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Phantom Limb Pain

March 18th, 2009 | Add a Comment

The brain’s sensory cortex, which receives and interprets incoming information, maintains a representation of the body physically within itself. The homunculus is the name given to the diagram obtained when each part of the body is plotted against its place on the sensory cortex, with more important areas of the body being illustrated as larger areas of the brain. Various areas, such as the hands and the lips, take up much more brain area due to their importance in normal function, and it is these most important areas to control which need greater sensory awareness and greater processing power to work out responses.

When we suffer an injury the pain comes directly from that part, streaming in from the highly irritated nerve ends and the normally silent nerves woken up by the chemical soup of the injury. As the barrage of impulses comes in to the spinal cord it meets the second stage nerves which will take the messages on into the central nervous system. These second stage nerves become highly excited by the incoming torrents of impulses and amplify the signal significantly, passing on much higher pain levels to the higher brain centres.

Pain needs to get through up to the brain and force its way into our conscious minds until we feel it, as our pains are always in our minds strictly speaking. Pain is never imaginary but our brains construct a virtual sensory reality so we can make sense of the world which includes touch, pain and visual realities. It is important to realise that the brain builds the pain experience that we endure and that this is not made up by our injured neck, disc prolapse or torn ligament.

When a limb in amputated it is obvious the muscles, ligaments and bones are all cut, but what is less clear, and much more important for the future, is that the nerves travelling down the part are also cut through. Cutting the part of the nervous system off from the centre means a sudden loss of incoming signals from the amputated part, with serious side effects for the individual. When the nervous system is deprived of its incoming information the consequences can be unpleasant.

When incoming impulses are completely prevented from reaching the second stage nerves, these nerves react by rapidly increasing their excitability. With no incoming messages due to the amputation or nerve transection, the second stage nerves start to fire off spontaneously, that is for no particular reason but just because they are over-excited. The leg nerves may be missing but all the central nervous system transmission nerves for the leg still exist. The areas of the brain looking after the missing part are still present and still capable of creating pain in that missing part.

Pain which appears in an area of the body which is now absent is known as phantom pain and is a common side effect of amputation which develops in the weeks and months after the trauma. Phantom pain can be very unpleasant in nature, very deep and cold, or sharp and stabbing and so can be a particularly difficult pain to treat or to cope with. Neuropathic pain is the term for a pain like this which is generated internally by the central nervous system and not as normal pains which are secondary to tissue damage.

Drug treatment of phantom pain is difficult as the morphine chemicals such as morphine, fentanyl, tramadol and codeine are often not very effective. The nerve treatment agents such as amitriptyline, gabapentin and pregabalin are used against neuropathic pain with some effectiveness. Other treatments include transcutaneous electrical nerve stimulation (TENS), an electrode based stimulation treatment which can be self-managed. Cognitive therapy may also be useful to start to cope with what can be a long term problem.

Amputation can be followed by a serious and hard to treat pain syndrome which may be more severe if there was a lot of pain in the limb before the operation was performed. Referral to pain clinic with its access to a multidisciplinary pain treatment team is a useful step.

About the Author:

Jonathan Blood Smyth is Superintendent of a large team of Physiotherapists at an NHS hospital in Devon. He specialises in orthopaedic conditions and looking after joint replacements as well as managing chronic pain. Visit the website he edits if you are looking for physiotherapists in Glasgow or elsewhere in the UK.