Botox is the most effective and the safest preventive treatment for migraine headaches. However, in a very small number of patients, Botox loses its effectiveness over time. This happens for two main reasons – the person develops antibodies as a defense mechanism to block the effect of Botox or headaches change in character and stop responding to Botox.
It is easy to tell these two reasons apart. If Botox fails to stop movement of the forehead muscles and the patient can frown and raise her eyebrows, it is most likely because of antibodies. On a very rare occasion this is due to a defective vial of Botox, so to confirm that antibodies have formed, we give a small test dose amount of Botox into the forehead. If again there is no paralysis, we know that antibodies have developed. This can happen after one or two treatments or after 10, but in my experience over the past 25 years, significantly fewer than 1% of patients develop this problem.
Fortunately, some patients who develop antibodies to Botox, known as type A toxin, may respond to a similar product Myobloc, which is a type B toxin. Myobloc is not approved by the FDA to treat chronic migraine headaches, but it has a similar mechanism of action and has been shown to relieve migraines in several studies. Injections of Myobloc can be a little more painful, it begins to work a little faster than Botox, but the effect may last for a slightly shorter period of time.
An even smaller number of patients have naturally occurring antibodies to Botox, which is most likely due to an exposure to botulinum toxin in food. I’ve encountered 4 or 5 such patients and a couple of them who did go on to try Myobloc, did not respond to it either.
When Botox stops working despite providing good muscle relaxing effect, it could be because the headaches have changed in character, severity or are being caused by a new problem. It could be due a sudden increase in stress level, lack of sleep, hormonal changes, drop in magnesium level due to a gastro-intestinal problem, or another new illness, such as thyroid disease, diabetes, multiple sclerosis, or increased pressure in the brain. Such patients need to be re-evaluated with a neurological examination, blood tests, and usually an MRI scan. One of my patients who was doing well on Botox for several years, did not have any relief from her last regular treatment. Since she had no obvious reasons why her migraines should stop responding to Botox, I ordered an MRI scan. Unfortunately, she turned out to have brain metastases from breast cancer which had not yet been diagnosed.
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