infections, also in South Korea, but in Scotland where I work or in Southern Europe, there seems to be less of those pathogens. Uh, and so you do see this, this important, uh, difference in the disease, depending on where you work and depending on the characteristics of the patients in front of you. Um, nevertheless, the fundamentals of the disease are the same, all of these conditions that I'm talking about are a result of impaired mucociliary clearance, inflammation, and infection. Infection's another area where we see important heterogeneity, so patients can be infected over time with a variety of pathogens, uh, the lungs fail to clear bacteria effectively because of impaired mucociliary clearance, uh, and that leads to chronic infection with bacteria. The most common bacteria globally is Pseudomonas, uh, and that's consistent across different regions. Uh, the second most common is Haemophilus, but that shows very strong geographical variation, a lot in Northern Europe, much less in Southern Europe and Asia, for example. Um, chronic infection is associated with worse outcome, more exacerbations, it's a sign of, uh, that the biology of the disease is highly active, and so it's an important thing to recognize. Thinking about the, the recognition of the disease, there's a, there's an important implication of what I've just talked about in terms of bronchiectis being associated with all of these other conditions. If COPD can be a cause, if asthma can be a cause, if rheumatoid arthritis can be a cause, inflammatory bowel disease, um, people with bronchiectis will be presenting to lots of different specialists, not just pulmonologists, but actually rheumatologists, uh, infectious. Diseases doctors, uh, and so all need to be aware of the potential for bronchiectis in these subsets of patients. Some estimates are 10% of rheumatoid patients will end up with bronchiectis. So rheumatologists need to be aware of this, uh, of this potential. So I think it's really important that if you've got a patient with a chronic cough, uh, particularly if that's associated with sputum production, or if somebody's having recurrent infections, recurrent pneumonias. Uh, things that sound like exacerbations, if they have any of these associated conditions in particular, should have a high index of suspicion for bronchiectis, and we should be looking to, to get people to a CT scan as early as possible.
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