Cough is a nonspecific reaction to irritation anywhere from the pharynx to the lungs. Cough can be divided into acute self-limiting cough, lasting less than 3 weeks, or chronic persistent cough, which usually lasts for more than 8 weeks. Cough lasting for an intermediate period of 3-8 weeks is called subacute cough.
- Chronic cough lasting for more than 8 weeks is common in the community. Chronic cough is reported by 10-20% of adults.
- Risk factors include atopy and smoking. Cough may be work-related and a thorough occupation history is very important in assessment.
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The cough reflex is triggered by mechanical or inflammatory changes or irritants in the airways. The afferent pathway is via the vagus nerve to respiratory neurones termed the 'cough centre' in the brainstem. Higher cortical centres also control the cough. Chronic cough tends to be inhibited during sleep.
Chronic cough is often associated with bronchial hyperreactivity (bronchial hyper-responsiveness), which can persist in the absence of the initiating cough event. Bronchial hyper-responsiveness is defined as a state of increased sensitivity to a wide variety of airway narrowing stimuli, eg exercise, dry or cold air, hypertonic or hypotonic aerosols. It occurs in asthma and chronic obstructive pulmonary disease (COPD), but also can occur in the absence of lung disease.
Most cases of troublesome cough reflect the presence of an aggravant (asthma, drugs, environmental, gastro-oesophageal reflux, upper airway pathology) in a susceptible individual. The most common causes of chronic cough, other than smoking in adults, are postnasal drip, asthma, and gastro-oesophageal reflux disease (GORD).
- Smoking (active or passive).
- Asthma (and its variants, ie cough variant asthma, eosinophilic bronchitis) - all of which are steroid-responsive.
- Postnasal drip.
- Environmental pollution, especially PM10 particulates (particles of 10 micrometres or fewer).
- Angiotensin-converting enzyme (ACE) inhibitors.
- Occupational exposure to irritants (including farm workers, workers exposed to hot acidic conditions in a bottle factory, and workers exposed to hot chilli peppers).
- Whooping cough - in young adults and may be more common than previously supposed.
Less common causes
- Cardiovascular - left ventricular failure, pulmonary emboli, aortic aneurysm.
- Chronic infections - bronchiectasis, tuberculosis, cystic fibrosis, lung abscess.
- Postinfectious cough - may be more likely following infection with Mycoplasma pneumoniae, chlamydial pneumonia and whooping cough.
- Parenchymal lung diseases - interstitial lung fibrosis, emphysema, sarcoidosis.
- Tumours - lung cancer, metastatic carcinoma, lymphoma, mediastinal tumours, benign tumours.
- Upper airway conditions (other than chronic rhinitis, above) - chronic tonsil enlargement, obstructive sleep apnoea, chronic snoring, irritation of external auditory meatus. Laryngeal problems are increasingly recognised as being part of chronic cough.
- Foreign body in large airways - recurrent aspiration, inhaled foreign body, endobronchial sutures.
- Rarely, cough may be due to cardiac arrhythmias.
- Cough only when supine - may be due to collapse of large airways.
- Diffuse panbronchiolitis - a recognised cause in Japan, responds to low-dose macrolide antibiotics (but resistant to steroids).
- Chronic cough may be a presentation of a complex involuntary tic (eg as sometimes seen in Tourettes Syndrome)
- One small study suggested that vitamin B12 deficiency contributes to chronic cough (perhaps due to sensory neuropathy).
- Idiopathic or psychogenic - a diagnosis of exclusion.
- Nature of cough - dry, sputum, blood.
- Pattern of cough - duration, frequency, nocturnal, association with eating or talking.
- History of atopy?
- Smoking and occupation.
- Drugs (especially ACE inhibitors).
- Red flags (see box).
- Systemic signs, eg fever, weight loss, clubbing, lymphadenopathy.
- Upper airway signs, eg hoarseness, nasal speech.
- Focal chest signs.
- Cardiovascular system.
