What is Severe Asthma?

What is Severe Asthma?

At my last appointment with Dr. Smartypants, I asked her what my asthma phenotype is. Every so often I become more curious about just how she came to the “severe” part of the "moderate-to-severe [well-controlled] asthma with a mild atopic component” conclusion. (As my friend Stephen said, “Sounds like she wanted to make sure her bases were covered”!)

To “decode” or demystify my own asthma, tonight I read all 77 relevant pages of the 112 page International ERS/ATS Guidelines on Definition, Evaluation and Treatment of Severe Asthma document. (Just a little light bedtime reading at 11:30 PM. Like you do.) In the event you want to reference the work, because this document is ridiculously long, I’ve included page numbers alongside my citations. In this post, I’ll approach defining severe asthma. In part 2, I’ll apply what I’ve learned to my own asthma, per my experiences and as described by my asthma specialist.

How is severe asthma defined?

Per the European Respiratory Society/American Thoracic Society article, asthma is classified as severe when it “requires treatment with high dose inhaled corticosteroids [ICS]”, as well as another controller medication, “and/or systemic corticosteroids” (ie. prednisone), to prevent a decline in asthma control, as well as asthma that remains uncontrolled despite maximal therapy.1[3] Severe asthma is often seen as a distinct form of asthma, with multiple phenotypes (presentations) under the “severe asthma” umbrella.1[12]

Uncontrolled or difficult-to-treat asthma is not by default severe asthma. Per this definition, it includes only those with “refractory”—stubborn or treatment resistant—asthma, and those in progress of addressing co-morbidities that may worsen asthma (ie. obesity, acid reflux, sinus disease), but who do have confirmed asthma.1[17, 3] Those with severe asthma are on significant or maximal intervention for asthma, per the Global Initiative on Asthma (GINA) guidelines—requiring high dose ICS and long-acting bronchodilator, orleukotriene receptor antagonist (ie. Singulair) or theophylline for the previous year or having required oral steroids for half the year or more.1[68]

How is severe asthma different from mild or moderate asthma?

The core difference between mild or moderate asthma and severe asthma is the amount of corticosteroid, inhaled or systemic, required to manage it, plus need for additional controller medications as above.1[17] A component of severe may include insensitivity to corticosteroid as a contributing factor—either resulting in poor control despite high dose ICS or oral steroids, or worsening of control when oral/ICS is decreased.1[37]

Controlled or uncontrolled?

The response to therapeutic intervention (AKA medication) is what determines whether or not someone has “controlled” or “uncontrolled” severe asthma.1[17]

I fall into the “controlled” category—thankfully. The Guidelines summarize my experience here well, in that I am well maintained on high dose ICS, however, when ICS is decreased, a loss of control—worsening of symptoms—occurs.1[68] Thus, people with “controlled” severe asthma require remaining in the “high dose” inhaled steroid threshold to maintain control.1[68]

Uncontrolled severe asthma consists of at least one of the following: poor symptom control, frequent severe exacerbations requiring exacerbations (requiring oral steroids more than once in a year), requiring a hospitalization/ICU stay/intubation, or airflow limitation, in addition to being on what I described as significant or maximal intervention above.1[68] I would think, as well, that “uncontrolled severe asthma”, is more what people think about when they think “severe asthma”—I know I did!

Is severe asthma a whole other type of asthma? A completely different disease?

Some researchers think it might be, as it has distinct phenotypes or clusters, and generally “behaves” differently than mild-to-moderate asthma. However, benefit may not be gleaned by separating severe asthma from mild-to-moderate, as the general treatment methods are the same and mechanisms are similar. Severe asthma affects somewhere between 5 to 10% of people with asthma1[20], and when it comes to research funding, sometimes you’re better off being the small fish in the big pond! The reality is, severe asthma, especially when it is uncontrolled, uncontrollable, and accompanied by significantly decreased lung function and severe or life-threatening exacerbations, can impact every aspect of a person’s life. This makes certain types of severe asthma a very different experience than those with mild-to-moderate have, and even from those with severe-but-controlled asthma.

In “What is Severe Asthma? Part 2: Decoding my phenotype”, I’ll write more about my own asthma, and how Dr. Smartypants may have come to the conclusion to describe my asthma as “moderate-to-severe”… but well controlled.

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