Predicting response to Botox in chronic migraine.

Botox is a very effective treatment for chronic migraines and possibly other types of headaches and pain. However, Botox is an expensive and somewhat unpleasant treatment. Even though Botox helps a high percentage of patients (about 70%) it would be useful if we could predict who is going to respond and who is not.

One of the predictors seems to be the directionality of pain. That is, if patients with migraine who have constricting (imploding) pain or pain localized to the eye seem to respond better than those who have pain that seems to be pushing from inside out (exploding). This is not a very reliable predictor because some people have difficulty categorizing their pain in that way and because even if they do describe it clearly one way or another, this predictor is far from 100% accurate.

In a study just published in the journal Headache a group of Spanish neurologists claim that they have found a predictor with 95% accuracy. They measured blood levels of calcitonin gene-related peptide (CGRP) and found that those with levels of CGRP above a certain number were 28 times more likely to respond to Botox than those with levels below that level.

CGRP has been shown to be very involved in the process of migraine and several drugs and antibodies which block the CGRP receptor appear to be very promising (see my recent blog post on such antibodies). So, it is not very surprising that this correlation between the response to Botox and blood level of CGRP was found. However, this finding needs to be confirmed in a larger group of patients (this study involved 81 patients) and this test needs to become available commercially since now it can be done only in research laboratories.