Following confirmation of a diagnosis of asthma and after comorbidities have been addressed, severe asthma is defined as ‘‘asthma which requires treatment with high dose inhaled corticosteroids (ICS) plus a second controller (and/or systemic corticosteroids) to prevent it from becoming ‘uncontrolled’ or which remains ‘uncontrolled’ despite this therapy.’’ – (Chung et al. 2014)
Having severe asthma symptoms does not necessarily mean that the person has “severe asthma”. To explain this, it is important to understand two key concepts in asthma management: asthma control and asthma severity.
Well-controlled asthma means that asthma symptoms are infrequent (twice a week or less), there is no night waking due to asthma, no limitation of normal activities, and the person is at a low risk of flare-ups.
Uncontrolled asthma, as well as burdening the patient with symptoms, can result in frequent flare-ups / attacks, adverse reactions to medication and chronic morbidity. In Australia, about 45% of adults with asthma have uncontrolled symptoms, and around one quarter have had a flare-up in the past year (Reddel et al. 2015). Some patients have risk factors that increase their chance of flare-ups, even if they have few symptoms (Bateman et al. 2015, Loymans et al. 2016, GINA 2017).
Mild asthma is asthma that can be well-controlled with a low-dose inhaled corticosteroid preventer.
Severe asthma (also called ‘severe refractory asthma’) is asthma that remains uncontrolled (symptoms and/or flare-ups) despite treatable factors having been addressed and maximal inhaled therapy being taken, or, in a few patients, remains well-controlled only while high dose treatment is being taken. ‘Refractory’ means that the person’s asthma does not respond as well to treatment as it does for most people. For more information, see Diagnosis.
For strategic reasons in developing countries, the World Health Organisation (WHO) defines an additional category called “untreated severe asthma”. This refers to people with severe symptoms resulting from undiagnosed asthma, or unavailability of treatments (Bousquet et al. 2010). When inhaled corticosteroids are made available, asthma morbidity is dramatically reduced (Cerci Neto et al. 2008).
Most people with asthma experience mild to moderate symptoms, and most can respond well to standard preventer therapies (inhaled corticosteroids with or without long-acting beta2-agonists (LABAs)). However, some people continue to experience poor symptom control or flare-ups, despite being prescribed maximum doses of preventer medication. This is called ‘difficult-to-treat asthma’. For many of these patients, this is because of problems that can be treated, including not using their preventer inhaler correctly or not taking it regularly, or because they also have other conditions such as sinusitis or obesity (called ‘comorbidities’) that can make asthma symptoms worse. Sometimes, it is because they don’t have asthma, but their respiratory symptoms are due to another condition such as cardiac disease or vocal cord dysfunction.
However, no asthma is the same. Some people with asthma continue to have frequent symptoms, or frequent flare-ups (or both), despite the diagnosis having been checked, other conditions having been treated, and despite them regularly taking maximum doses of inhaled preventer medication. This is called ‘severe asthma’ or ‘severe treatment-refractory asthma’. ‘Refractory’ means that it does not respond as well to normal inhaled preventer treatment as it does for most people.
The ERS/ATS severe asthma guidelines also emphasise that “Inherent in the definition of severe asthma is the exclusion of individuals who present with ‘‘difficult’’ asthma in whom appropriate diagnosis and/or treatment of confounders vastly improves their current condition” (Chung et al. 2014). In population studies, it is therefore not possible at present to identify patients with severe asthma, as severe asthma is a diagnosis of exclusion.
Within the clinic, it can be difficult to differentiate between these patient subsets (particularly difficult-to-treat and treatment-refractory). It is important to recognise that differences exist, as symptoms may result from differing underlying causes, which in turn require different intervention approaches. For more information, see Diagnosis.
Last Updated on
