Asthma- An Allergic Condition

There are a variety of clinical conditions that involve allergy. Asthma is certainly one of the most common. Let us look at asthma through the eyes of an allergist.

First we need to define asthma. The consensus from the experts involved in the most recent NHBBI/NAEPP Guidelines for the Diagnosis and Management of Asthma, 2007 (these are referred to as the National Asthma Guidelines) asthma is defined as a condition that has the following features:

1. Chronic inflammation

2. Involvement of many inflammatory cells

3. Airway hyper-responsiveness and obstruction

4. Possible permanent changes due to inflammation

5. Genetic – Environmental interactions

6. Atopy/Allergy

7. Viral infection and its role in asthma exacerbations and asthma development

Here are a few ‘Factoids’ to know about asthma:

1. Heterogeneity

2. Variability in the clinical course

3. Features cough, wheezing, shortness of breath, reversible airflow obstruction, and hyper-activity (twitchy) airways

4. Can begin early in life with intermittent episodes triggered by viruses

5. Becomes more persistent in those with allergy

6. Can be life long

7. Can see loss of lung function with time

What is wheezing?

This is a hallmark feature of asthma and needs to be defined. Wheezing can come from a variety of clinical conditions; remember that not all that wheezes is asthma.

I always like to be sure that what a family calls wheezing is what I would consider wheezing. We need to be on a common ground in understanding what is going on.

For me a wheeze is a high-pitched whistling sound that tends to be continuous and not broken-up like a crackle/gurgle. Usually this starts with breathing out. With worsening, the wheeze is present breathing out and with breathing in.

Wheezing is common in children

In a population of 6 year old children, 49% had one or more episodes of wheezing. Note, not all go on to have asthma. Asthma is that tendency to have repeated episodes. As with baseball, three strikes and you are out- three separate and distinct episodes are required for the diagnosis.

So what has happened to all those wheezy children?

An excellent epidemiologic study on wheezing in children established three groups of wheezy children. They described early transient wheezers, early persistent wheezers, and late persistent wheezers.

A transient wheezer lost the tendency over time however, the persistent wheezy child continues for a very long period of time to have trouble. The presence of IgE that molecule responsible for allergy was found to be elevated in the persistent groups. So the finding of a marker for allergy had the ability to predict what the future looks like.

The Asthma Predictive Index (API)

This is the best criteria for establishing the diagnosis. The most stringent criteria include the following:

1. Frequent wheezing in the first three years of life

2. One of the following major criteria:

a. Parental history of asthma

b. Physician diagnosed eczema

3. Two of three minor criteria:

a. eosinophilia

b. wheezing without colds

c. allergic rhinitis

The API has at least three features of allergy; eczema, eosinophilia (an inflammatory cell involved in allergic reactions), and allergic rhinitis.

As our understanding of the condition evolves, the involvement of allergy in asthma becomes more substantiated. Allergic sensitization predicts persistence.

Allergic sensitization and allergen exposure early in life

Published work from the Multicenter Allergy Study (Illi S. von Mutius E. Lau S. Niggeman B. Gruber C. Wahn U. Multicentre Allergy Study (MAS) group. Perennial allergen sensitization early in life and chronic asthma in children: a birth cohort study. Lancet 368 (9537):763-70, 2006) looked at this question in more detail. In one of the better ways to study populations, a cohort study involved 499 children with risk factors for allergy and 815 children who had no risk factors (control group). The groups were followed for 13 years. The study found the following:

1. 90% of those with wheezing and no allergy, lost their symptoms by the time they entered school and had normal lung function

2. Sensitization (positive allergy tests) to dust mites, cat, and dog in the first three years of life was associated with continued symptoms and loss of lung function at school age.

3. Airway hyper-reactivity was seen in the sensitized children

4. Sensitization later in childhood had a weak effect and in this study, seasonal allergy did not play a part.

So what were the take home messages from this study?

1. Without allergy asthma goes away

2. Perennial allergens are more important than seasonal allergens

3. The critical time is the first three years of life

4. Food allergy did not lead to a loss of lung function

There are some limitations in extending this study to other populations. This Multicenter Allergy Study was conducted in Europe. Often the populations in European studies are more homogeneous. We tend to be a true melting pot of many types of people, so the nature of the population looked at may limit extending the findings here. Also, I have noted that in European studies on allergy that individuals tend to be mono-sensitive or sensitive to just a few things. In my practice, we see children who are sensitive to many things. So the declaration of allergy tends to be different here versus in Europe. Such a study really needs to be performed here to see if the results are the same in our population of children.

Predictions for adult life

Knowing if allergy is involved with asthma may have some use in predicting what may happen to our children when they become adults.

A study by Porsbjerg, 2006 (Porsbjerg C. von Linstow ML. Ulrik CS. Nepper-Christensen S. Backer V. Risk factors for onset of asthma: a 12 year prospective study. Chest 129:309-16, 2006) looked at the incidence and remission of asthma from childhood to adulthood. If the adult had wheezing as a child, the odd ratio was 3.61 to develop adult asthma. If the adult had diagnosed airway reactivity during childhood, the odds ration was 4.94. The presence of inflamed skin, a dermatitis as a child, had an odds ration of 2.94. Finally, the presence of house dust mite allergy diagnosed in childhood had an odds ratio of 3.23.

A note on odds ratios

This is used when you want to compare the odds of something occurring to two different groups. It is the ratio of the odds for the first group and the odds for the second group (The preceeding information on odds ratios came from the following website ).

So the children who went on to have persistence of their asthma into adulthood were compared to those children who did not have asthma as adults. If the child had sensitivity to house dust mite the odds were 3.23 higher for that child to have continued issues with asthma as an adult.

Clearly, the presence of allergic sensitization in children who wheeze and who have been diagnosed as having asthma can be a marker for the persistence of the condition into the adult years. They really did not outgrow asthma.

Allergy is so interwoven with many aspects of asthma including prediction and prognostication. We need to alway consider asthma as a manifestation of allergy.