The airflow limitation in asthma occurs through both airway hyperresponsiveness to external stimuli and chronic airway inflammation. Airway constriction is regulated by nerves to the smooth muscles of the airway. Beta-2 nerve receptors have long been the target of asthma therapy with both short-acting beta-2 agonists (SABAs) as rescue treatment and long-acting beta-2 agonists (LABAs) as maintenance therapy.3,4 However, there is increasing evidence that cholinergic nerves also have a role in airway regulation in asthma, and long-acting muscarinic antagonists (LAMAs) have recently shown benefit as add-on therapy in some types of asthma.4-6 Inhaled corticosteroids (ICSs) have long held an important role in reducing airway inflammation, especially in the setting of allergic or eosinophilic inflammation.3-5
Spirometry is essential to asthma Dx—but what about FeNO?
The mainstay of asthma diagnosis is confirming both a history of variable respiratory symptoms and variable expiratory airflow limitation exhibited by spirometry. Obstruction is defined as a reduced forced expiratory volume in 1 second (FEV1) and as a decreased ratio of FEV1 over forced vital capacity (FVC) based on predicted values. An increase of at least 12% in FEV1 post bronchodilator use indicates asthma for adolescents and adults.
More recently, studies have examined the role of fractional exhaled nitric oxide (FeNO) in the diagnosis of asthma. The 2020 Focused Updates report states that FeNO may be useful when the diagnosis of asthma is uncertain using initial history, physical exam, and spirometry findings, or when spirometry cannot be performed reliably.5 Levels of FeNO > 50 ppb make eosinophilic inflammation and treatment response to an ICS more likely. FeNO levels < 25 ppb make inflammatory asthma less likely and should prompt a search for an alternate diagnosis.5 For patients with FeNO of 25 to 50 ppb, more detailed clinical context is needed. In contrast, the 2022 GINA updates conclude that FeNO is not yet an established diagnostic tool for asthma.4
Management
When to start and adjust an ICS
ICSs continue to be the primary controller treatment for patients with asthma. However, the NAEPP and GINA have provided different guidance on how to initiate step therapy (TABLE3-5). NAEPP focuses on severity classification, while GINA recommends treatment initiation based on presenting symptoms. Since both guidelines recommend early follow-up and adjustment of therapy according to level of control, this difference becomes less apparent in ongoing care.
A more fundamental difference is seen in the recommended therapies for each step (TABLE3-5). Whereas the 2020 Focused Updates prefers a SABA as needed in step 1, GINA favors a low-dose combination of ICS-formoterol as needed. The GINA recommendation is driven by supportive evidence for early initiation of low-dose ICS in any patient with asthma for greater improvement in lung function. This also addresses concerns that overuse of as-needed SABAs may increase the risk for severe exacerbations. Evidence also indicates that the risk for asthma-related death and urgent asthma-related health care increases when a patient takes a SABA as needed as monotherapy compared with ICS therapy, even with good symptom control.7,8
Continue to: Dosing of an ICS