Cough is a common symptom, and one of the most frequent reasons for consulting a GP. Although the majority of coughs are short-lived, self-limiting and benign, many are not. Identifying those cases that represent potentially life-limiting illness can be a challenge.
What are the potential serious causes of cough?
The potentially serious causes of cough include:
- Lung cancer.
- Idiopathic pulmonary fibrosis, and other interstitial lung diseases, including sarcoidosis.
All of these can lead to death or significant morbidity.
However, the most common cause of cough is upper respiratory tract viral infection. Other frequent culprits include angiotensin-converting enzyme therapy (even after years of treatment), chronic sinusitis, and gastroesophageal reflux (although usually in the context of typical dyspepsia symptoms). A small proportion of chronic coughs are unexplained, perhaps due to cough reflex hypersensitivity.
Red flags can be split into risk factors and associated features.
- Increases the risk of almost all respiratory diseases. This applies for tobacco, cannabis, and other substances.
- At least 75% of patients with lung cancer worldwide are current or ex-smokers. Around 50% of lifelong smokers develop COPD. Smoking is not only a risk factor for pneumonia, but also for more severe forms of the disease.1
- The incidence of lung cancer starts to rise steeply after the age of 50. COPD relates to lifetime duration of smoking, while asthma is more common at a younger age. Pneumonia is most common in the very young and elderly.
- Environmental exposures
- Any new prolonged respiratory symptom should prompt enquiry of occupation and hobbies. Asthma can be both caused and exacerbated by exposures at work and is the most common occupational lung disease. Animal handlers, bakers, chemical workers, timber workers and welders are among those at risk.
- Previous asbestos exposure Increases the risk of lung cancer, mesothelioma and pulmonary fibrosis (asbestosis). Asbestos exposure is usually distant in time and may have been forgotten or not previously acknowledged. Occupations associated with asbestos include plumbing, carpentry, building, and electrical work.
- Hypersensitivity pneumonitis is a rare cause of cough, caused by prolonged inhalation of dusts and fumes originating from many sources including solder, metal-working fluid, birds, and mouldy hay.
- Atopy (eczema, allergic rhinitis)
- Increases the risk of asthma.
- Family history
- Most relevant for asthma and cystic fibrosis.
- Risk factors for TB
- Around 80% of cases of tuberculosis in England were born in a high TB-incidence country, or have at least one other social risk factor (e.g. previous imprisonment, homelessness or illicit drug use).2
Signs and symptoms:
Particularly in the context of the above risk factors and cough, associated red flag symptoms and signs for significant disease include:
- Weight loss.
- New coughs lasting over three weeks.
- Unexplained haemoptysis, particularly if recurrent or persisting.
- Night sweats.
- Finger clubbing.
- Superior vena cava syndrome (swelling, plethora and venous distension of the face, upper chest and arms).
- Acute hypoxia, tachypnoea, or signs of sepsis.
A chest x-ray is a very simple and useful test that should be considered for any patient with new or unexplained respiratory symptoms.
The test will be abnormal in most cases of pneumonia, pulmonary TB, bronchiectasis, and pulmonary fibrosis. In COPD the chest x-ray is also frequently characteristic.
However, a single chest x-ray may miss 25% of lung cancers.3 The definitive test to exclude lung cancer is CT of the chest, and should be considered with ongoing clinical concerns despite a normal chest x-ray, especially in those with a significant smoking history over the age of 50. GPs in some regions of the UK now have direct access to chest CT scanning, but an alternative is a two-week wait referral to the local lung cancer service to ensure rapid specialist review.
For cough relating to asthma, the most useful single diagnostic test is probably FeNO measurement – a marker of eosinophilic airway inflammation. If elevated, FeNO predicts the response to inhaled or oral corticosteroids. However other diagnostic tests for asthma are more generally accessible in primary care. These include serial diurnal peak flow home measurements and spirometry with bronchodilator reversibility testing, although both can be normal, particularly in cough-variant asthma. Obstructive spirometry that fails to reverse to normal with bronchodilator is required for a diagnosis of COPD.
For pulmonary tuberculosis, the most useful diagnostic test is sputum microbiology, specifically requesting mycobacterial stains and TB culture. Three samples taken at different times, with at least one in the early morning, maximises the yield.
What action needs to be taken?
This partly depends on the acuity of the presentation and the severity of the illness. Pneumonia can be a medical emergency requiring immediate antibiotic treatment and hospitalisation. Severe acute exacerbations of COPD and asthma similarly require urgent action including oral corticosteroids and hospital-level care.
With possible lung cancer, delays in investigation and treatment of several weeks or more can make significant differences in the final outcome. NHS hospitals are bound by national targets to see suspected cases of the disease within two weeks of referral from primary care and diagnose and start treatment within 62 days. As of 2020 the target time to diagnosis is due to be set at 28 days from referral.
Non-acute asthma also needs a diagnosis and effective treatment as soon as possible to prevent significant morbidity, lost workdays, and the potential for acute deterioration with the risk of death. Early interventional following an early diagnosis of COPD can also make a substantial difference in altering the course of the disease.
Following the chest x-ray, suspected bronchiectasis and interstitial lung disease should be referred routinely to a general or specialist respiratory clinic, depending on local services, for a diagnosis and management plan.
Suspected pulmonary tuberculosis should be referred within days to outpatient secondary care respiratory or infectious diseases services, preferably following collection of sputum samples. To limit potential disease transmission, patients should be advised to stay off work and limit social mixing until specialist evaluation. Patients with pulmonary TB only need hospital admission if significantly unwell or for strong social indications.
All patients who smoke should be strongly encouraged and supported to stop, regardless of symptoms.
Most people with chronic cough, a normal chest x-ray, and no red flag features can probably be managed in primary care.
Dr Richard Turner is a respiratory consultant at Charing Cross Hospital, Imperial College Healthcare NHS trust.