Botulinum toxin and Migraine
Botulinum toxin (onabotulinum toxin A) was licensed specifically for the treatment of chronic migraine in July 2010 by the Irish Medicines Board and the UK Medicines and Healthcare products Regulatory Agency (MHRA).
What is botulinum toxin?
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. 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 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
Two Phase 3 Research Evaluating Migraine Prophylaxis Therapy (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. 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 fully. A recent US study by Rami Burstein et al using animal models suggested that botulinum toxin inhibits pain in chronic migraine by reducing the expression of certain pain pathways involving nerve cells in the trigeminovascular system. The trigeminovascular system is a sensory pathway thought to play a key role in the headache phase of a migraine attack.
Is Botox® right for me?
Only patients with chronic migraine are eligible for treatment with Botulinum toxin. 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.
Who can inject Botox® for chronic migraine?
At present, the use of Botox® is restricted to a few specialist headache centres, but as time goes on there should be increasing numbers of trained injectors available. In all cases, however, you should ensure that the person injecting has received appropriate training, both in the diagnosis and management of chronic migraine.
Dr Treacy has a long experience with Botulinum toxin and Migraine and has lectured on this subject since 2003.