Cough is a reflex explosive expiration that prevents aspiration and promotes the removal of secretions and foreign particles from the lung.
Differential Diagnosis of Cough:
Major causes of cough are divided into two broad categories i.e Acute and Chronic. Chronic cough is sometimes again divided into productive and non productive cough.
Following are the main causes of cough, we can reach our diagnosis by pertinent history, examination and investigations if required.
Onset and duration:
The onset of a cough may be acute or chronic (usually defined as a
cough that has persisted for more than three weeks). Sudden onset
of an unrelenting bout of violent coughing may be due to an inhaled
foreign body. If this is large enough to occlude the airway, coughing
abruptly ceases and is supervened by cyanosis and eventually
The frequency, quantity and appearance of expectorated sputum
can be very helpful in the differential diagnosis. Cough 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 TB.
Smoking alone may cause a chronic cough; however, a long
smoking history predisposes to bronchogenic carcinoma and chronic
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 TB.
Pleuritic chest pain may be experienced with pulmonary emboli
and pneumonia; unrelenting chest pain is more suggestive of
bony metastasis from lung cancer. Retrosternal burning chest pain
precipitated by posture suggests gastro-oesophageal reflux disease,
and the associated cough is due to aspiration of refluxed material.
Frequent clearing of the throat due to nasal discharge or a history
of allergy with rhinitis may result in post-nasal drip and precipitate
The presence of pyrexia usually indicates an infective aetiology; the
temperature may also be raised with pulmonary embolism.
Inspection and palpation:
With COPD, the chest may be barrel-shaped. Patients suffering with
lung cancer or TB may appear cachectic. Cyanosis is a feature of
pulmonary embolism and COPD. The fingers should be inspected
for clubbing, which is associated with bronchial carcinoma
and bronchiectasis. The JVP is raised in congestive cardiac failure.
The supraclavicular nodes may be palpable with respiratory tract
infections, TB and lung cancer.
On auscultation, coarse crepitations are a feature of bronchiectasis
and pulmonary oedema. Auscultatory features of bronchial
carcinoma are non-specific and may manifest as a pleural effusion
(dull to percussion, absent breath sounds, decreased vocal resonance)
or segmental collapse of the lung. Widespread wheezing is
suggestive of asthma, and a fixed inspiratory wheeze may be heard
with bronchial luminal obstruction.
General investigations should be followed by specific investigations
if required to confirm the diagnosis. General investigations include:
If a productive cough is present, sputum should be sent for
cultures. This will include TB-specific cultures and Ziehl–Neelsen
Bedside determination of peak expiratory flow rate is useful in
the diagnosis of asthma (low peak flow).
White cell Count
A raised WCC is a non-specific indicator of infection, as it may
also be raised with pulmonary embolism.
Very useful and may reveal areas of consolidation with
infection. Dilated bronchi with persistent areas of infection are
suggestive of bronchiectasis. Apical pulmonary consolidation
with calcification and hilar lymphadenopathy is characteristic
of TB. The presence of pulmonary oedema is appreciated by
bilateral patchy shadowing; this may be accompanied by other
radiological features of cardiac failure, including cardiomegaly,
upper lobe diversion of the pulmonary veins, bilateral
pleural effusions and Kerley B lines (1–2 cm horizontal lines
in the periphery of the lung fields). Bronchial carcinoma may
present as a hilar mass, peripheral mass or with collapse and
consolidation of the lung due to airway obstruction. Bilateral
hilar lymphadenopathy is suggestive of sarcoidosis.
Respiratory function tests
Formal respiratory function tests can be used to diagnose airway
obstruction (asthma, chronic bronchitis and bronchiectasis) and
flow volume loops may reveal fixed airway obstruction.
Some useful specific investigations include:
Indicated when the diagnosis of pulmonary embolism is
suspected (especially where CXR is normal).
May be indicated in severely ill patients with suspected
pulmonary embolism when surgery or thrombolysis is being
Useful for the diagnosis and staging of lung cancer; it is also
specific for the diagnosis of bronchiectasis.
24-hour pH monitoring may be required when a diagnosis
of gastro-oesophageal reflux disease cannot be made on the
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