Trial by Inhaler - Bronchiolitis vs Viral Wheeze

With wheeze in children becoming a major presentation again, it feels like a good time to explore the issue of deciding whether a child has bronchiolitis or viral induced wheeze.  There are various way that people do this in practice.  Many stick to a strict 12 month cut off.  This method works reasonably well and is rarely problematic.  Bronchospasm is rare below this age and if it is going to be problematic under the age of 12 months, in my experience the infant is severely distressed and gets bronchodilators out of desperation rather than a diagnostic trial.

I have already explored a method of determining whether the pathology causing wheeze is predominantly wetness (bronchiolitis) or tightness (viral induced wheeze/ bronchospasm) by using age combined with the story.

Slow accumulation of moisture and mucous tends to cause worsening of symptoms over days whereas bronchospasm causes acute change over hours.  My opinion is that in the majority of cases, the age and the story will correlate.

Where the patient is in the overlap zone (e.g. 10-15 months old) and the story is clear (e.g. snotty/ coughing on Monday, struggling with feeds on Tuesday, noisy breathing on Wednesday and fast breathing on Thursday) then the story gives the diagnosis.  With age/ story correlation or where the age allows ambiguity but the story is clear, the diagnosis is made.

So what about simply trying an inhaler to see if it works?  This alternative approach to the age of overlap sounds straightforward and is reasonably common in practice, but is it logical?

A therapeutic trial works best when a clinical effect is guaranteed and unambiguous.  Neither of these things is true in this situation.  With viral wheeze, which should respond to salbutamol, clinically apparent response may require increased or repeated doses.  Bronchiolitis, which will not respond, is famous for mini-fluctuations in work of breathing.  This is caused by mucous plugging or the clearing of secretions.

When you think of it in these terms, trying an inhaler doesn't meet the quality standards required of a valid test.

Trial by inhaler is also problematic due to human bias.  Uncertainty is fertile ground for biases to mislead us when an inhaler is given to make a diagnosis rather than as treatment.  It is better to use beta-agonists therapeutically where appropriate and to see non-response as a reason to reconsider a presumed diagnosis of viral wheeze.  If viral wheeze is the problem, we should not allow the lack of effect to refute the diagnosis.

Edward Snelson

@sailordoctor

Disclaimer - when I wrote this, I briefly thought that you could bring logic to medicine.  I know, right?!?