LONDON - One in three patients with sleep disordered breathing (SDB) suffers from unexplained chronic cough, suggests a recent study published in the European Respiratory Journal.

According to Dr S. Birring of the Department of Respiratory Medicine, King's College Hospital, London, chronic cough is not only very common in patients with sleep disordered breathing, but  it can be the sole presenting symptom of the syndrome.

Moreover, diagnosing chronic cough associated with sleep disordered breathing may offer more than just a “label”. Chronic cough may well respond to specific therapy such as continuous positive airway pressure (CPAP).

Researchers recruited 108 patients attending a specialised sleep centre because of sleep-related breathing disorders.

In search of patients with unexplained chronic cough, however, about half of the patients had to be  excluded from the study, as they had presented with possible causes for their cough, such as smoking, a  history of  respiratory disease, medications with coughing as known side-effects such as angiotensin converting enzyme (ACE) inhibitors, or a recent upper respiratory tract infection.

The remaining 55 subjects were invited to complete a questionnaire that sought to identify chronic cough or other respiratory symptoms.
In parallel, Dr Birring and his colleagues carried out comprehensive overnight testing for sleep disorders, which included an electroencephalogram, electromyogram and electrooculogram. They also measured nocturnal blood oxygen saturation.

One in three patients with SDB suffered from chronic cough, 61% of whom were women. Cough was also frequently associated with symptoms of nocturnal heartburn and rhinitis.

The authors hypothesise that gastro-oesophageal reflux disease, a disorder associated with both chronic cough and SDB, may be the common denominator. The negative intrathoracic pressure associated with inspiratory efforts against an upper airway resistance in obstructive sleep apnoea may lead to regurgitation of gastric contents. In addition to these mechanical factors, the airway inflammation seen with obstructive sleep apnoea, contributes to causing chronic cough. The association seen with rhinitis would support this.

“In conclusion,” write the researchers, “chronic cough is prevalent in patients with SDB and impacts on their quality of life. SDB cough is not well recognised by physicians and it is possible that some patients referred to specialist clinics for investigation of cough are misdiagnosed. Preliminary reports suggest it responds well to specific therapy for SDB.”

Reference:
Chan KK. Et al. Eur Respir J. 2010 Feb;35(2):368-72.