Researchers at Oxford University say the “phantom pain” felt by many amputees after losing a limb may trick the brain into thinking the limb is still there.
Phantom limb pain is a common and painful disorder that many amputees suffer long after their limbs are removed. The origin of the pain and sensations from the missing limb are not well understood.
“I can feel my fist clenching, my fingernails digging in. I can see the hand isn’t there but the sensation is so realistic,” says 22-year Kirsty Mason, who lost her right arm in an accident at a train station four years ago.
“I get the usual pins and needles and a constant niggling pain that I can shut out by doing other things. But the worst pain is a kind of burning,” Mason says. “It sounds silly, but the only thing I can do is stick my hand in a freezer. It numbs it.”
Until now it was thought that “plasticity” or changes in the brain connected with the missing limb drove phantom pain. But the Oxford study published in the journal Nature Communications suggests the opposite – that pain is driving plasticity.
“Almost all people who have lost a limb have some sensation that it is still there, and it’s thought that around 80% of amputees experience some level of pain associated with the missing limb. For some the pain is so great it is hugely debilitating,’ says lead author Dr. Tamar Makin of the Centre for Functional Magnetic Resonance Imaging of the Brain at Oxford University.
Oxford researchers used magnetic resonance imaging (MRI) to study the brains of 18 people who had phantom pain after an arm was amputated. They compared the brain scans of the amputees to brain scans of 11 people born without a hand and a control group of 22 adults with two full limbs.
Although the amputations had been done 18 years earlier on average, participants still felt sensations for the missing arm. By asking them to move the fingers of the phantom limb while in the MRI scanner, the researchers were able to see how brain processed the imaginary movement.
They found that the brain still maintained a representation of the missing hand. The extent of the representation was linked to the strength and frequency of the phantom pain. Those feeling the greatest pain retained the strongest representation of the missing hand.
‘We were astonished to find that in amputees experiencing strong phantom pain, the brain’s response was indistinguishable from that seen in people with intact limbs,’ says Makin.
The researchers hope their study of the brain could lead to the development of new treatment options for phantom pain.
Currently painkillers do little to relieve the pain of amputees like Lynn Ledger, a 48-year old therapist in Nottingham, UK. Her left arm was amputated above the elbow in 2009 after radiotherapy for a rare form of cancer in the arm failed. Ledger, who participated in the Oxford study, still feels severe pain as if it was coming from the missing limb.
“I’ve pretty much tried everything to deal with the pain but nothing has worked,”’ Ledger says. “There are no drug treatments that work because the condition is not fully understood yet. I can only use various distraction techniques, breathing exercises and mental imagery techniques, to help me manage the pain.”
‘It’s very hard to describe the pain to others. I have a nonexistent limb, but I still sense it and feel pain,” Ledger explains. “Imagine you are wearing a lady’s evening glove that stretches from the fingers up the arm past the elbow. But everywhere the glove covers, it’s as if it’s constantly crushing your arm. There are also shooting pains and intensely painful burning sensations that come and go, but the crushing pain is constant.”
While the Oxford researchers have found brain changes that are correlated with phantom limb pain in this study, they cannot tell if they are causal. To get a better understanding of that, they are beginning a trial with people who lost an arm through amputation to see if brain stimulation can influence the phantom pain they experience.
The brain stimulation uses a tiny electric current from two electrodes placed on the head to try and boost the connection of the phantom limb area of the brain to the rest of the brain cortex.