Hi there I've posted before. i'm 27 (7 years later after asthma diagnosis), and after having some vocal cord issues from the inhaled cortisteroids, I was lowered to just flovent 250 twice a day. After being on it for about 2-3 months and after a normal PFT they had me do a metacholine challenge with no response. They are saying I can't have asthma because of the negative metacholine challenge. Is this true? What else could I have and what tests can I get to confirm?
The answer to your question depends, to some degree, on what is meant by “no response” to methacholine. Methacholine inhalation challenge is a valid, sensitive test (sensitivity 85%-90%) for diagnosing asthma, including occupational asthma, cough variant asthma, and exercise-induced asthma. The lower the concentration of this substance to cause a 20% fall in a specific pulmonary function test (FEV1), the more likely a positive test. Very low levels that result in a 20% fall, are positive.
The higher the concentration of Methacholine required to cause a fall of 20%, the more likely a negative test; always a negative test when the highest, safely deliverable concentration of methacholine, fails to cause any fall in the FEV! Very high levels that fail to cause a 0-20% fall are negative and in-between, there is a gray area on the test scale where the result may or may not be “positive”. Let’s assume that “no response” equals negative.
And the question is: is this negative challenge valid? Was the test performed valid, consistent with national standards. Is it falsely negative? Or is the diagnosis of asthma incorrect?
If the methacholine challenge were performed shortly after discontinuation of the Flovent, residual beneficial effects of the drug could result in a negative challenge. The beneficial effects of Flovent may persist for days to weeks after discontinuation of the drug, resulting in a negative challenge.
A number of diseases can mimic asthma and result in a negative challenge. An example is a disease called, Eosinophilic Bronchitis which is similar to asthma in clinical presentation (especially cough variant asthma) and responds favorably to inhaled corticosteroids. It is not usually associated with variable airflow obstruction, but wheezing can occur. It is likely that some of the “false-negative” methacholine tests represent eosinophilic bronchitis.
The best advice I can give is for you to seek consultation with a specialist with expertise in the diagnosis of asthma and in the interpretation of positive and negative methacholine challenges. Such specialists are Board Certified Allergists or Pulmonologists. They can speak to your question and provide more specific information about the preceding (above) and more, and how it applies specifically to you and your circumstance.
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