Virtually all amputees experience ongoing sensations in their missing limb, and many also experience intense pain: phantom limb pain. How on earth can you treat pain in a body part that doesn’t exist? And what is causing the pain in the first place?

Many amputees feel ‘phantom’ pain in their non-existent limbs. Image credit David Ingram via Flickr

The pain is real

One of the most famous examples of a phantom limb belonged to Lord Horatio Nelson, a much-decorated British Naval officer. In 1797, he had to have part of his arm amputated after it was shot in battle. He went on to experience severe pain in his missing arm and hand, including the sensation that fingernails were digging into his palm. Nelson used this experience to argue for the existence of the soul: if his arm could ‘survive’ being destroyed, why not an entire person?

Phantom limb pain is extremely common. In a study of 5000 veterans post amputation, 78% experienced it. Sufferers explain that a phantom limb can experience all the same sensations a real limb can: pain, heat, sweating, tingling, paralysis and movement. And phantom sensations don’t only occur in limbs. Up to 80% of women experience phantom breast pain after a mastectomy. Some women also report a phantom uterus with monthly cramps after a hysterectomy.

Perhaps one of the only vaguely similar experiences non-amputees can have of phantom pain is after a local anaesthetic at the dentist. Your nerves go dead, but you don’t feel like your lips and cheek have disappeared. If anything they feel swollen and puffier than usual.

All in the mind

At first glance, phantom pain seems exceedingly odd – and that’s putting it mildly. How can a body part that doesn’t exist experience pain? But if we think about what pain actually is, phantom pain becomes easier to understand. Put very simply, pain is a perception similar to hearing or smelling. If you break your arm, nerve cells in your arm send a message to your spinal cord and then onto the brain to indicate there’s a problem. Your brain translates this message and perceives the feeling of pain. The pain is in your brain.

For a long time, it was thought phantom limb pain derived from inflamed, irritated or frayed nerve endings in the stump sending incorrect messages to the brain. In the past, doctors sometimes performed surgery to remove more of the stump in the hope of fixing the problem. But it didn’t work.

Your plastic brain

Our current understanding of phantom limb pain highlights how extraordinary our brains are. Inside your brain is a virtual, sensory model of your body. In effect, your brain contains a map of your body, but composed of brain cells. Each of your body parts has a corresponding section of the map in your brain. Research suggests that if some parts of the map are inactive (for example, as a result of amputation), adjacent areas of the map begin to take over. So the nerve connections in the brain become reorganised and that’s what we refer to as brain plasticity.

Researchers have shown the part of the brain’s sensory map that used to represent the now-amputated limb can be taken over by representations of different body parts. In the case of arm amputations, the areas that have been found to take over are the face and lips. This is because in the brain’s map, the face and arm areas are right next to one another. This means touching an affected person in particular places on the face results in corresponding feelings in the phantom limb. Scientists have been able to draw on the faces of amputees (literally, with a texta), to show where the missing limb and digits are felt.

Gaming to tackle pain

For many years, phantom limb pain proved incredibly difficult to treat. Drugs don’t tend to work. How do you treat pain that is perceived to occur in a body part that doesn’t exist? Of course, you don’t; you treat the brain, which is where the sensations originate.

One of the first successful treatments for phantom limb pain is deceptively simple, and impressively cheap. In some cases, all that is required to retrain the brain is a mirror. Mirror therapy provides the brain with an opportunity to match what it sees with what it feels. A person suffering from phantom limb pain can position a mirror so that the reflected limb seen in the mirror appears to be the amputated limb. The limb can be moved and stretched and many people have reported huge reductions in pain as a result.

A slightly higher-tech and very promising treatment for phantom limb pain is augmented reality. This technology enables a wider range of motion of the replacement limb and incorporates gaming to keep patients motivated to do their exercises. Truth be told, we don’t fully understand why these treatments work. But whatever extraordinary brain tricks are going on, I’m guessing phantom limb pain sufferers will be happy to play the game.

Links and stuff

• Plethrons video: Phantom pain explained
• The Good Stuff video: What causes phantom limbs?
• News video: treating phantom limb pain with mirror therapy
• TED talk: three clues to understanding your brain