Neurotransmitter levels in the brain. And reliably. (Some sort of panel of blood tests, I presume.) I don’t want someone who’d do, say, the urine-test method. How would THAT tell you anything about the levels in the brain?
On a fundamental level, you can divide MAV into two types: episodic and constant. We know there may be brain-chemical-levels abnormalities (esp. of serotonin) during migraine “attacks,” or episodes, but what about those who are dizzy all the time? Seems to me that if you have someone who’s constantly dizzy, you don’t have to catch them “during a migraine episode” (to test them) because their condition is always present!
I’m speculating that in “constant MAV,” one or more neurotransmitters are “malfunctioning” (i.e., some levels are too low, some are too high, etc) without interruption. The counterpart idea is that “episodic MAV” is similar, but that levels are fluctuating (spiking and dropping, but at normal levels for certain intervals of time).
Not unlike “a complete, extended blackout” versus “power surges and brownouts.”