the phantom pain science project


My 10 year-old, much to my simultaneous delight and chagrin, is an intellectually curious child. I say delight because he actually thinks about things and follows them down whatever rabbit hole they may lead him into; chagrin because, as is the case with his latest project, it requires me to get involved with a large piece of cardboard that will stand atop a table at his school’s gym proudly announcing what his scientific inquiry teaches us.

I do not like creating science fair presentations. I dislike them so much that I actually begged my wife to take the lead in cutting out colorful letters and organizing materials on the aforementioned cardboard.

However, my son’s topic this year is of particular interest to me and people in the limb loss/difference community: phantom pain. He’s obviously been turning this one over in his head for a while, having heard me complain about my (blessedly) sporadic battles with jolts of electricity firing down my absent left leg.

The threshold question here was how to do a fifth-grade science project addressing the topic. Even with my contacts, there’s not a bevy of amputees lining up to participate in such an activity. Moreover, hacking the limbs off his friends to create a captive amputee population wasn’t likely to get Independent Review Board approval. Faced with these logistical challenges, he opted to create a mirror box, explain how mirror therapy works, and give a review of what the current literature tells us about this treatment for phantom pain.

Unfortunately, most clinical research around the subject is written at a slightly higher than fifth grade level. As a result, I’ve been reviewing the literature for him so that I can help explain what it all means. As I was doing this, it occurred to me that a discussion of some of the more current published works might be of interest to the less is more community. So you can all thank my son for this post.

what mirror therapy is

In its simplest form, mirror therapy involves tricking your mind into seeing your amputated limb as whole again. Since the early 1990’s, researchers have been playing with mirrors in an effort to understand how viewing two intact limbs affects the severity, duration, and number of episodes of phantom pain.

The tool of choice for this process – developed largely in connection with the study of upper extremity amputees – is a mirror box. While some enterprising entrepreneurs have gone so far as to start selling these devices, they’re stupefyingly simple to construct. All you need is a cardboard box big enough to fit your hand into – don’t worry lower extremity amputees; I’ll get to you soon enough – a 12″ x 12″ mirror (available at your local Home Depot) and some duct tape.

Your instructions, in their entirety, are this: duct tape the mirror to the outside of the box. (Thank God my son picked the one project involving construction that even I can’t screw up. Anything more complex than this and, sadly, I would’ve had to call in reinforcements.)

This is what it looks like when finished:

You put the residual limb in the box so that you can’t see the end of it and position your head so that it’s looking at the mirror. You then move your sound limb and focus on its mirror reflection wiggling its fingers, rotating its wrist, etc., while imagining doing the same thing in the phantom limb.

(Note: this box is really much larger than it has to be. But my friends at the Home Depot had limited supplies that day. Also, when performing mirror therapy as an upper extremity amputee, it’s important to remove any watches or jewelry from your sound hand/wrist to make the illusion as realistic as possible.)

For you lower-limb amputees who are saying, “this is brilliant, but creating a box the length of my leg and attaching a mirror to it is going to be a real drag,” your solution is much simpler:

It works by simply placing the mirror between your legs like so and moving your ankle and toes while looking at the reflection:

(Note: this would be done while wearing shorts and no shoes or socks, so that you can see your ankle and toes.)

This, in its simplest form, is mirror therapy.

what the research tells us

The most noteworthy aspect of phantom pain is how little is still understood about  it. The general consensus in the literature is that at least two-thirds of people with LL/D experience phantom limb pain. (Abbreviated to “PLP”, probably because researchers didn’t want to abbreviate it to “PP” for fear of not being taken seriously. I have no such foibles, and since one of my primary goals is to entertain, we will refer to it as PP for the rest of this article. My 10-year-old scientist son will also find this enormously funny.)  There also appears to be general agreement that people who undergo traumatic amputations or who have elective amputations after suffering from painful pre-existing conditions for extended periods of time are more susceptible to PP.

One of the foremost authorities in the area and a leader in mirror therapy research, V.S. Ramachandran, has summarized no less than five different explanations for why people have PP (isn’t this abbreviation fun?) in an article discussing the history of mirror therapy:

  1. irritation of curled up nerve endings (neuromas) and scar tissue in the residual limb;
  2. low-threshold touch inputs cross-activating high-threshold pain neurons [if I understood what that meant, I’d dumb it down; I don’t, so I can’t];
  3. remapping of the brain post-amputation leading to chaotic “junk” output that registers as pain;
  4. a mismatch between motor commands and the expected but missing visual and proprioceptive input manfesting as pain (i.e., your brain is telling you to do one thing but your eyes are seeing and your body is perceiving something different); and
  5. preamputation pain persists as a memory in the phantom limb.
Ramachandran’s research of PP includes a history of fascinating discoveries, like how tapping an upper-extremity amputee’s cheek in specific places is felt as tapping on the phantom limb. More detailed exploration revealed that very specific parts of the face track to each finger in the phantom limb. And it works both ways: studies of people who had a nerve cut in their face so that they couldn’t feel their cheek learned that touching their fingers and hands registered as being simultaneously touched on the face. (This isn’t all that relevant to the main topic, but so damn odd that I just had to work it in.)

