Chronic Cough

Cough is a non-specific 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.¹

The commonest causes of chronic cough other than smoking in adults are postnasal drip, asthma, and gastro-oesophageal reflux disease.² Respiratory tract infections, asthma, and gastro-oesophageal reflux disease are the most common causes of chronic cough in children. Foreign body aspiration should be considered in young children.

Almost everybody has had cough after a common cold, which typically lasts 1—3 weeks.¹ Community surveys suggest that most coughs related to upper respiratory tract infections resolve within 3 weeks. However cough takes several months to resolve in a small number of patients, especially following Mycoplasma pneumoniae, Chlamydophila pneumoniae (Chlamydia pneumoniae) and Bordetella pertussis infections. Persistent cough due to infection might be more likely in patients with pre-existing airway problems.³

• Chronic cough lasting for more than 8 weeks is common in the community.¹ Chronic cough is reported by 10-20% of adults.⁴
• It is more common in females and obese individuals.
• Cough accounts for 10% of respiratory referrals to secondary care.
• Risk factors include atopy and smoking. Cough may be work-related and a thorough occupation history is very important in assessment.

Most cases of troublesome cough reflect the presence of an aggravant (asthma, drugs, environmental, gastrooesophageal reflux,⁵ upper airway pathology) in a susceptible individual. The causes of chronic cough include:⁶

Adults

• Common: asthma, chronic obstructive pulmonary disease, gastro-oesophageal reflux disease, postnasal drip, cigarette smoking, exposure to cigarette smoke, exposure to environmental pollution, especially particulates, and other irritants including occupational exposure such as farm workers, workers exposed to hot acidic conditions in a bottle factory, and workers exposed to hot chilli peppers.³
• Less common: left ventricular failure, interstitial lung disease, pulmonary fibrosis, bronchiectasis, eosinophilic bronchitis, postinfectious, ACE inhibitors.
• Uncommon: chronic aspiration, lung cancer, metastatic carcinoma, irritable larynx, lymphoma, persistent pneumonia, psychogenic cough, pulmonary abscess, sarcoidosis, tuberculosis.

Children

• Common: asthma, gastro-oesophageal reflux disease, upper and lower respiratory tract infection, postinfectious cough, whooping cough, environmental exposures.
• Less common: foreign bodies in the airways or oesophagus (especially young children).
• Uncommon: aspiration, congenital abnormalities such as vascular rings, tracheobronchomalacia, pulmonary sequestration, mediastinal tumours, aspiration caused by poor coordination of swallowing or oesophageal dysmotility, immune deficiencies, cystic fibrosis, primary ciliary dyskinesia, and heart disease, psychogenic cough and tuberculosis.

• Most patients present with a dry or minimally productive cough. The presence of significant sputum production usually indicates primary lung pathology.
• Post nasal drip: nasal discharge, frequent need to clear throat, mucoid or mucopurulent secretions in posterior pharynx. X-ray of sinuses may show chronic sinusitis.
• Gastro-oesophageal reflux disease: may or may not be associated with heartburn or regurgitation. May respond to proton pump inhibitors.^9,10
• Asthma: wheezing, reduced pulmonary function tests. Should respond to two weeks of bronchodilators and inhaled steroids. Cough may wake patient during night.
• ACE inhibitor: common side effect and disappears on withdrawal of drug.
• Production of sputum with expectoration in the morning suggests chronic obstructive pulmonary disease.
• Dry cough lasting many weeks may suggest lung cancer. However non productive barking cough lasting for years may be of psychogenic origin.

Studies have shown a low frequency of serious pulmonary conditions in patients who have an isolated chronic dry cough and normal physical examination, chest x-ray and spirogram.³

• Blood tests include full blood count (infection, eosinophilia), ESR/CRP (infection, malignancy, connective tissue disorders).
• Chest X-ray and spirometry are mandatory for patients with chronic cough.⁴ Consider chest x-ray in patients with acute cough to exclude lung cancer for smokers and other patients with 'red-flag' features such as weight loss and fever.
• Tests suggesting the presence of eosinophilic airway inflammation, e.g. eosinophilic bronchitis, include a raised induced sputum eosinophil count and increased exhaled nitric oxide concentration,which are associated with success with corticosteroid therapy.³
• Bronchial hyperresponsiveness can be assessed by a bronchial challenge test, using metacholine or histamine.
• Bronchial provocation testing should be performed in patients without a clinically obvious aetiology. Cough sensitivity to capsaicin is probably the most widely used test for cough sensitivity.³
• If the cause of chronic cough remains unclear, high-resolution CT scanning of the chest and bronchoscopy may be required.
• Bronchoscopy should be undertaken in all patients with chronic cough in whom inhalation of a foreign body is suspected.
• Investigations of gastro-oesophageal reflux, including endoscopy.
• Investigations of upper respiratory tract and sinus causes, including CT/MRI scan.

Effective control of cough requires identification and management of the underlying cause, and also desensitisation of cough pathways.¹

• Treat underlying cause.
• Patients with chronic cough should avoid exposure to irritants that can trigger cough.⁴
• Smoking cessation.
• Referral to secondary care for opinion, investigation and management may be required and may require chest physician, ENT specialist, gastroenterologist or paediatrician, depending on individual context.⁴

Antitussive medication³

• The cause of an increased cough reflex often remains at least partly unexplained and treatments against potential aggravating factors are not fully effective. Antitussive therapies are then required:
• Codeine is the most commonly prescribed opioid-derived antitussive agent. It mainly acts centrally in the brainstem, but might also inhibit peripheral activation of cough receptors. Codeine can cause constipation and can cause dependence; pholcodine has fewer side-effects.
• A non-narcotic antitussive, dextromethorphan, has been shown to have some effect on cough associated with upper respiratory tract infections and also has less potential for side effects than codeine.
• The use of morphine and diamorphine is restricted to severe distressing cough in malignant disease, in which cough is often associated with pain and distress.
• Demulcent cough preparations contain soothing substances, e.g. syrup or glycerol, and may be useful for patients who have a productive cough.