Botulinum toxin type A is a neurotoxin produced by strains of the Clostridium botulinum bacteria that has therapeutic properties when injected into muscle tissue. Commercially known as Botox or Dysport, botulinum toxin A is most commonly known for its cosmetic applications, though it was initially used to treat spasticity and dystonia - i.e. strabismus (eye misalignment), blepharospasm (involuntary eyelid contraction), hemifacial spasm, cervical dystonia and focal dystonia. In more recent years, Botox has found clinical applications in the realm of pain management.
It is well known that Botox works to treat muscle spasms by inhibiting the release of acetylcholine at the nerve terminal within the muscle. This inhibition reduces muscular tone and overactivity - essentially relaxing the muscle. Botox is therefore effective in painful muscular conditions resulting from muscular spasms, contraction or overactivity, such as myofascial trigger points and some cases of myofascial pain syndrome.
Whilst there have been very few studies on the effectiveness of Botox in low back pain, a role for this treatment has been suggested for chronic low back pain of muscular origin, particularly when due to overactivity or stretch of the deep paravertebral muscles. One small study has shown promising results, however, large, controlled clinical trials are needed in order to supply stronger support for this clinical application.
Besides providing pain relief via its muscle relaxation effects, numerous studies have shown or suggest that Botox may also inhibit the release of several other neurotransmitters and/or interrupt other peripheral and central nervous system pathways involved in pain perception and signalling. A recent study has also provided insight into a role for Botox in activation of the endogenous opioid system. These actions may underlie the effectiveness of Botox in relieving inflammatory pain and neuropathic pain.
Preliminary data from small or pilot studies has provided support for effective pain relief with Botox treatment in complex regional pain syndrome, postherpetic neuralgia (pain following a shingles outbreak), brachial plexopathy (pain/dysfunction in the shoulder/arm usually due to nerve injury) and spinal cord injury. Recently, a randomised, double-blind, placebo-controlled trial has provided strong evidence for the effectiveness of Botox in the treatment of peripheral neuropathic pain of various causes, particularly in the reduction of allodynia.
Botox has also been shown to reduce sensory activity in the facial muscles arising from the cranial nerve and inhibit sensitisation in the face produced by the trigeminal nerve. These mechanisms are thought to underlie the potential effectiveness of Botox injections in relieving or preventing migraine/headache. Numerous studies have been conducted in patients suffering from migraine as well as chronic headaches, tension headaches and other headache syndromes that have shown positive results, however, large, controlled clinical trials are still warranted.
The injection procedure is simple and quick – approximately 15 minutes. The patient may have to cease some medications prior to the procedure. Prior to injection, the painful area(s) will be palpated and marked with a pen. The area(s) will then be cleaned with a chlorhexidine solution or alcohol wipe. Both Botox and local anaesthetic will be injected. It is recommended that the patient organises a lift home and rests for 24 hours after the injection. The local anaesthetic will wear off in roughly 12-18 hours and the Botox should take effect approximately 5 days post-injection. The benefits typically last for 3 months. Repeat injections are required to maintain long term relief.
Side effects are generally non-serious and there is no evidence for serious long term effects with repeated injections. Common side effects include initial discomfort at the injection site, temporary exacerbation of pain, muscle weakness, headache and flu-like symptoms.
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