Botox® (onabotulinum toxin A) was licensed specifically for the treatment of chronic migraine in July 2010 by the Medicines and Healthcare products Regulatory Agency (MHRA).
Botox® has not as yet, been shown to be effective for any other headache type (e.g. episodic migraine, tension-type headache, cluster headache).
What is botulinum toxin?
Botulinum toxin in high doses causes Botulism, a paralysis of the muscles. It was first described in 1817. In 1895, Clostridium botulinum was isolated as the bacterium responsible.
Seven different subtypes of botulinum toxin (A-G) are known. A highly dilute preparation of botulinum toxin type A (Botox®) was introduced in clinical practice in the 1970s and 1980s to treat squint and blepharospasm. It has since then been used in other areas of medicine such as dystonia (including writer’s cramp), post-stroke spasticity, and hyperhidrosis. Other botulinum toxin preparations are available, both of type A (Dysport and Xeomin) and type B (Neurobloc or Myobloc), but these have never been tested in headache disorders.
Botulinum toxin and headache
In the mid-1990s a number of people reported improvement in headaches in patients receiving botulinum toxin for other reasons. Well-conducted clinical trials of botulinum toxin in various types of headache followed, but with generally disappointing results.
However on more detailed analysis the results did suggest that there might be a subgroup of patients with chronic migraine who could benefit, and the Two Phase 3 Research Evaluating Migraine Prophylaxis Therapy (PREEMPT) trials followed.
These trials recruited 1384 patients with chronic migraine, randomised to treatment with Botox® or placebo. These patients were suffering on average 20 days of headache each month, of which 18 were moderate or severe. Those randomised to Botox® received fixed-site, fixed dose injections every 12 weeks over 56 weeks. These injections covered seven specific areas of the head and neck, with a total dose of between 155-195 units.
At six months, after two cycles of treatment, those treated with Botox® had on average eight less days of headache each month. After 12 months, 70% of those treated had ≤50% the number of headaches that they had done originally. Botox® was well-tolerated, the commonest side effects being neck pain (6.7%), muscular weakness (5.5%), and drooping of the eyelid (3.3%). No serious irreversible side effects have ever been reported in trials of Botox® in headache.
How does botulinum toxin work in chronic migraine?
We don’t as yet know exactly how it works. It does not appear to work by relaxing overactivemuscles as it does in other conditions. It is believed to inhibit the release of peripheral nociceptive neurotransmitters, which may then have a knock-on effect on the central pain processing systems that generate migraine headaches.
Is Botox® right for me?
It is essential you discuss your options and suitability for treatment with a medical practitioner experienced in the diagnosis and management of headaches before making your informed decision. Be aware, rules differ in Scotland.