xRead - Globus and Chronic Cough (April 2024)

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Rouadi et al. World Allergy Organization Journal (2022) 15:100649 http://doi.org/10.1016/j.waojou.2022.100649

diagnosis in chronic cough. 88 In a stepwise diagnostic approach, an initial abnormal lung function testing suggests CA or COPD; normal testing is inclusive of CVA, NAEB, or chronic bronchitis (Fig. 1B). The absence of bronchial hyperreactivity to methacholine or mannitol 89 challenge in patients with seemingly normal physical examination and spirometry fi ndings raises suspicion of NAEB. 90 Similarly, a negative airway responsiveness can exclude CVA. 55 Of importance, a BCT is contra-indicated if immedi ate spirometry is abnormal. Fractional exhaled nitric oxide (FeNO) mea surement 43 for airway eosinophilia can also be helpful. 38 However, its use as a biomarker of eosinophilic airway in fl ammation and, by inference, steroid responsiveness, requires further elucidation. This is due to variable correlation between FeNO and airway eosinophilia as measured in induced sputum, bronchoalveolar lavage, or bronchial biopsies. 91 – 97 Notwithstanding, low FeNO is valuable in determining absence of eosinophilic airway in fl ammation 91 , 98 , 99 keeping in mind that the test predictive values (positive or negative) are dependent on the prevalence of eosinophilic airway in fl ammation in the tested population, and hence cannot be generalized. The role of FeNO in chronic cough is less clear. FeNO can generally assist in identifying subgroups with asthma, CVA and NAEB as potential causes of chronic cough 59 , 100 – 103 (Table 1). More precisely, it has been reported FeNO values below 30 ppb can reliably « rule out » asthma as a cause of chronic cough, 104 but higher values do not necessarily « rule it in » 105 . Others suggested FeNO can diagnose asthma or CVA as etiological factors in chronic cough with moderate accuracy at optimal cut-off values be tween 30 and 40 ppb. 105 A metanalysis revealed a relatively high (0.85) speci fi city of FeNO in predicting asthma in adults patients with chronic cough despite lack of consensus on cut-off levels for the diagnosis. 59 In comparison, FeNO diagnostic accuracy in predicting eosinophilic bronchitis (EB) in nonasthmatic chronic cough is lower compared to CVA which questions its utility in the former group. 59 Notwithstanding, it has been Table 1. Comparative analysis of ancillary testing and pharmacologic response in cough-phenotypic traits originating from the lower airways. CA, classic asthma; COPD, chronic obstructive pulmonary disease; CVA, cough variant asthma; FeNO, fractional exhaled nitric oxide; ICS, inhaled corticosteroids; LTRA, leukotriene receptor antagonist; NAEB, non asthmatic eosinophilic bronchitis CVA Normal Present or Borderline 30 – 40 ( þ )ve ( þ )ve ( þ )ve ( þ )ve ( )ve COPD Abnormal Present NA ( þ )ve ( þ )ve Not fully established

Spirometry 41 Therapeutic response 41,42,44 – 49 Bronchodilators ICS LTRAs CA Abnormal Present 30 – 40 ( þ )ve ( þ )ve ( þ )ve ( þ )ve NAEB 118 Normal Absent 22.5 – 31.7 ( þ )ve ( )ve ( þ )ve ( þ )ve Parental steroids Bronchial hyperresponsiveness (methacholine) 41,55,151 FeNO (ppb) 59,103,105