Airway eosinophilia is often found in asthma, and many controller treatments such as inhaled steroids target eosinophilic disease. However, asthma is a heterogeneous disease and a subgroup of patients do not have airway eosinophilia. This study included almost 1,000 patients with asthma and assessed the prevalence and clinical characteristics of the noneosinophilic asthma phenotype.
Sputum eosinophilia (≥2% eosinophils) was found in only 36% of patients with asthma not taking an inhaled corticosteroid (ICS) and 17% of ICS-treated subjects with asthma. Absence of eosinophilia was noted frequently.
Eosinophil. Image source: Wikipedia.
In repeated analyses of people with asthma not taking an ICS, only 22% had sputum eosinophilia on every occasion (persistent eosinophilia), while 47% had no eosinophilia on every occasion (persistently noneosinophilic).
Two weeks of combined antiinflammatory therapy caused improvements in airflow obstruction in eosinophilic asthma, but not in persistently noneosinophilic asthma. In contrast, bronchodilator responses to albuterol were similar in eosinophilic and noneosinophilic asthma.
Approximately half of patients with mild-to-moderate asthma have persistently noneosinophilic disease, a disease phenotype that responds poorly to currently available antiinflammatory therapy such as ICS. Measurements of FeNO are recommended in the current ATS guidelines (Am. J. Respir. Crit. Care Med. Vol 184. pp. 602-615, (2011). However, FeNO may not be helpful in patients with noneosinophilic asthma.
Asthma Inhalers (click to enlarge the image):
A Large Subgroup of Mild-to-Moderate Asthma Is Persistently Noneosinophilic. Am. J. Respir. Crit. Care Med. March 15, 2012 vol. 185 no. 6 612-619.