What diagnoses should you consider in a patient with a chronic cough and a normal chest X-ray?

That's a nice question. I think the best place to start is to try to remember the common causes of a chronic cough, which is defined as a cough lasting more than three weeks.

Briefly, if the patient is a smoker, always think of:

• Chronic obstructive pulmonary disease (COPD)
• Lung cancer

On the other hand, if the patient isn't a smoker, think mainly of:

• Postnasal drip syndrome
• Asthma
• Gastroesophageal reflux

And for either category, remember to ask the patient whether or not they're using an angiotensin-converting enzyme (ACE) inhibitor (e.g. for hypertension, cardiac failure or diabetes). This is a also a common cause of a chronic cough.

Of these, the 'non-smoker' three, plus the ACE inhibitor one, are the commonest causes of a chronic cough with a normal chest X-ray. The 'smoker' two are more likely to give you an abnormal X-ray, but in their earliest stages, their changes might not be apparent radiologically.

As I said, I'm deliberately only concentrating on the commonest causes. If none of these seem to fit, I'd ask for expert (i.e. pulmonologist) assistance. But that's just me...