Comment gérer la douleur chronique

We all know what it's like to be in pain but thankfully, for most of us, that pain is temporary and easily treatable. Known as nociceptive pain, the sensation is the body's acute response to inflammation and tissue damage - due to bumps, burns, sprains or broken bones - and usually resolves as a result of our natural healing process.

Chronic pain is very different. It persists beyond the normal period of time expected for healing and is often resistant to treatment. Symptoms may be related to medical conditions such as diabète, l'arthrite et le cancer, or as a complication of previous injury or surgery that can sometimes manifest as syndrome douloureux régional complexe. Another major cause of chronic pain is neuropathy, which affects up to 10% of the general population.

It is estimated that 14 million people live with chronic pain in England alone and severe unremitting pain impacts on every aspect of life, according to The Future for People with Chronic Pain, a recent policy document produced by the Faculty of Pain Medicine of the Royal College of Anaesthetists.

Douleur neuropathique

Neuropathy is a major cause of chronic pain and can result from diabetes, sclérose en plaques, spinal injury, the amputation of a limb and many other disorders. It also presents as pain conditions such as fibromyalgia et vulvodynie.

Dr Ivan Ramos-Galvez, a consultant in pain medicine at the London Pain Clinic explains:

"Neuropathic pain is there for no purpose. It's relentless and often felt as a terrible burning or prickly sensation. It occurs when the nerve endings that send signals about sensation to the brain fire continuously or at a much lower threshold than would normally be felt. This produces a higher release of chemical signal than is normal, which is read by the brain as pain."

The drugs commonly used to treat nociceptive pain, such as paracetamol and ibuprofen, aren’t effective for neuropathy.

"That's because primarily they reduce inflammation and that's not what neuropathic pain is," says Ramos-Galvez. "Neuropathy needs to be treated with drugs designed to change chemical pathways in the brain and the central nervous system."

Antidepressants and anti-seizure medications

Antidépresseurs tricycliques and drugs that were originally designed to treat épilepsie can be useful in treating neuropathic pain because they reduce overactivity of the central nervous system.

"Oral medications gabapentine et prégabaline, which are anti-seizure drugs, work on the calcium channels that reduce nerve signalling, and tricyclic drugs such as amitriptyline et nortriptyline also work on the link between the nerve cells," says Ramos-Galvez.

These drugs offer effective pain relief, but it can take time to build up the dosage to the optimum level. Side effects include cognitive impairment, tiredness and, with anti-epilepsy drugs, weight gain.

Duloxétine, a relatively new antidepressant medication, has been shown to reduce the painful symptoms of fibromyalgia. It works differently to tricyclic antidepressants, calming down pain signals by increasing the level of two naturally occurring substances - serotonin and norepinephrine.

Topical medications

For localised neuropathic pain, use of local anaesthetics (including lidocaine plasters) and capsaicin cream, which is derived from chilli peppers, may be appropriate.

"Also, gabapentin and ketamine can be combined in creams that can be helpful for specific types of neuropathic pain," says Ramos-Galvez, "but they have a very superficial effect on the nerves in the skin so although they might reduce sensitivity and change the sensation, they may not take the pain away completely."

These creams may help with conditions such as diabetic neuropathy and vulvodynia and, more recently, studies using phenytoin cream have been successful. However, these topical preparations are not widely available on NHS prescription.

Standard interventions for chronic pain include drug therapies, anaesthetic injections, surgery and other techniques to try to reduce symptoms.

Opioïdes

The synthetic opioid drugs morphine, codéine et oxycodone work on opioid receptors in the central nervous system. They provide fast-acting, effective pain relief, but long-term use can cause tolerance, meaning higher doses are required to achieve the same effect, and the drugs can induce a euphoric 'high' that may lead to addiction.

The use of opioids needs to be managed by a specialist pain physician, as careless prescribing has resulted in a major 'opioid crisis' worldwide.

"There was a felt pressure to provide pain relief for large numbers of people who were clearly suffering," explains Ramos-Galvez, "but poor supervision of the prescribing of these drugs meant they were used for the wrong reasons and in unnecessarily high doses for too long a time."

Neuromodulation

This technology is proving successful in altering nerve activity by delivering electrical or pharmaceutical drugs directly to the brain, spinal cord or other target areas; a low-voltage electrical current passes from a powered generator to the nerve which can inhibit pain signals.

Mindfulness and psychological therapies

Therapies such as la pleine conscience, meditation, la thérapie cognitivo-comportementale and eye movement desensitisation and reprocessing (EMDR) have been shown to reduce the perception of pain in some patients and improve quality of life.

"The pain might still remain, but what these therapies can do is improve sleep and reduce the frustration and stress that may make pain feel worse," says Ramos-Galvez.

A number of des études have shown that mindfulness and meditation practices can markedly reduce pain symptoms.

"It's interesting that in MRI scans of Buddhist monks and long-term meditators, the areas of the brain related to pain still light up when stimulated, but the areas related to the response to the pain don't," adds Ramos-Galvez. "So people who meditate still feel the same sensation of pain, but the brain doesn't activate a response, so effectively it reduces the distressing effect."

The brain switches to accepting and ignoring discomfort rather than fighting it or running away from it, which are the two standard human responses to pain which increase stress.

With so many people suffering from chronic pain, it's no wonder that researchers are investigating ways to relieve and manage it. Thankfully, there has been some recent progress worth celebrating.

New opioid drugs

Tapentadol is a relatively new drug that has garnered interest from pain clinicians as it has been marketed as an opioid subtype with a lower risk of addiction.

"This is because it does not appear to work on the 'reward pathway' in the brain that other common opioids activate, so there is less risk of an addiction developing," explains Ramos-Galvez.

Cannabinoids

The active constituents of the drug cannabis have been a talking point in recent months but, as yet, are only available on NHS prescription for extremely limited indications. Cannabinoids include cannabidiol (CBD) and tetrahydrocannabinol (THC), two natural compounds found in cannabis plants, but THC in particular should be used with caution, according to Ramos-Galvez.

"It's about getting the balance right of CBD and THC," he says. "You need enough THC to induce pain relief, but too much without adding in an optimal amount of CBD has been shown to cause psychiatric symptoms such as paranoia."

There are several manufactured forms of combined CBD and THC available for clinical use, but these are bound by government restrictions. Prescribing of cannabis-based products officially became legal in the UK in late 2018, but only a handful of prescriptions was issued in the first few months and many pressure groups complained the regulations were too restrictive.

In November 2019, the National Institute for Health and Care Excellence (NICE) issued guidance on cannabis-based medical products, but these only recommend them as an option for spasticity in multiple sclerosis and certain forms of severe, treatment-resistant epilepsy. Importantly, although one CBD/THC-containing drug, Sativex, has shown benefit and is licensed in some countries for treating neuropathic pain, the NICE guidance did not recommend it for any form of pain treatment.

"It's not something that I would prescribe as the first line of treatment," adds Ramos-Galvez, "as we don't really know what the long-term effects are. More trials are needed, but the current research is promising."

If you're living with persistent pain, your GP can advise and may suggest further tests are carried out, or that you see a relevant medical specialist to establish the cause.

Chronic pain that doesn't respond to standard treatments may be better managed by a consultant in pain medicine at a specialist pain clinic. For support and information on living with pain, contact Pain Concern and the British Pain Society.