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How is Cough Variant Asthma Diagnosed

Asthma incidence is on the rise with an estimated 4.1 million British adults already affected. Cough variant asthma is a particular type of asthma characterised by a non productive cough and no other common asthma symptoms. Indeed the absence of wheezing and shortness of breath make this type of asthma extremely hard to diagnose as the persistent cough is often put down to recurring chest infections or bronchitis. Exercise and exposure to dust, pollen or cold air are thought to bring on this type of asthma and the more I read about it the more I am convinced I am a sufferer of it. Quite frequently after I exercise or whilst I am on a brisk walk I get an unpleasant dry cough. Additionally I am allergic to dust mites and these too send me into coughing fits.

Spirometry is a common test used to diagnose asthma as it checks lung performance by measuring the amount of air given out by the lungs after inhaling deeply. In most asthma cases the test shows a reduced amount of exhaled air by the lungs indicating airway obstruction, but commonly in cough variant asthma the test gives a normal result thus not aiding diagnosis.

However a method that is particularly useful for diagnosing cough variant asthma is a metacholine challenge test which must performed under close supervision as it interferes with the airways causing them to shrink making breathing more difficult. During the specialised procedure the patient is required to inhale metacholine in an aerosol form pre and post spirometry. If the patient’s lung function drops by a fifth this suggests a positive metacholine test and a diagnosis of cough variant asthma. On finishing the test the patient must be given a drug to combat the effects of metacholine and help them open their airways again. The test can be particularly frightening for the patient as they will feel as if they are having a full blown asthma attack due to decreased exhaled air by the lungs. I would suggest that anyone going to have this test should have a discussion about the procedure before they undergo it.

A much simpler way but perhaps less effective and more time consuming way is to treat the patient with a selection of bronchodilators to open up the airways. If the patient responds to these drugs then this suggests a diagnosis of cough variant asthma. Personally I would rather have the metacholine challenge test for a much quicker diagnosis. The quicker you are diagnosed the quicker you can be treated and have your symptoms resolved. However you should expect at least 6 weeks before treatment with an inhaler starts to work.