Introduction – Botulinum toxin (Botox®) for chronic migraine
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 been shown to be effective for any other headache type (e.g. tension-type headache, cluster headache) as yet. This fact sheet outlines the evidence for the use of botulinum toxin in headache.
What is botulinum toxin?
Botulism – paralysis of muscles caused by high doses of botulinum toxin – was first described in 1817. The responsible bacterium is Clostridium botulinum. 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 1970/80’s to treat squint and blepharospasm(eye twitch). Since then it has found uses in other areas of medicine including dystonia (including writer’s cramp), post-stroke spasticity, and hyperhidrosis (excess sweating). 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-1990’s 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 the results were disappointing, with no difference over placebo being found in tension-type headache, episodic migraine, and undifferentiated chronic headache. Detailed analysis of the results suggested, however, that there might be a subgroup of patients with chronic migraine who could benefit, and further trials were undertaken.
Botox® in chronic migraine: the PREEMPT trials
The PREEMPT trials recruited 1384 patients with chronic migraine, and randomised them 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?
The simple answer is that we don’t know – yet. Unlike many of the other conditions in which it is used, it is not thought to work by relaxing overactive muscles.
Botulinum toxin has been shown to reduce pain in a number of disease states, including cervical dystonia, neuropathic pain, lower back pain, spasticity, myofascial pain, and bladder pain. Botulinum toxin is believed to inhibit the release neurotransmitters, which may then have a knock-on effect on the central pain processing systems that generate migraine headaches.
Is Botox® right for me?
Only patients with chronic migraine are eligible for treatment with Botox®. Chronic migraine is defined as headaches occurring on 15 or more days each month, at least half of which have migrainous features.
There are, however, other treatments available to patients with chronic migraine, and it is important that patients have an informed discussion of their headaches and the options for treatment with a practitioner experienced in the diagnosis and management of headaches before a decision to use Botox® is taken.