Famous for wrinkle reduction, Botox is less well known for its treatment of chronic pain. Claire O'Connell reports on the toxin that has it all.
Botox is the darling of Hollywood, where it plays a starring role as an anti-wrinkle treatment.
Beloved of celebrities and lesser mortals alike, it is the leading non-surgical cosmetic procedure in the US, with an estimated three million treatments in 2004.
But Botox is more than just a pretty face. A muscle relaxant, the drug can help manage symptoms of neuromuscular disorders such as cerebral palsy, and it is emerging as a treatment for chronic pain.
Botox is a trade name for botulinum toxin A, a protein that disrupts nerve-muscle communication. Produced by spores of the bacterium, Clostridium botulinum, the toxin is the active agent in botulism, a potentially fatal illness.
Ironically, the potent toxicity of this nerve blocker is what has made it such a successful medical therapy.
Purified botulinum toxin was approved to treat crossed eyes (strabismus) and uncontrolled blinking in the 1980s.
Since then it has become a well-established local treatment for controlling involuntary muscle spasms in a range of neurological conditions including cerebral palsy, multiple sclerosis and Parkinson's disease. Recently, doctors have also used Botox to relax bladder muscles in patients suffering from overactive bladder conditions.
A series of chance observations have led to the toxin being used for more than the medical control of muscle contraction.
Initially, patients undergoing Botox therapy for eye conditions noticed fewer wrinkles around the paralysed area. This prompted dermatologists to start using the drug as a cosmetic treatment.
Then some patients receiving Botox for facial wrinkles reported a reduction in the severity of tension headaches and migraines, leading neurologists to investigate botulinum toxin as a pain-reliever.
Researchers are currently figuring out how the drug works as an analgesic.
Where pain is caused by muscle spasms or tension, it provides relief by relaxing the affected muscles.
Initial studies on migraine and other chronic pain conditions suggest that the toxin may also block the sensitisation of pain sensory neurons called nociceptors, which are involved in registering chronic pain.
But the story isn't clearcut. For example, Botox is not a primary treatment for migraine, a neurological condition that affects at least 400,000 people in Ireland, but for some patients the toxin can provide relief where other therapies have failed.
Results from a recent extensive clinical study in the US indicate the drug is associated with a 50 per cent reduction of chronic daily headache symptoms in migraine sufferers.
However, Peter Murphy, chief executive officer of the Migraine Association of Ireland, advises caution.
"It's a potential route forward, but research is ongoing and we would not recommend it at present. We await the outcome of further trials with interest," he says.
Results presented in Boston at the American Pain Society's annual conference in April also highlight the potential role for Botox in chronic pain relief.
Two studies indicated that botulinum toxin can relieve chronic pain when injected under the skin. A separate report echoed previous observations that the drug can alleviate chronic back pain. These studies are small scale, but they add to a growing body of data suggesting that botulinum toxin has direct pain-killing properties.
Dr Hugh Gallagher, a pain specialist and consultant anaesthetist at St Columcille and St Vincent's University Hospitals in Dublin, uses botulinum toxin in the management of chronic pain conditions such as fibromyalgia and myofascial pain, which affect muscles and soft tissue.
He explains the drug is part of a wider treatment regimen. For example, he might administer it as a muscle relaxant so a patient can gain more from physiotherapy or make lifestyle changes that will help control the condition.
"It's a means of facilitating rehabilitation of people with chronic pain," he says.
However, Dr Gallagher cautions that botulinum toxin is not a cure for all ills and that chronic pain is a complex area, which may have psychological as well as physical causes.
"It's not the first drug you'd reach for, but it has the potential to be used in a broader sense in many types of chronic pain problems. It's an area of growing interest.
"The local application of Botox avoids the blunderbuss effect of putting an oral drug into someone's system where you may get side-effects such as stomach problems, allergies or skin rashes," he says, noting that people are looking for more localised alternatives for pain relief.
Despite being a deadly poison, botulinum toxin has a good safety profile when used appropriately.
This bodes well for the drug's future in a safety-conscious market that has recently seen the withdrawal of the blockbuster systemic painkillers, Vioxx and Bextra, over concerns about side-effects.
The future role of Botox in chronic pain relief is one to watch.
The toxin science