Annie,
I briefly went over your link.
This was clearly written by someone who has no understanding of MG.
The following sentence shows where many errors in understanding PFTs of MG patients come from-
Quote:
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. A recent study has shown start-of-test problems (affecting FEV1 measurements) to be relatively uncommon (2% prevalence in one series) and end-of-test problems (affecting FVC quality) being very common (61-84% prevalence). Allowing the patient to relax and push gently after 3-4 seconds of forced exhalation has been shown to greatly enhance the ability of patients with airflow obstruction to satisfy end-of-test criteria.
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So, you have a patient in which the VC significantly drops after a few efforts. what do you do? you let the patient rest, and then repeat it again.
This is exactly how you are going to miss significant respiratory muscle involvement of myasthenia!
Further more, even in patients with lung diseases or asthma, there are studies that show an element of respiratory muscle involvement, so their low results may also be real, and explain why it is so common.
In medicine, you can't carve order by leaving the disorderly parts out. This is a fertile source for serious clinical errors.