Obstructive sleep apnoea: a cause of chronic cough

A 52-year-old financial advisor was referred by his general practitioner with a 3-month history of productive cough. He described a severe barking cough that occurred both in the day and night time and was exacerbated by lying flat, strong odours and smoky atmospheres. He was prescribed multiple courses of antibiotics, which were unhelpful. He also complained of mild dyspnoea on climbing hills but no wheezing. He had longstanding left nasal congestion without post-nasal drip following a broken nose in childhood and mild symptoms of gastro-oesophageal reflux. He had been diagnosed with hypertension and hypercholesterolaemia two years previously for which he was prescribed Bendroflumethiazide, Valsartan, Doxazoscin and Cervistatin. He was an ex-smoker and accumulated a 15 pack-year smoking history. His clinical examination and physical findings were normal. Initial spirometry and chest radiograph were within normal limits (Table 1). His cough was thought to be due to gastro-oesophageal reflux and rhinitis so he was started on a prolonged course of topical nasal steroids and high dose proton pump inhibitor. Methacholine airway challenge test, induced sputum eosinophil cell count, high resolution computerised tomography (HRCT) scan and echocardiogram arranged to investigate asthma, eosinophilic bronchitis, bronchiectasis and left ventricular dysfunction were all normal (Table 1).

On review 6 and 12 months later his symptoms of rhinitis and gastro-oesophageal reflux had resolved but his cough persisted. No explanation for the cough was found and he discharged back to his general practitioner. He was re-referred back to the clinic 3 years later with daytime somnolence, lethargy, apnoeas and cough. In retrospect, he had mild daytime somnolence and lethargy at the time of initial presentation. He was noted to have a small oropharynx on external examination. Polysomnography was arranged that was consistent with the diagnosis of obstructive sleep apnoea (Table 1). Nocturnal nasal continuous positive airway pressure (CPAP) therapy was commenced and he noticed an immediate improvement in cough and daytime somnolence. His cough resolved entirely within 6 weeks and he remains free of cough 12 months later. The initiation of CPAP therapy has also led to a reduction in anti-hypertensive medications and complete resolution of oxygen desaturation on repeat sleep study.

A 73 year-old housewife with an 18-month history of severe chronic cough was referred by her respiratory physician for a second opinion. The cough was predominantly dry, interfered with her daily activities and occasionally disturbed her sleep. She did not report other respiratory symptoms, postnasal drip or gastro-oesophageal reflux. Her past medical history consisted of diabetes, hypertension, atrial fibrillation and aorto-femoral bypass for peripheral vascular disease. Soon after the onset of cough, she was diagnosed as having severe obstructive sleep apnoea with full polysomnography after admitting to symptoms of daytime somnolence, snoring and disturbed sleep (Table 1). She could not be persuaded to try CPAP therapy or alternative options and was more concerned about the chronic cough. She was an ex-smoker and stopped smoking 13-years previously, accumulating a 40-pack year smoking history. Clinical examination and chest radiograph were normal. Spirometry was consistent with a moderate restrictive defect consistent with obesity. Treatment trials with inhaled corticosteroids, short and long acting bronchodilators and high dose proton pump inhibitors were unsuccessful. Nasendoscopy, Ear-Nose-Throat evaluation, echocardiogram (normal left ventricular function) and bronchoscopy were normal. She had marked impairment of quality of life secondary to chronic cough as assessed with the Leicester Cough Questionnaire (Figure 1) and increased cough frequency measured with the Leicester Cough Monitor, a 24-hour ambulatory automated cough detection monitor (Figure 2). [5‐7] She agreed to try CPAP therapy at a subsequent follow-up clinic. She was admitted for a CPAP titration study and a pressure of 12 cm H₂o abolished snoring and apnoeas. She noticed a significant improvement in cough at the end of the first week on CPAP therapy. There was an 80% reduction in objective cough frequency at 6-weeks (672 vs 141 coughs per 24-hours) and a significant improvement in cough specific quality of life (Improvement in LCQ total score 8.2 which was greater than the LCQ minimal important difference of 1.3; Figures 1 and 2). She was able to resume regular activities after improvement of her cough.

A 46-year-old nurse was referred by her occupational health physician with a 1-year history of productive cough. The cough occurred through the day and night and there were no specific triggers or associated symptoms. There were no symptoms of dyspnoea or wheeze. She did not complain of symptoms suggestive of rhinitis or gastro-oesophageal reflux. A trial of inhaled corticosteroids and nasal steroids were unhelpful. Her husband commented that she recently started snoring but he had not witnessed apnoeas. She complained of lethargy that was associated with mild somnolence. She had pneumonia in childhood but was unable to give further details. Her past medical history was otherwise unremarkable. She had never smoked and did not consume alcohol. On examination, she had evidence of retrognathia but was otherwise unremarkable. Chest radiograph and spirometry were within normal limits.

The initial differential diagnosis was cough secondary to asthma, eosinophilic bronchitis or bronchiectasis. Methacholine airway challenge test, induced sputum eosinophil cell count and HRCT were arranged and were normal (Table 1). Partial polysomnography (RM60 study: airflow, chest wall movement, oximetry, snoring, pulse) was subsequently arranged because of mild somnolence and snoring, which was highly suggestive of obstructive sleep apnoea. Nocturnal nasal CPAP therapy was commenced and she noticed an immediate improvement in cough, lethargy and somnolence. The cough resolved within 5 days and she remains free of cough 15 months later. Repeat sleep study indicates complete resolution of oxygen desaturation on CPAP.

A 63-year-old office worker with the police force was referred by his general practitioner with a 4-month history of chronic productive cough. The cough was severe, occurred both day and night time and was worse lying flat. There were no dyspnoea, wheeze or symptoms suggesting gastro-oesophageal reflux and rhinitis. He was an ex-smoker with less than 2 pack year smoking history and did not consume alcohol. His past medical history was unremarkable. Clinical examination, chest radiograph and spirometry were normal.

The cause of cough was not clear. Methacholine airway challenge test and induced sputum eosinophil cell count were normal (Table 1). At 4-month review he complained of snoring and daytime somnolence. A pulse oximetry sleep study was arranged which was consistent with a diagnosis of obstructive sleep apnoea. The cough and sleepiness improved significantly with nocturnal nasal CPAP after 2 days and the cough resolved completely 3 months later. At 15-month review after initiation of CPAP therapy, the patient does not complain of cough or somnolence.