Monday, February 11, 2013

Can Asthma Turn into Emphysema?

For the most part, asthma and emphysema are two distinct and unrelated diseases. Asthma most often begins in childhood and is closely related to allergies. Emphysema begins in middle age or later and is almost always due to cigarette smoking. Asthma is a disorder of the bronchial tubes, with difficult breathing resulting from swelling of the air tubes and contraction or “spasm” of the muscles that surround those tubes (“bronchospasm”). Emphysema involves destruction of the walls of the air sacs deep in the lungs (the “alveoli”), and as a result, loss of elasticity of the lungs. In emphysema air easily enters the lungs when we breathe in, but slowly empties from the lungs when we breathe out because the springiness or elasticity of the lungs has been lost, like an old rubber band that has lost its recoil.

And the biggest difference between asthma and emphysema is that persons with asthma who are free of symptoms are expected to have normal or near-normal lung function (their bronchial tube inflammation has abated and their bronchial muscles are not in spasm). Persons with emphysema have permanent loss of lung function; even on a good day, the lung damage remains and breathing capacity is impaired.

But … and there always seems to be a “but” when making general assertions about biology … not everyone with asthma, when well, achieves normal or near-normal lung function. Perhaps you are one of those people with asthma who never smoked cigarettes, have no reason to have emphysema, and yet even under the best of circumstances and with maximal asthma treatment still have reduced lung function. You get short of breath more easily than other people when you exert yourself, and tests of your lung function remain far from normal, even when you are doing well. You have a component of permanent, irreversible narrowing of your bronchial tubes. Doctors sometimes call it “fixed” airways narrowing, in the sense of “stuck” or “immovable.” Although you do not have emphysema (destruction of the walls of the air sacs in your lungs), you have a similar problem: a permanent reduction in your breathing capacity.

It is not difficult to envision that some people with asthma might develop scarring in and around their bronchial tubes, and scar formation lasts forever. All the rest seems to be unknown, however: why do some people with asthma develop this permanent airway narrowing and most others not; when does it happen in the lifelong course of asthma; is it always progressive; and is there any way to prevent it? We know that in persons with asthma, permanent airway narrowing is associated with cigarette smoking; and we shouldn’t smoke. What else? Childhood illness resulting in impaired lung growth? Long-term asthma that has been inadequately treated? Recurrent asthmatic exacerbations that cause a “step-wise” decline in lung capacity?  These are all potential explanations, but none is certain; and different people may be affected by different mechanisms.

No, asthma does not turn into emphysema. But, yes, in some persons asthma can result in permanent narrowing of the breathing tubes that might, strictly speaking, be considered a “chronic obstructive pulmonary disease” or COPD. A “holy grail” of asthma research is discovery of the causes of this scarring of the bronchial tubes and its prevention. We are at the very beginning of a long road to discovery and cure.