Phenotypic characterization of severe asthma.
OBJECTIVE
To highlight recent literature that informs our understanding of severe asthma. Severe asthma is an increasingly important part of specialty practice, is responsible for disproportionate healthcare utilization, and contributes significantly to the costs of care. Better recognition of this subset of asthma can lead to improved healthcare.


RESULTS
Key recent observations in severe asthma include demographic characterizations of several large study populations and the increasing understanding that relative steroid resistance is a virtually universal feature. In addition, strong associations with interleukin-13 and mammalian chitinase have emerged, and abnormalities of endogenous anti-inflammatory pathways have been examined. The role of protein biomarkers to identify and delineate severe asthma is now being investigated. The pathogenic significance of each of these observations is still being clarified, but it appears that severe asthma may have mechanistic underpinnings distinct from that of mild or moderate asthma.


CONCLUSIONS
Severe asthma is a discrete, but variably defined phenotype of asthma. Steroid resistance is extremely common, patients may require doses of inhaled steroids for control that exceed usual guidelines and may also require multiple controller agents. New mechanistic insights could provide important avenues for novel therapeutic interventions.
Ogawa
Yoshiko
Y
Department of Medicine, Baylor College of Medicine, Houston, TX, USA.
Calhoun
William J
WJ
D001249:Asthma / Q000175:diagnosis* / Q000378:metabolism; D015415:Biomarkers / Q000378:metabolism; D002688:Chitinases / Q000378:metabolism; D006801:Humans; D018793:Interleukin-13 / Q000378:metabolism; D010641:Phenotype; D012720:Severity of Illness Index
D015415:Biomarkers; D018793:Interleukin-13; D002688:Chitinases