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Correspondence to: Christopher E. Brightling, MBBS, PhD, Institute for Lung Health, University Hospitals of Leicester NHS Trust Glenfield Hospital, Groby Rd, Leicester LE3 9QP, UK; e-mail: ceb17{at}le.ac.uk
| Abstract |
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Methods: The current literature was reviewed using an Ovid MEDLINE and PubMed literature review for all studies published in the English language from 1963 to December 2004 using the medical subject heading term "eosinophilic bronchitis."
Results: Nonasthmatic eosinophilic bronchitis is a common cause of chronic cough. It is characterized by the presence of eosinophilic airway inflammation, similar to that seen in asthma. However, in contrast to asthma, nonasthmatic eosinophilic bronchitis is not associated with variable airflow limitation or airway hyperresponsiveness. The differences in functional association are related to differences in the localization of mast cells within the airway wall, with airway smooth muscle infiltration occurring in patients with asthma, and epithelial infiltration in patients with nonasthmatic eosinophilic bronchitis. Diagnosis is made by the confirmation of eosinophilic airway inflammation usually with induced sputum analysis after the exclusion of other causes for chronic cough on clinical, radiologic, and lung function assessment. The cough usually responds well to treatment with inhaled corticosteroids. The dose and duration of treatment differ between patients. The condition can be transient, episodic, or persistent unless treated, and occasionally patients may require long-term prednisone treatment.
Conclusions: Further study of this condition may improve our understanding of airway inflammation and airway responsiveness, leading to novel targets for therapeutic agents for the treatment of both asthma and nonasthmatic eosinophilic bronchitis.
Key Words: airway smooth muscle asthma cough eosinophilic bronchitis eosinophils mast cells
| Introduction |
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Studies234 in which the assessment of airway inflammation has been undertaken in chronic cough patients have shown that nonasthmatic eosinophilic bronchitis accounts for 10 to 30% of cases referred for specialist investigation. However, earlier studies56 did not identify patients with nonasthmatic eosinophilic bronchitis as a distinct subgroup among patients with chronic cough. Although we cannot discount the possibility that nonasthmatic eosinophilic bronchitis is a new condition, we feel that the failure to recognize it is more likely to reflect differences in referral pattern. For example many patients, particularly tertiary referrals, are likely to have received a trial of corticosteroids before referral, and asthma may have been diagnosed in those patients who responded to treatment with corticosteroids as having asthma before further tests were done or irrespective of the results of objective tests of variable airflow obstruction or airway responsiveness.
This section addresses the clinical features and management of nonasthmatic eosinophilic bronchitis as a cause of chronic cough. It also highlights advances in our understanding of the pathogenesis of this disorder, which have particularly improved our understanding of the relationship between eosinophilic airway inflammation and disordered airway function in asthma patients. This section was written following a review of all the studies published in the English language from 1963 to December 2004 using an Ovid MEDLINE and PubMed literature review using the medical subject heading term "eosinophilic bronchitis."
| Clinical Features and Diagnosis |
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Nonasthmatic eosinophilic bronchitis is defined as a chronic cough in patients with no symptoms or objective evidence of variable airflow obstruction, normal airway hyperresponsiveness (ie, a provocative concentration of methacholine producing a 20% decrease in FEV1 of > 16 mg/mL), and sputum eosinophilia.2 We used a > 3% non-squamous cell sputum eosinophil count as being indicative of eosinophilic bronchitis as this is outside the 90th percentile for healthy patients (1.1%),8 and this level of sputum eosinophilia has been associated with a corticosteroid response in COPD patients9 and asthma patients.10 The etiology of nonasthmatic eosinophilic bronchitis can be uncertain, although like asthma, nonasthmatic eosinophilic bronchitis can be associated with exposure to an occupational sensitizer or to a common inhaled allergen.11 A similar corticosteroid-responsive cough syndrome has been reported by Fujimura et al12 and has been given the diagnostic label atopic cough. This condition has been defined as an isolated chronic cough that is associated with no variable airflow obstruction or airway hyperresponsiveness and objective evidence of atopy as defined by one or more of the following: blood or sputum eosinophilia; elevated total or specific IgE levels; or positive skin test results. Whether nonasthmatic eosinophilic bronchitis and atopic cough represent distinct clinical entities is unclear.13 The main features and differences among nonasthmatic eosinophilic bronchitis, cough-variant asthma, classic asthma, and atopic cough are summarized in Table 1 .
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A 2-year prospective study of chronic cough,2 was reported in which induced sputum was performed in all patients in whom the diagnosis remained unclear after simple clinical assessment and a methacholine inhalation test. Ninety-one patients with chronic cough were identified among 856 referrals. A diagnosis leading to a successful treatment was reached in 85 of cases (93%). Nonasthmatic eosinophilic bronchitis using the above definition was identified in 12 patients (13.2%), representing 30% of those who had undergone sputum induction.
| Recommendations |
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2. In patients with chronic cough with normal chest radiograph findings, normal spirometry findings, and no evidence of variable airflow obstruction or airway hyperresponsiveness, the diagnosis of nonasthmatic eosinophilic bronchitis as the cause of the chronic cough is confirmed by the presence of an airway eosinophilia, either by sputum induction or bronchial wash fluid obtained by bronchoscopy, and an improvement in the cough following corticosteroid therapy. Level of evidence, expert opinion; benefit, substantial; grade of recommendation, E/A
| Treatment |
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There are no data currently available to guide the choice of which inhaled corticosteroid should be used for the treatment of nonasthmatic eosinophilic bronchitis, at which dose, and for how long. The efficacy of inhaled corticosteroids remains to be determined in placebo-controlled randomized trials. Very occasionally, treatment with oral corticosteroids are required to control symptoms and eosinophilic inflammation.23
Although there may be thickened basement membrane and other changes to suggest airway remodeling,24 it remains unclear whether therapy for nonasthmatic eosinophilic bronchitis should be discontinued when symptoms resolve. The role of other potential therapeutic agents such as antihistamines and antileukotrienes needs to be fully explored.
