Wednesday, April 29, 2009

Causes of cough and its diagnosis.

What is Cough?
Cough is a reflex explosive expiration that prevents aspiration and promotes the removal of secretions and foreign particles from the lung.

The onset of a cough may be acute or chronic (usually defined as a cough that has persisted for more than 3 weeks). Sudden onset of unrelenting violent coughing can be due to an inhaled foreign body.

Cough that is continuously productive of purulent sputum is suggestive of chronic bronchitis and bronchiectasis. Expectorated bloodstained sputum tends to be a complaint of patients with bronchogenic carcinoma, pulmonary embolism and tuberculosis.

Different causes of a cough

Acute
Inhaled foreign body
Respiratory tract infection
Pulmonary embolism (bloodstained sputum)

Chronic

Productive

Chronic obstructive pulmonary disease (mucoid/purulent)
Bronchiectasis (purulent)
Pulmonary oedema (pink, frothy)
Lung cancer (bloodstained)
TB (bloodstained)

Non-productive
Asthma
Postnasal drip
Gastro-oesophageal reflux
Drugs (ACE inhibitors)
Sarcoidosis



How to search the reasons for cough?

Smoking alone may cause a chronic cough; however, a long smoking history should alert the clinician to bronchogenic carcinoma and chronic bronchitis as underlying causes, especially if there is a change in the character of the cough.

Episodic (or even seasonal) wheezing with shortness of breath is common with asthma. This should be differentiated from the monophonic wheeze, which is suggestive of intraluminal obstruction from foreign bodies or tumour.

Most of the respiratory causes of coughing tend to be accompanied by shortness of breath, but sudden onset of dyspnoea may result from aspiration or pulmonary embolism. Shortness of breath that is worse on recumbency is suggestive of pulmonary oedema; however, asthma may also be worse at night. Weight loss can be a prominent feature with lung tumours and tuberculosis.

Associated pleuritic chest pain may be experienced with pulmonary emboli and pneumonia; unrelenting chest pain is more suggestive of bone involvement from lung cancer. Associated symptoms of gastro-oesophageal reflux disease may indicate aspiration of refluxed material. Frequent clearing of the throat due to nasal discharge or a history of allergy with rhinitis may result in postnasal drip and precipitate coughing.


The presence of pyrexia usually indicates an infective aetiology; the temperature may also be raised with pulmonary embolism.

The chest may be barrel-shaped with chronic obstructive pulmonary disease. These patients, as well as those with lung cancer or tuberculosis, may appear cachectic. Clubbing is associated with bronchial carcinoma, fibrotic lung disease and bronchiectasis. The supraclavicular nodes may be palpable with respiratory tract infections, tuberculosis and lung cancer.

On auscultation, coarse crepitations are a feature of bronchiectasis and pulmonary oedema. Widespread wheezing is suggestive of asthma, and a fixed inspiratory wheeze may be heard with bronchial luminal obstruction.

Investigations for cough

Investigations are not required for all patients that present with a cough, and should be reserved for patients in whom the underlying aetiology is not clear after initial clinical assessment, patients with suspected chest infections or if a serious underlying disorder is suspected.

Sputum cultures
If a productive cough is present, sputum should be sent for cultures in an attempt to isolate any bacterial cause. If tuberculosis is suspected, Ziehl-Neelsen staining and specific culture on Löwenstein-Jensen media is required.

Full blood count
A raised white cell count is a non-specific indicator of infection.

Chest X-ray
A chest film is most useful in patients in whom pneumonia, lung cancer or cardiac failure is suspected.

Respiratory function tests
Formal respiratory function tests are usually reserved for patients with suspected airway obstruction (asthma, chronic bronchitis and bronchiectasis).

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