- Peak expiratory flow rate.
|Common causes of cough and their symptoms|
|Asthma||Gastro-oesophageal reflux disease (GORD)||Postnasal drip syndrome|
Initial assessment, investigation and treatment in primary care
Studies have shown a low frequency of serious pulmonary conditions in patients who have an isolated chronic dry cough and normal physical examination, CXR and spirogram.
A suggested strategy for primary care, using the principle of diagnosis by "test of treatment" is:
- History and examination. Look for 'red flags' which require early investigation (see box).
- Assuming there are no red flags, obvious cause or abnormal signs on examination, proceed as follows:
- For smokers, initial investigations are CXR and spirometry, with advice to stop smoking. If smoking is the cause, cough should improve within 8 weeks of smoking cessation.
- For non-smokers, if taking an ACE inhibitor, trial of stopping/replacing this drug. ACE inhibitor-induced cough should improve within 4 weeks of stopping the drug. Then consider CXR and spirometry (or serial peak flow measurements, if spirometry unavailable).
- Assess likely diagnosis and refer/trial of treatment accordingly:
- Serious disease? - refer to chest clinic.
- Asthma? - trial of steroids (inhaled steroids for 8 weeks, or oral steroids for 2 weeks).
- Gastro-oesophageal reflux disease (GORD)? - trial of high-dose proton pump inhibitors (may require up to 12 weeks for improvement).
- Postnasal drip syndrome? - trial of antihistamines or nasal steroids.
- Blood tests - FBC (infection, eosinophilia), ESR/CRP (infection, malignancy, connective tissue disorders).
- Assess for other contributing factors, eg reflux disease, rhinitis, occupation (there may be more than one factor causing chronic cough). Try treating these (or removing the cause, if occupational) for a limited period to observe response.
- Assess for eosinophilic airway inflammation - by induced sputum analysis or trial of steroids (prednisolone 30 mg daily for two weeks).
Possible further investigations include:
- Bronchial provocation testing (methacholine or histamine) - positive result supports diagnosis of asthma, but cough may be steroid-responsive even if negative.
- Induced sputum analysis.
- Bronchoscopy - if inhalation of a foreign body is suspected, or where common causes have been excluded.
- Echocardiogram or other cardiac investigations - if a cardiac cause is suspected clinically.
- 24-hour ambulatory oesophageal pH testing and/or oesophageal manometry.
- Radiology of sinuses, eg CT or MRI scanning.
- High-resolution CT scan of thorax - but there is low diagnostic yield in this scenario.
Assessment of response:
- May use a cough visual analogue scale, the Leicester Cough Questionnaire or a capsaicin challenge.
- Treat the underlying cause(s), if possible (see 'Initial assessment, investigation and treatment in primary care' and 'Further assessment' sections, above).
- A "trial of treatment" strategy is often appropriate, ensuring that each treatment is used for a sufficient time, eg eight weeks for inhaled steroids, 12 weeks for anti-reflux treatment.
- Smoking cessation; avoid exposure to irritants.
- If initial management is unsuccessful, referral to secondary care may be required. This may involve a chest physician, ENT specialist and/or gastroenterologist, depending on the individual context.
Symptomatic treatment of cough
There are various drugs which may partially suppress cough, although the cough reflex is exceedingly difficult to abolish. Also, there is a lack of evidence for the efficacy of most antitussive drugs. British Thoracic Society guidelines state: "There are no effective treatments controlling the cough response per se with an acceptable therapeutic ratio."
Possible drug treatments include:
- Opiates - codeine; pholcodine (fewer side-effects). Low-dose morphine can be effective (eg 5 mg orally), but side-effects limit its use. Morphine or diamorphine at higher doses may be used for severe, distressing cough in palliative care.
- Dextromethorphan (an ingredient in many over-the-counter preparations) - fewer side-effects than codeine.
- Mucolytic agents, eg erdosteine.
- Anticholinergics, eg ipratropium bromide.
- There have been case reports of benefit with centrally acting drugs, eg amitriptyline, paroxetine, gabapentin, and carbamazepine.
- GABAB agonists, eg baclofen.
