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Chronic Idiopathic Cough^*

A Discrete Clinical Entity?

^* From Airway Disease Section, National Heart & Lung Institute, Imperial College, London, UK.

Correspondence to: Rubaiyat A. Haque, MBBS, Airways Disease Section, National Heart & Lung Institute, Imperial College, Dovehouse St, London, SW3 6LY, UK; e-mail: r.haque{at}imperial.ac.uk

Study objectives: Despite the success of specialist cough clinics, there is increasing recognition of a subgroup of chronic coughers in whom a diagnosis cannot be made even after thorough, systematic investigation. We call this condition chronic idiopathic cough (CIC). The aim of this study is to compare the clinical characteristics of CIC patients with those of coughers in whom a diagnosis has been established (non-CIC) to see if there is a recognizable clinical pattern that distinguishes CIC from non-CIC.

Design: Retrospective analysis of the medical records of chronic cough patients.

Setting: The Royal Brompton Hospital Chronic Cough Clinic, London.

Patients: One hundred patients with chronic cough referred to the Royal Brompton Hospital Cough Clinic between October 2000 and February 2004.

Results: Seventy-one percent of all patients were female. Median age was 57 years (range, 19 to 81 years), with a median duration of symptoms of 48 months (range, 2 to 384 months). The primary diagnoses were CIC (42%), postnasal drip syndromes (22%), gastroesophageal reflux disease (16%), asthma (7%), and others (13%). In CIC patients, the median age at referral, age at onset of cough, and proportion of females did not differ significantly from non-CIC patients. CIC patients had a longer median duration of cough (72 months vs 24 months, p = 0.002), were more likely to report an upper respiratory tract infection (URTI) as the initial trigger of their cough (48% vs 24%, p = 0.0014), and had a significantly lower cough threshold in response to capsaicin (log concentration of capsaicin required to induce five or more coughs, – 0.009 vs 0.592, p = 0.032) than non-CIC patients.

Conclusions: Patients with CIC commonly describe a URTI that initiates their cough, which then lasts for many years, and they demonstrate an exquisitely sensitive cough reflex. We believe that CIC may be a distinct clinical entity with an as-yet unidentified underlying pathology.

Key Words: chronic cough • etiology • idiopathic cough

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