Blood eosinophils as a predictor of treatment response in adults with difficult-to-treat chronic cough

Abstract

There is lack of evidence on the role of blood eosinophil count (BEC) as a predictor of treatment response in patients with chronic cough. The study aimed to evaluate BEC as a predictor of treatment response in all non-smoking adults with chronic cough and normal chest radiograph referred to cough clinic and in a subgroup of patients with chronic cough due to asthma or non-asthmatic eosinophilic bronchitis (NAEB). This prospective cohort study included 142 consecutive, non-smoking patients referred to our cough centre due to chronic cough. The management of chronic cough was performed according to the current recommendations. At least a 30-mm decrease of 100-mm visual analogue scale in cough severity and a 1.3 points improvement in Leicester Cough Questionnaire were classified as a good therapeutic response. There was a predominance of females (72.5%), median age 57.5 years with long-lasting, severe cough (median cough duration 60 months, severity 55/100 mm). Asthma and NAEB were diagnosed in 47.2% and 4.9% of patients, respectively. After 12-16 weeks of therapy, a good response to chronic cough treatment was found in 31.0% of all patients. A weak positive correlation was demonstrated between reduction in cough severity and BEC (r=0.28, p<0.001). Area under the curve for all patients with chronic cough was 0.62 with the optimal BEC cut-off for prediction of treatment response set at 237 cells·µL^-1 and for patients with chronic cough due to asthma/NAEB was 0.68 (95% CI 0.55-0.81) with the cut-off at 150 cells·µL^-1. BEC is a poor predictor of treatment response in adults with chronic cough treated in the cough centre.

FIGURE 1

Study design. VAS: visual analogue scale; LCQ: Leicester Cough Questionnaire; CT: computed tomography; BEC: blood eosinophil count; sIgE: specific immunoglobulin E; F_ENO: exhaled nitric oxide fraction; MCT: methacholine challenge test; NAEB: non-asthmatic eosinophilic bronchitis; UACS: upper airway cough syndrome; GER: gastro-oesophageal reflux; RCC: refractory chronic cough; UCC: unexplained chronic cough; ICS: inhaled corticosteroids; LABA: long-acting β₂-agonist; LTRA: leukotriene receptor antagonist; OCS: oral corticosteroid; OAH: oral antihistamines; INAH: intranasal antihistamines; INCS: intranasal corticosteroids; PPI: proton pump inhibitor.

FIGURE 2

Flowchart of included groups.

FIGURE 3

Prevalence of eosinophilia in subgroups with different causes of chronic cough. BEC: blood eosinophil count; NAEB: non-asthmatic eosinophilic bronchitis; UACS: upper airway cough syndrome; GER: gastro-oesophageal reflux; BHR⁺: presence of bronchial hyperresponsiveness; RCC: refractory chronic cough; UCC: unexplained chronic cough.

FIGURE 4

a) Correlation between reduction in cough severity and blood eosinophil count in all patients with chronic cough. b) The receiver operating characteristic curve with analysis of blood eosinophil count cut-off for prediction of a treatment response in all patients with chronic cough. c) Correlation between reduction in cough severity and blood eosinophil count in patients with asthma or NAEB. d) The receiver operating characteristic curve with analysis of blood eosinophil count cut-off for prediction of a treatment response in patients with asthma or NAEB. NAEB: non-asthmatic eosinophilic bronchitis; VAS: visual analogue scale.