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The topic today is going to be treatment of viral respiratory infection-induced asthma in young children. While this is a specific component of the asthma problem, what I hope to show you, it is perhaps the most important component of asthma that we, as pediatricians, deal with. And although I'm going to focus eventually specifically on this aspect of asthma management, I need to put this into overall perspective in the broad picture of asthma.
There are many issues related to asthma, and many treatments. What I hope to focus on are which are the most important? I'm sure all of you are aware of the NINDB guidelines on asthma management, it's 134 pages with 15 flow diagrams and boxes and arrows going in every which direction, and somewhere through all that, you need to winnow down on which things make a difference and which are really important.
I think we as pediatricians do deal with the beginning of life, with the very youngest ones, and I want to start with where asthma starts in the beginning. [Please play video clip above.] That, of course, is not yet asthma, this is something we all see a great deal of, it's bronchiolitis.
But let's talk about bronchiolitis and how it relates to asthma. They both have in common lower airway obstruction. Both cause lower airway obstruction with inflammation and bronchial smooth muscle spasm, and the same viruses, respiratory syncytial virus to a major extent, parainfluenza to a somewhat lesser extent, are the agents that cause bronchiolitis, but they are also the major triggers for acute exacerbations of asthma in preschool age children. Other common cold viruses, and RSV is nothing but a common cold virus that children and adults get over and over again, also trigger asthma. The rhinoviruses begin to predominate in school age children and adults.
When an Infant Gets RSV
What happens when that otherwise healthy infant gets RSV, what happens to them subsequently? Well, the majority of children who get respiratory syncytial virus infection only get a cold. All they get is rhinorrhea. A smaller number, depending probably on genetic predisposition and perhaps some prenatal factors, get the lower airway obstructive phenomena that we call bronchiolitis. Of those who get bronchiolitis, about half get no recurrent lower respiratory illness with viral respiratory infections, they just get colds after that, but about an equal number get recurrent lower respiratory illness with viral respiratory infections that can be called an intermittent pattern of asthma. Some of those, again depending upon genetic predisposition we call atopy, the predisposition to make specific immunoglobulin-E antibody to inhalant allergens in our environment, go on and get more chronic or persistent asthma.
Just What Is Asthma?
What is asthma? Some people say, I don't know if I can define it, I know it when I see it, like love, but I think you can define it, I think you can define anything if you think about it a bit, and it's been defined in somewhat different ways, but basically they come down to this: it's a physiologic abnormality of the airways characterized by hyperresponsiveness to various stimuli resulting in airway obstruction, reversible either spontaneously or as a result of treatment, and that airway obstruction is the result of various degrees of bronchial smooth muscle spasm and inflammation. We say it sometimes in different ways.
How many of you make the diagnosis of reactive airway disease - RAD? Looks like about half the audience. Anyone know if there is an ICD-9 code for RAD? This was an editorial in one of the pulmonary journals, "Reactive airway disease, a lazy term of uncertain meaning that should be abandoned." This was by Drs. Fahy and O'Byrne from the Cardiovascular Research Institute in California and McMaster University in Hamilton, Canada. This is from the American Journal of Respiratory and Critical Care Medicine, Volume 163, No. 4, March 2001, 822-823. Why don't they like it? Because it's a sloppy term. Someone comes in and requires bronchodilators or something, so they say, Oh, they've got reactive airway disease. But I often say that reactive airway disease is a term used by people with a speech defect; they have a problem saying the word asthma. What is airway hyperreactivity? Airway hyperreactivity specifically means responsiveness to substances such as histamine or methacholine. It's not a diagnostic test for asthma, all asthmatics, at least when they're actively having asthma, do have airway hyperreactivity, but so does 10% of the normal population, 30% of people who just have allergic rhinitis, so it's not a specific phenomenon for asthma.
There is an entity described in the medical literature with a little bit of controversy related to it that's called reactive airway dysfunction syndrome, it's not something we see commonly in pediatrics, I think I've seen one case. These are asthma-like symptoms following single exposure to high levels of a potent irritant, it's predominantly an occupational phenomenon, and occupational medicine specialists are quite familiar with this disorder. These are people who had no prior history of asthma, don't seem to have a genetic predisposition, so far as anyone can tell, although they may, and they get exposure to essentially a toxic substance, and then have for a period of time, going on for many months generally, asthma-like symptoms. And because of the confusion with the terms airway hyperreactivity, which has a specific meaning, and the reactive airway dysfunction syndrome, which is a specific syndrome, the term reactive airway disease really should not be used. Take a better history, determine if they have some other underlying problem, or if, in fact, it is asthma.
Now, what are some of the various stimuli that are involved in the airway obstruction of asthma? We'll get into this definition of asthma, that is hyperresponsiveness to various stimuli. I'm putting viral respiratory infections at the top, because, as I show you, they contribute to some of the most important degrees of morbidity, and these are strictly the common cold viruses. RSV in infants, toddlers, preschools; rhinoviruses in school-age children and adults. Allergens become very important and progressively important as children with asthma get older, and continue to have symptoms, these can be outdoor, they can indoor, there are lung irritants; cigarette smoke has been shown in many studies to be a major factor to which airways of asthmatics are hyperresponsive, and these children have greater frequency of respiratory symptoms by a variety of measures. Leaf and trash burning is a primitive custom that still goes on in many parts of this country. I've seen patients end up in intensive care units because of intense exposure to leaf and trash burning immediately up-wind from them; strong odors cause problems; physical factors, such as exercise, cold air, all are factors to which the airways are hyperresponsive.