- Nicotine may have a cough suppressant effect; nicotine replacement may reduce cough in the subacute period following cessation of smoking.
- N-acetylcysteine used with fluticasone and salmeterol was helpful in one study (of patients exposed to sulfur mustard ('mustard gas')).
- Speech therapy or physiotherapy has shown benefit in some studies.
- Honey, lozenges, and demulcent cough preparations containing syrup or glycerol, are commonly used by patients with cough. There is little evidence on their effectiveness, and most studies have only assessed their use for acute cough in children.
Further reading & references
- ERS guidelines on the assessment of cough, European Respiratory Society (2007)
- Irwin RS, Baumann MH, Bolser DC, et al; Diagnosis and management of cough executive summary: ACCP evidence-based clinical practice guidelines. Chest. 2006 Jan;129(1 Suppl):1S-23S.
- Smith J, Woodcock A, Houghton L; New developments in reflux-associated cough. Lung. 2010 Jan;188 Suppl 1:S81-6. Epub 2009 Dec 19.
- Chang AB, Lasserson TJ, Gaffney J, et al; Gastro-oesophageal reflux treatment for prolonged non-specific cough in children Cochrane Database Syst Rev. 2011 Jan 19;(1):CD004823.
- Chung KF, Pavord ID; Prevalence, pathogenesis, and causes of chronic cough. Lancet. 2008 Apr 19;371(9621):1364-74.
- Morice AH, McGarvey L, Pavord I; Recommendations for the management of cough in adults. Thorax. 2006 Sep;61 Suppl 1:i1-24.
- Barraclough K; Chronic cough in adults. BMJ. 2009 Apr 24;338:b1218. doi: 10.1136/bmj.b1218.
- Pavord ID, Chung KF; Management of chronic cough. Lancet. 2008 Apr 19;371(9621):1375-84.
- Tokayer AZ; Gastroesophageal reflux disease and chronic cough. Lung. 2008;186 Suppl 1:S29-34. Epub 2008 Jan 24.
- Ross AM; Article misses the point about pertussis. BMJ rapid responses, 26 May 2009.
- Ryan NM, Vertigan AE, Gibson PG; Chronic cough and laryngeal dysfunction improve with specific treatment of cough Cough. 2009 Mar 17;5:4.
- Stec SM, Grabczak EM, Bielicki P, et al; Diagnosis and management of premature ventricular complexes-associated chronic Chest. 2009 Jun;135(6):1535-41. Epub 2009 Mar 24.
- Duncan KL, Faust RA; Tourette syndrome manifest as chronic cough. Int J Pediatr Otorhinolaryngol. 2002 Aug 1;65(1):65-8.
- Bucca CB, Culla B, Guida G, et al; Unexplained chronic cough and vitamin B-12 deficiency. Am J Clin Nutr. 2011 Mar;93(3):542-8. Epub 2011 Jan 19.
- Morice AH, McGarvey L, Pavord I; Protocol for the evaluation of chronic cough in an adult. Thorax 2006;61(suppl_1):i1-i24.; ALGORITHM Part 1
- Morice AH, McGarvey L, Pavord I; Protocol for the evaluation of chronic cough in an adult; Part 2. Thorax 2006;61(suppl_1):i1-i24.; ALGORITHM Part 2
- Bolser DC; Pharmacologic management of cough. Otolaryngol Clin North Am. 2010 Feb;43(1):147-55, xi.
- Chung KF; Currently available cough suppressants for chronic cough. Lung. 2008;186 Suppl 1:S82-7. Epub 2007 Oct 2.
- British National Formulary; 62nd Edition (Sep 2011) British Medical Association and Royal Pharmaceutical Society of Great Britain, London
- Mulholland S, Chang AB; Honey and lozenges for children with non-specific cough. Cochrane Database Syst Rev. 2009 Apr 15;(2):CD007523.
|Original Author: Dr Colin Tidy||Current Version: Dr Naomi Hartree|
|Last Checked: 22/06/2011||Document ID: 574 Version: 24||© EMIS|
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