| Recommendations |
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4. For patients with chronic cough due to nonasthmatic eosinophilic bronchitis, the first-line treatment is inhaled corticosteroids (except when a causal allergen or sensitizer is identified [see recommendation 5]). Level of evidence, low; benefit, substantial; grade of recommendation, B
5. For patients with chronic cough due to nonasthmatic eosinophilic bronchitis, when a causal allergen or occupational sensitizer is identified, avoidance is the best treatment. Level of evidence, expert opinion; benefit, substantial; grade of recommendation, E/A
6. For patients with chronic cough due to nonasthmatic eosinophilic bronchitis, if symptoms are persistently troublesome and/or the natural history of eosinophilic airway inflammation progresses despite treatment with high-dose inhaled corticosteroids, oral corticosteroids should be given. Level of evidence, expert opinion; benefit, substantial; grade of recommendation, E/A
| Pathogenesis |
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A detailed comparative immunopathologic study of nonasthmatic eosinophilic bronchitis and asthma has been reported. Both conditions were associated with a similar degree of sputum,1925 BAL fluid,1926 and biopsy eosinophilia, and a similar degree of basement membrane thickening1924 in bronchial biopsy specimens, suggesting that the sites within the bronchial tree were similar. Similarly, asthma and nonasthmatic eosinophilic bronchitis were associated with increased sputum concentrations of the important effector mediators cysteinyl-leukotrienes and eosinophilic cationic protein.24 Interestingly, histamine and prostaglandin D2 sputum concentrations are only increased in patients with nonasthmatic eosinophilic bronchitis, suggesting that the activation of mast cells in superficial airway structures is a particular feature of this condition and raising the possibility that the localization of activated mast cells might differ in patients with asthma and nonasthmatic eosinophilic bronchitis. In support of this, mast cell numbers in bronchial brushing samples were increased in patients with nonasthmatic eosinophilic bronchitis compared to those with asthma,26 and mast cell numbers in airway smooth muscle were increased in patients with asthma but not in those with nonasthmatic eosinophilic bronchitis.24 Furthermore, airway smooth muscle mast cell numbers inversely correlated with airway hyperresponsiveness. Thus, a key factor determining the different functional association of airway inflammation in patients with nonasthmatic eosinophilic bronchitis and asthma might be the microlocalization of mast cells with a predominant airway smooth muscle infiltration (Fig 1 ), resulting in airway hyperresponsiveness and variable airflow obstruction, and an epithelial infiltration producing bronchitis and cough. The specific role of the mast cell in the bronchial epithelium of patients with nonasthmatic eosinophilic bronchitis and its interactions with cough sensory afferents needs further study.
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| Natural History |
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A case has been reported23 of a patient in whom, over a 2-year period, fixed airflow obstruction developed. The patients cough improved with inhaled corticosteroid therapy, but the sputum eosinophilia persisted. Several studies931 have observed that 30 to 40% of patients with COPD without a history of asthma and no bronchodilator reversibility have sputum evidence of an airway eosinophilia. This observation provides one possible explanation for the presence of eosinophilic airway inflammation in some patients with COPD without apparent preexisting asthma in that nonasthmatic eosinophilic bronchitis may in some circumstances be a prelude to COPD. Progressive irreversible airflow obstruction may occur due to remodeling of the airway secondary to persistent eosinophilic airway inflammation in the presence of inadequate corticosteroid therapy. If this is true, it has important implications in the early diagnosis and successful treatment of nonasthmatic eosinophilic bronchitis. Subsequent studies should be able to further define the natural history of this easily treatable condition.
| Conclusions |
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| Summary of Recommendations |
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2. In patients with chronic cough with normal chest radiograph findings, normal spirometry findings, and no evidence of variable airflow obstruction or airway hyperresponsiveness, the diagnosis of nonasthmatic eosinophilic bronchitis as the cause of the chronic cough is confirmed by the presence of an airway eosinophilia, either by sputum induction or bronchial wash fluid obtained by bronchoscopy, and an improvement in the cough following corticosteroid therapy. Level of evidence, expert opinion; benefit, substantial; grade of recommendation, E/A
3. In patients with chronic cough due to nonasthmatic eosinophilic bronchitis, the possibility of an occupation-related cause needs to be considered. Level of evidence, expert opinion; benefit, substantial; grade of recommendation, E/A
4. For patients with chronic cough due to nonasthmatic eosinophilic bronchitis, the first-line treatment is inhaled corticosteroids (except when a causal allergen or sensitizer is identified [see recommendation 5]). Level of evidence, low; benefit, substantial; grade of recommendation, B
5. For patients with chronic cough due to nonasthmatic eosinophilic bronchitis, when a causal allergen or occupational sensitizeris identified, avoidance is the best treatment. Level of evidence, expert opinion; benefit, substantial; grade of recommendation, E/A
6. For patients with chronic cough due to nonasthmatic eosinophilic bronchitis, if symptoms are persistently troublesome and/or the natural history of eosinophilic airway inflammation progresses despite treatment with high-dose inhaled corticosteroids, oral corticosteroids should be given. Level of evidence, expert opinion; benefit, substantial; grade of recommendation, E/A
| References |
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