David Yeomans, PhD, associate professor of anesthesiology, perioperative, and pain medicine at Stanford University School of Medicine, discusses the challenges of evaluating pain associated with migraine.
Secondary symptoms like nausea also need to be taken into account when evaluting migraine treatment efficacy, said David Yeomans, PhD, associate professor of anesthesiology, perioperative, and pain medicine at Stanford University School of Medicine.
Because pain is subjective, can you elaborate on some of the challenges of studying migraine?
It's a fairly standard way that companies, for example, will do that, that the FDA has accepted that methodology. But you're right, the pain is clearly subjective. But what you do is you look at pain, you've probably heard of the 0 to 10 scale. You go to the doctor, they say how much pain, "Oh it's a 6." With migraine, they use a different scale. It's a 4-point scale, where you say, severe, moderate, mild or none. And it's a little easier for people to categorize. And so there's that. What you're looking for is a decrease from severe or moderate down to mild or none. That's considered a positive response.
But you also have to look at the secondary symptoms. So, what's called the most bothersome secondary symptoms, like nausea, or photophobia, or phonophobia. So whatever is the most bothersome to a patient. You look at not only the pain level, but how much your treatment is affecting this secondary thing.
There's also some biomarkers that people are investigating. For example, we know when these trigeminal neurons are active, they release something called CGRP, calcitonin gene-related peptide. It's a neurotransmitter. That's the target for some of these newer drugs that have come out, either CGRP antibodies or CGRP antagonists to block CGRP. Turns out, you can measure CGRP either in the blood or the saliva. It looks like when CGRP is elevated, that's a clear strong correlation to how much pain you have. It's not established yet, that is to say, the FDA doesn't accept it yet. But it looks like that should be a decent biochemical marker of how active these pain neurons in the trigeminal neuron are. Pain is not in the peripheral nerves, pain is up here in the cortex in the brain. There's a lot of steps in between. But for something like this, just measuring CGRP seems like it's a pretty good indicator of how much pain a person's having.