Severe asthma has its own distinct pathophysiology, here’s why certain treatments are so important

Severe asthma represents a unique clinical entity with its own pathophysiology that is distinct from mild to moderate disease, and therefore requires tailored therapy to achieve optimal control and prevent long term complications, says Associate Professor John Brannan, Scientific Director at Department of Respiratory and Sleep Medicine at John Hunter Hospital in NSW.

A key differentiator in severe asthma is that airway obstruction may become irreversible, Associate Professor Brannan says.

“If you have chronic, severe asthma and inflammation in your airways that has been going on for some time, the inflammation changes the underlying pathological structure within the airways and the airway obstruction becomes fixed.”

This is one reason why it is critical to use spirometry to identify and characterise severe disease.

Another reason is that not all patients with severe disease will report severe symptoms.

“It is the nature of airway disease, after a while the patient becomes so used to their symptoms, that as far as they’re concerned, it’s nothing they need to bother a doctor about,” says Associate Professor Brannan.

GPs and patients face barriers in accessing good quality spirometry, but Associate Professor Brannan says “it’s worth going to the effort if you can.” GPs can upskill in this area by undertaking spirometry education courses.

If fixed airway obstruction is identified in a patient with asthma, it represents a disease subtype where triple therapy may be indicated.

This involves adding an anticholinergic to the standard regime of an inhaled corticosteroid and long-acting beta agonist.

The rationale for adding an anticholinergic (or a long acting muscarinic) such as tiotropium to treat severe asthma lies in the pathophysiology.

“It appears to be in severe disease where it makes a difference, because of the remodelling in the airway,” Associate Professor Brannan says. “So in mild disease, where you’re walking around with normal or close to normal lung function, cholinergic drive is not having really much of an influence on airway calibre.”

“However, cholinergic drive to the airway may have more of an influence when your airways become more narrow or that ‘fixed’ component is established”. He continued, “Even small improvements in airway calibre, with the addition of the anti-cholinergic, can have a larger improvement on airway resistance, improving symptoms.”

“So if you have significant airways disease with obstruction and cholinergic drive is having some influence, if you can reduce cholinergic drive and even cause some degree of airway stabilisation or even a small degree of bronchodilatation, you’re going to have an improvement on the symptoms of these patients.”

By utilising spirometry, GPs can assist in prescribing triple therapy and can continue to play an important role in asthma management. However, all patients suspected to have severe asthma should be referred to a respiratory physician for review. In addition, some patients may also require biological therapy and this can only be prescribed by respiratory physicians for severe asthma.

In terms of disease trajectory for severe asthma, Associate Professor Brannan says evidence is still developing, but research done in patients with COPD, where there is also underlying fixed airway obstruction, suggests treatment with triple therapy can improve and sustain airway calibre so the patient can have stable daily lung function. Further, the addition of inhaled corticosteroid in triple therapy can also reduce mortality and the frequency of exacerbations.

Associate Professor John Brannan will be speaking on this topic at Healthed’s free webcast on Tuesday 28th November. Register here if you’d like to hear more.