Study suggests Botox can prolong the benefit of a nerve block for CRPS

The results of an interesting study have been published suggesting that Botox prolongs the benefit of lumbar sympathetic blocks in patients with Complex Regional Pain Syndrome (CRPS). Before considering the study further, let’s explore the role of both sympathetic nerve blocks and Botox in pain medicine.

What are sympathetic nerve blocks?

Sympathetic nerve blocks are a routine weapon in the pain medicine arsenal. They involve the injection of local anaesthetic and very often another drug to prolong its beneficial but short term effect.

For people suffering CRPS, the site for the injection will depend on where the CRPS has developed; the sympathetic nerves in the lower back (a lumbar sympathetic block) for the lower limb or the sympathetic nerves of the neck (a stellate ganglion block) for the upper. The procedure is performed under x-ray or ultrasound guidance to ensure the drug(s) is delivered to precisely the right spot.

In both cases, the target for the block is the sympathetic nervous system (SNS), which encompasses a whole series of nerves that radiate from the spine to control a host of involuntary functions, for example, sweating and blood flow. It’s believed that dysfunction of the SNS following trauma may play a significant role in developing and maintaining CRPS.

It must be stressed, however, that there is no guarantee that a nerve block will produce any benefit at all.

Botox for chronic pain

Botulinum Toxin (or Botox) is a purified protein produced from the highly potent and infectious toxin, Clostridium Botulinum. This is the same toxin that causes botulism, a potentially fatal form of food poisoning. But there are numerous varieties of Botox, each producing a different action on the body. The variety used in pain medicine is a temporary muscle-relaxant. It works by binding to the junction between nerves and muscles, blocking nerves that cause muscle contraction, reducing muscular hyperactivity and easing pain.

Botox is no newcomer to the treatment of chronic pain. In addition to CRPS, it’s been used for many years to treat conditions as diverse as neuropathic pain, myofascial pain syndrome (MPS), arthritis, chronic pelvic pain (CPP), chronic spinal pain, migraine and headache. Typically, it takes between two and four weeks before optimum relief is obtained. Although the beneficial effect is only temporary – usually lasting two or three months – occasionally the benefit lasts much longer.

The study

Now, researchers at Seoul National University Hospital in South Korea seem to have proved the hypothesis “that botulinum toxin would prolong the duration of a lumbar sympathetic block” in patients with CRPS in a lower limb.

Forty eight patients were randomly assigned to one of two groups; one group receiving Botox, the other (the control group), a local anaesthetic. As an objective measure, the researchers recorded the temperature of both soles on the patient’s feet before the block was administered, and again at intervals of one and three months. Also, using a visual analogue scale (VAS), they recorded reported pain intensity. On a VAS, a patient is asked to score their pain between zero and ten, where zero is no pain at all, and ten is the worst pain imaginable.

After one month, on average the Botox group recorded a higher temperature increase in the blocked foot than the control group, and this finding was maintained at three months. Crucially, however, the reduction in reported pain intensity was even greater than the temperature increase among the Botox group at both one and three months, with that reduction in pain lasting longer.