The association between the menstrual cycle and migraines has long been recognized, so much so that it has spawned its own diagnostic category.
--- Does "so much so" refer to the "recognized"? So this recognition brought about the creation of a new diagnostic category?
You are right to wonder. There is a weak connection. "So much so" seems to refer to the length of the recognition, not what is meant (as far as I can tell), and even that is a poor fit.
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You are right to wonder. There is a weak connection. "So much so" seems to refer to the length of the recognition, not what is meant (as far as I can tell), and even that is a poor fit. The writer seems to be trying to make his tenuous understanding of a debatable link into near fact by ineptly juggling words. If I was trying to sell you a quack migraine cure, I would write something more like
"So much so" means "to such an extent". Does that help answer your question.