April Flowers for redOrbit.com – Your Universe Online
A new brain imaging study from Oxford University reveals that the phantom pain many amputees feel in the missing limb is linked to changes in the brain that occur following amputation.
Arm amputees who maintained strong representations of the missing hand in their brains — to the point where it was indistinguishable from persons with both hands — experienced the most phantom limb pain.
The research team hopes that their identification of brain responses correlated with the level of phantom pain will increase understanding of how the brain reorganizes and adapts to new situations, as well as aiding in the development of treatment approaches for amputees.
“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 Dr Tamar Makin of the Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB) at Oxford University.
Current treatments for phantom limb pain tend to be limited to standard drugs for pain relief, however, the origin of the pain is not well understood. Many factors might lead to the pain, including injured nerve endings at the site of the lost limb or changes in the brain regions connected with the missing limb.
Previous thought held that the brain reorganization, or plasticity, following amputation involved the hand area being recruited to control other body parts. Suggestions have been made that this plasticity and recruitment might be involved in the phantom pain. In other words, the reorganization was driving the pain. The Oxford team suggests the opposite might be true instead — the pain is driving the plasticity. Experiencing frequent and strong pain could lead the brain to maintain its representation of the missing limb.
One participant in the study, Lynn Ledger, is a 48 year old trained therapist and advisor to charities on management training from Nottingham, UK. In May 2009, Ledger had her left arm amputated halfway between the elbow and shoulder after radiotherapy for a rare form of cancer failed to resolve an extensive tumor in her arm. Ledger experiences severe phantom pain in the missing limb.
“I’ve pretty much tried everything to deal with the pain but nothing has worked,” Lynn 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. It’s like: 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.”
“When I heard about this study I wanted to be involved as it was trying to improve people’s understanding of the condition.”
Kirsty Mason from Bracknelll, UK also participated in the study. Mason, 22, is about to start a new job as a support worker for persons with mental health problems. She is also an assessor for disabled students for their assisted technology needs. Mason lost her right arm four years ago just below the elbow after blacking out and falling onto the rails at a train station. She woke to find the wheel of a train stopped on her arm. In the intervening four years, she has learned to write with her left hand, and last year she began driving again.
“With me it’s all or nothing,” Mason says of her phantom pain. “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. It’s less frequent but it’s intense: 90-100 on the scale. It sounds silly, but the only thing I can do is stick my hand in a freezer. It numbs it. I can feel my fist clenching, my fingernails digging in. I can see the hand isn’t there but the sensation is so realistic. If someone throws me a ball, I’ll move both hands to catch it. I’ll put out both hands if I fall over.”
To study how the phantom limb pain felt by people who have had an arm amputated is related to changes in the brain, the team from Oxford used MRI imaging. The team compared MRI data of three groups. The first consisted of 18 amputees with differing levels of phantom pain. The second group consisted of 11 persons born with one hand through a limb deficiency. The final, control, group consisted of 22 adults with two full limbs.
On average, the amputations were done 18 years ago. The participants still experienced sensations for the missing arm, however. The researchers asked them to move the fingers of the phantom limb while in the MRI scanner, allowing them to look at how the missing hand is represented in the brain.
The scans revealed that the brain maintained its representation of the hand, even though the limb was no longer present. The team was able to link the extent to which the representation was maintain to the strength and frequency of the pain the amputees felt. In other words, the more pain a person felt, the stronger the representation of the missing hand in their brain.
“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 Dr Makin.
The amount of grey matter in the phantom hand region of the brain associated with the phantom hand was reduced in amputees compared to those with two full hands. The researchers again linked this to the amount of pain felt, with those experiencing the strongest pain showing less structural degradation in the brain.
While those with strong phantom limb pain maintained the local brain structure and function for the missing hand, however, evidence revealed that connections to other parts of the brain were disrupted more. Specifically, the representation of the missing hand was more out of synch with the area looking after the other hand on the opposite side of the brain.
Dr Makin says, “Most people experience “phantom” sensations in a missing limb after amputation. This disconnect between the physical world and what they are experiencing appears to be linked to a functional detachment in the brain. There seem to be reduced connections between the missing limb part of the brain and the rest of the cortex that’s involved in movement. Our results may encourage rehabilitation approaches that aim to re-couple the representation of the phantom hand with the external sensory environment.”
The researchers are unable to tell if these brain changes are causal. To gain a better understanding, they are initiating a new trial with individuals who’ve had an arm amputation to see if a brain stimulation technique can influence the phantom pain. The team will take MRI scans before, during and after the technique.
This new technique employs a tiny electric current from two electrodes placed at appropriate sites on the outside of the head to try and boost the connection of the phantom limb area of the brain to the rest of the cortex.
The findings of this study were published in a recent issue of Nature Communications.
Image 2 (below): An amputee suffering from phantom pain maintains a representation of the phantom hand in their brain. Credit: Oxford University