Botulinum toxin is now licensed as a treatment for chronic migraine. Because migraine is so prevalent, many patients will be seeking this new treatment.
Since it was introduced into clinical practice, botulinum toxin has found a wide range of applications ranging from the treatment of spasticity to hyperhidrosis. Despite having failed to reach superiority over placebo in RCTs in chronic tension-type headache or episodic migraine, it is widely used for the treatment of many headache types in private practice, particularly in the US.
Recently, two RCTs in chronic migraine have shown statistically significant improvement over placebo, with some 20 per cent improvement over placebo in days free from headache.
What is chronic migraine?
In 1994 the term 'transformed migraine' was introduced. It was recognised that each year approximately four per cent of people with episodic migraine will transform to a more chronic problem, invariably associated with medication overuse.
More recently this term has been superseded by 'chronic migraine', a headache on 15 days of the month or more for greater than three months, of which eight days of headache are migraine. Approximately one per cent of the population suffers from chronic migraine.
Chronic migraine is often confused with chronic daily headache, a descriptive term which describes headache occurring on more than 15 days of the month.
Chronic daily headache is a misleading term and should be replaced by the diagnosis of the underlying condition. For example, chronic migraine, chronic tension-type headache, hemicrania continuum, or new persistent daily headache.
SPECT scan: low brain activity caused by migraine (green, lower left) (Photograph: SPL)
Causes of chronic migraine
A likely cause of chronic migraine is over-sensitivity of the mid-brain migraine generator, but the pathophysiology of chronic migraine is not fully understood.
Chronic migraine invariably sits within a complex biopsychosocial framework. Inevitably there is a steady progression of headache frequency, often complicated by medication overuse.
This leads to a self-perpetuating spiral of anxiety, depression and increasing frequency of headache.
Practical implications of botulinum toxin treatment
A number of injections in specified locations in the facial muscles are given. These need to be repeated every three months. It is not known how long the regular injections have to be continued as trial data is only available for one year.
The mode of action is not known although there is a suggestion that botulinum toxin may act on central sensitisation pathways. There is no cosmetic impact with the treatment protocol so patients cannot expect an extra bonus of cosmetic enhancement.
Initially, the treatment will be offered from a limited number of tertiary headache centres in the UK but inevitably there will be funding issues. Each treatment costs £270. Botulinum toxin will be offered more widely in private headache centres.
Patients with chronic migraine are often taking excessive analgesia and have developed a self-perpetuating spiral of migraine impact, causing exacerbation of psychosocial factors, leading to more frequent migraine.
Prednisolone (unlicensed indication) is useful to retain migraine control quickly and support cessation of analgesia overuse, which is an essential first step. There are no studies to support this intervention but prednisolone 1mg/kg up to 60mg a day for three days, then reducing over three weeks, is a reasonable approach.
Preventive medication is the cornerstone of treatment. Although all migraine preventers, for example beta-blockers or amitriptyline, would be acceptable, there is an evidence base to support topiramate. Amitriptyline is particularly useful if there is associated anxiety, depression or sleep problems.
There is likely to be considerable interest in botulinum toxin now it is licensed for chronic migraine. GPs should be aware that only a very small number of migraineurs will be eligible and that practical and funding issues may limit availability.
- Dr Kernick is a GP in Devon and RCGP headache champion