Cough: not always what it seems
At this time of year, our waiting rooms are full of patients coughing and sneezing, so it is no surprise to learn that cough is one of the most common reasons for a consultation. More surprising is that not all coughs are respiratory in origin
Cough is one of the most common symptoms presenting in primary care.1 Practice nurses are frequently asked to give advice, and have an important role to play in raising awareness of when a cough is self limiting and needs no intervention, and when it may be due to a more serious condition that warrants medical treatment or further investigation. However, a cough forms part of the presentation in a number of conditions and may have a respiratory or a non-respiratory cause. This article will look at some of the less common causes of cough, and aims to enhance nurses' knowledge, and confidence in offering appropriate advice.
ACUTE OR CHRONIC?
Coughs are generally classified in association with their duration. An acute cough lasts less than 3 weeks. A sub-acute cough lasts 3 to 8 weeks — this is the type of cough that often lingers after a cold or other respiratory infection has resolved. Chronic cough generally refers to coughs lasting for more than 8 weeks.2 Acute coughs are extremely common and can have a number of causes (box 1), but in the vast majority of cases, they are due to viral upper respiratory tract infections that are usually self limiting, and generally resolve without any medical intervention. Chronic cough is often more difficult to evaluate, and while the symptom is often one of the key presenting features of a number of important chronic respiratory diseases, (Table 1) it can also be the sole presenting feature of a number of extra-pulmonary conditions.3 An estimated 40% of the population is believed to suffer from chronic cough.4
PATHOPHYSIOLOGY
A cough is part of the body's defence mechanism and serves to clear the airways of any potentially invading organism or substances and has an important role in preventing infection by blocking any potential foreign substances from gaining entry to the airways. Cough is a protective mechanism by which excess mucus and the noxious particles trapped in it are expelled from the airways Expulsion requires high intra-thoracic pressures against a closed glottis, which forces the opening of the glottis and expulsion of both mucus and foreign bodies.5
CAUSES
A chronic cough presents a challenge to clinicians but studies have shown that most episodes of chronic cough in adults are caused by postnasal drip syndrome (PND), cough variant asthma, or gastroesophageal reflux disease (GORD), which can occur alone or in combination with asthma.6 It is also worth mentioning that one of the commonest causes of persistent cough is smoking, which appears to be dose related (i.e. dependent on the amount smoked) and with successful smoking cessation, patients often say that their cough changes in character and reduces in frequency.3 Assessment of the patient should also take note of any worrying features (red flags, Table 2) which will require an urgent review by a GP and further assessment and investigation.
GASTRO-OESOPHAGEAL REFLUX DISEASE
Chronic cough in association with GORD has long been recognised, although it is unclear whether the two symptoms occur together merely by chance or whether one symptom causes the other. Patients with GORD have an increased cough reflex sensitivity,7 and it is thought that a cough in association with GORD may be induced by aspiration of the gastric contents into the larynx and trachea-bronchial tree.8 The clinical features of GORD-related cough include heartburn, regurgitation, and/or worsening of cough after foods or medications known to decrease lower oesophageal sphincter-pressure.9 However, while classic GORD symptoms are present in 6—10% of patients with chronic cough, the condition is clinically silent in up to 75% of patients with GORD-related cough.10 There are a number of therapies available for the treatment of heartburn, and studies have shown that antireflux therapy produces an improvement in chronic reflux cough in 75—100% of cases.11
COUGH VARIENT ASTHMA
Cough variant asthma is a form of asthma in which the only sign or symptom is a chronic cough. The true prevalence is unknown because of difficulties in assessment and diagnosis based on the fact that both physical examination and laboratory results are often completely normal.12 Symptoms include a cough which occurs nocturnally, after exercise, or after exposure to an allergen, and suspicion should be raised when the patient presents with an isolated cough where there is no evidence of asthma or variable airflow obstruction either from the history or the clinical findings. Because of the absence of other typical symptoms of asthma, it is recommended that any patient with a non-productive, nocturnal cough lasting more than two weeks, should receive an empiric trial of treatment: symptoms have been found to respond well to corticosteroids.13 The natural history of cough variant asthma is variable, with a significant proportion of patients followed over time going on to develop the classic signs and symptoms of asthma, whereas for others, the cough resolves without need for further intervention or treatment.14
MEDICATION-INDUCED COUGH
Cough is a common side effect of angiotensin converting enzyme inhibitors (ACE inhibitors) used in the treatment of hypertension and heart failure, affecting an estimated 15% of patients taking this class of drugs.15 If the problem does develop there appears to be a variable period of onset from patient to patient. The underlying cause of the cough is attributed to an alteration in the sensitivity of the cough reflex, but this usually returns to normal once the treatment is stopped or the patient is switched to an alternative. However, again it is unclear how long it make take for the cough to resolve, as it varies from patient to patient. The most commonly used alternative to an ACE inhibitor is an angiotensin II receptor blocker (ARB), which is less likely to cause a cough because of its different site of action. ARBs displace angiotensin II from the angiotensin I receptor, antagonising angiotensin II-induced vasoconstriction,16 which contributes to their blood pressure lowering effect.
POST NASAL DRIP
The most common cause of chronic cough is postnasal drip syndrome (PND), with onset of symptoms usually following viral infection of the upper respiratory tract.17 Symptoms develop when secretions from the nose or paranasal sinuses drain into the pharynx, irritating the throat. Symptoms may often be vague and non-specific, making a diagnosis difficult, and there are no specific tests available either to quantify the secretions or to prove that they are directly responsible for causing the cough. Patients may complain of a tickling feeling or a sensation of something dripping at the back of the throat, with constant attempts to clear the throat having minimal effect. Diagnosis is made more difficult by the fact that other conditions such as seasonal or allergic rhinitis and chronic sinusitis have similar symptoms, and also result in post nasal drip and chronic cough. Treatment is generally with a trial of a first generation antihistamine (e.g. piriton) and a decongestant such as pseudo-ephedrine.17 If there is improvement or resolution of symptoms treatment can be continued, although any improvement may take several weeks or even months.18 If no improvement is seen, an alternative cause for the cough should be sought.
CARDIAC PROBLEMS
Heart failure can also be a cause of cough, especially during periods of fluid overload. The cough associated with left ventricular failure (LVF) can be non-productive but is commonly associated with sputum that has a pink, frothy appearance and that may be present in copious amounts in patients with severe disease.19 The cough is often most troublesome at night when the patient lies down, resulting in difficulty breathing and sleep disturbance. Sleeping supported by several pillows may be helpful.
CONCLUSION
The majority of coughs cause few problems and will resolve within 3 weeks or so, often without the need for medical advice or treatment. However, when symptoms persist, a thorough history and assessment is needed to determine the cause of the cough: it may arise as a result of a chronic respiratory problem but in other cases it will be non-respiratory in origin. Awareness of other causes of persistent chronic cough will enable nurses to offer appropriated advice, and by having the skills to recognise when further assessment is needed, they can play a part in improving quality of life for those affected.
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