Prevalence of severe eosinophilic asthma estimated in Japan
medwireNews: Approximately one third of patients with severe asthma in Japan have severe eosinophilic asthma, show findings from a cohort analysis.
This prevalence was estimated from the health records or insurance claims of 217 patients with severe asthma treated at Kyoto University Hospital between 2009 and 2015. Of these, 160 (74%) had eosinophil assessments that showed 97 (61%) patients had a blood eosinophil count of at least 150 cells/µL, while 54 (34%) had a count of at least 300 cells/µL, and 33 (21%) had a count of at least 500 cells/µL.
The proportion with severe eosinophilic asthma, defined as an eosinophil count of 300 cells/µL or above, was therefore 34%.
There was no significant difference between patients with eosinophilic and non-eosinophilic asthma in the risk for exacerbations, with a similar proportion of patients in each group experiencing at least one, at 31% and 27%, respectively. The annual mean number of exacerbations requiring an emergency room visit was also comparable, at a corresponding 0.06 and 0.07.
However, the two groups did differ in terms of immunoglobulin E and exhaled nitric oxide (FeNO) levels, which were both increased in patients with eosinophilic versus non-eosinophilic asthma, while the ratio of forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC) was reduced.
Indeed, on multivariate analysis (Lasso negative binomial regression model), patients with eosinophilic asthma who had a percent predicted FEV1 below 60% had 3.3 times the rate of future exacerbations compared with patients with higher levels, while those with a FeNO level of at least 25 ppb had 302 times the rate compared with patients with lower levels (p=0.03; confidence interval [CI]=1.16 to 9.57 and p<0.0001; CI=84 to 1086, respectively).
These characteristics did not predict future exacerbation rate among patients with non-eosinophilic asthma, however. For this group, the main rate-determining factor was having an exacerbation during the baseline period, which increased the rate by 6.9 times compared with not experiencing an exacerbation (p=<0.0001; CI=2.97 to 16.2).
“[T]he differences in exacerbation risk factors seen between eosinophilic and non-eosinophilic subgroups highlight the significance of using blood eosinophil count to stratify subgroups, and that these subgroups may require different management strategies,” note Hisako Matsumoto (Kyoto University) and co-researchers.
They also report that asthma-related costs were similar in the eosinophilic and non-eosinophilic patient groups (¥ 346,554 [US$ 3014; € 2779] and ¥ 479,338 [$ 4168; € 3843] per patient–year, respectively), and that medications accounted for most of the costs in both groups.
“Despite long-term ICS [inhaled corticosteroid] plus non-ICS controller medication, both [severe eosinophilic asthma] and severe non-eosinophilic asthma exert a substantial clinical and economic burden,” the researchers comment.
They conclude in the Journal of Asthma: “There is clearly an unmet medical need for effective treatments for both [severe eosinophilic asthma] and severe non-eosinophilic asthma.”
By Lucy Piper, Senior medwireNews Reporter
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