We reexamined whether increased CRS could predict the clinical effect of BT in 12 cases. Patients were assessed before receiving treatment (baseline) and at least 2 years after the final BT treatment. Moreover, 6 of the 12 patients responded positively to BT. However, CRS did not predict response to BT. In contrast, patients who responded to BT exhibited desensitization of CRS to capsaicin accompanied by improvement of cough-related QOL after BT.
We previously reported that increased CRS to capsaicin might predict positive BT response [8]]; however, we were unable to confirm similar results in this study. Two patients with increased CRS, who were initially considered BT responders, experienced exaggerated asthma symptoms as well as worsened QOL and symptom control 1 year after their last BT treatments. These differences may be attributed to the short follow-up period (≤ 2 years) in our previous report, and the administration of systemic steroids with BT may have masked the true therapeutic effect of BT. We postulate based on these cases that follow-up periods of < 2 years do not accurately reflect the therapeutic effects of BT. Severe asthma exacerbation, hospital emergency department visits, AQLQ and ACQ more worsened during 1year than that of during 2 years in long-term (> 10 years) prospective, follow-up study [10]]. We need to carefully follow-up the patients received BT over long time because optimal predictors of BT response are still unknown [10, 11].
Our results showed that BT desensitized cough CRS to capsaicin, a phenomenon particularly remarkable in patients who responded to BT. Moreover, decreased CRS was accompanied by improved LCQ scores. To the best of our knowledge, this is the first report to demonstrate BT desensitized CRS in consecutive case series. Several studies have demonstrated that denervation in the airways may contribute to the clinical efficacy of BT [12–14]. In our study, the cough reflex desensitization to capsaicin observed in BT responders is consistent with that of previous reports on airway denervation effects of BT.
Our study has several limitations. First, it was a single-center retrospective study that included only 12 patients. Second, there were few male patients in the study; therefore, differences in efficacy due to sex could not be evaluated. Third, the appropriate period to judge the effects of BT could not be determined. To confirm our findings, larger studies are necessary.
In conclusion, while our results showed that increased CRS to capsaicin does not predict a positive response to BT, we clearly showed that BT desensitizes CRS to capsaicin. Our results may support the denervation effect of BT.