If one of the leading researchers on the subject can’t definitively state what PP is [good one!], it’s not surprising that the reasons for mirror therapy’s apparent benefits aren’t yet fully understood. In what amounts to a scientist throwing up his hands and saying, “I don’t f#@!ing know,” a 2011 case study states, “The mechanism behind mirror therapy’s effect on [PP] is yet to be clearly defined.” Or, put more simply, “We know that mirror therapy seems to work, but we really don’t know why.”

While still in its infancy, mirror therapy research has shown remarkable promise. In a letter to the New England Journal of Medicine, researchers from the Department of Defense/V.A. described their work with 18 lower extremity amputees. They divided the 18 participants into three groups: a group that received mirror therapy; a group that performed exactly the same regimen but with a covered mirror; and a group that performed mental visualization instead of using a mirror or covered mirror.

Over the course of four weeks, participants had daily sessions lasting 15 minutes. They were asked to track the number of painful episodes, the duration of those episodes, and the intensity of the pain experienced. While the sample size was small, the results were noteworthy.

All of the mirror therapy patients reported a decrease in the number of painful episodes, the duration of those episodes, and the pain intensity. In contrast, half of the subjects in the covered mirror group experienced an increase in PP, while only one individual reported a decrease. In the mental visualization group, two-thirds of the participants reported an increase in PP, while one-third reported a decrease. Finally, 9 of the subjects from either the covered mirror or the mental visualization group later transferred to mirror therapy. All but one reported a decrease in PP as a result of the mirror therapy.

The researchers concluded, in a vein similar to that previously mentioned, that “[a]lthough the underlying mechanism accounting for the success of this therapy remains to be elucidated, these results suggest that mirror therapy may be helpful in alleviating phantom pain in an amputated lower limb.”

In the case study referenced earlier, researchers at the Naval Medical Center, San Diego, published their findings regarding four traumatic below-knee amputees, all of whom had undergone extensive limb salvage procedures before amputation, and who had experienced significant pain and loss of function following those limb salvage efforts. Put simply, the four subjects were, based upon the current understanding of PP, uniquely predisposed to experience significant and debilitating PP post-amputation.

In the case study, the subjects – all of whom elected to undergo a below-knee amputation – engaged in mirror therapy for two weeks before undergoing their amputation. By giving the therapy prospectively, the researchers hoped to test whether pre-surgical mirror therapy could reduce post-surgical PP. The results, again, were promising. At the one-month mark, none of the subjects were experiencing regular or severe PP.

conclusions

When I returned home from the hospital after my amputation, I was given a TENS machine (electrical stimulation) and a hand-held massager to try and stop the PP. (I was decidedly less happy about either of these solutions than I had been with my little round friend, Percocet, which the doctors cut me off from almost immediately upon being discharged.) Neither worked particularly well.

I tried to cope with PP largely through distraction. I read lots of books – lots – late at night when the pain seemed to visit most regularly. However, what was always amazing to me was that as soon as I got my first prosthesis and I could see a shoe on the floor where my left foot had always been, the PP disappeared, and the nearly-constant phantom sensation (as opposed to pain) became an infrequent issue. The prosthesis – especially when under long pants – was my mirror.

The next time I’m up late at night, feeling those excruciating lightning bolts firing down my leg into the foot that doesn’t exist, I’m going to find my way to my son’s fifth grade science project – which will be kept for this purpose – and see what happens. I hope that won’t be any time soon, but I will report back to you when it does happen.

In the meantime, further research around mirror therapy’s efficacy in treating PP will continue to get published, and I’ll keep the less is more community posted on new data as it becomes available.

——————————————————-

In the interest of full transparency, here are the formal citations to the 3 pieces linked to in this post:

The use of visual feedback, in particular mirror visual feedback, in restoring brain function, Ramachandran et al., Brain 2009: 132; 1693-1710.

Mirror Therapy for Phantom Limb Pain, Chan et al., N. Engl. J. Med. 2007; 357: 2206-07

Preamputation Mirror Therapy May Prevent Development of Phantom Limb Pain: A Case Series, Hanling et al., Anesthesia & Analgesia, Vol. 110, No. 2, February 2010, pp 611-14.

4 thoughts on “the phantom pain science project

  1. In a mirror therapy paper written in German and by a physiotherapist of the St. Gallen Cantonal Hospital, I actually read what I experienced about a year earlier – that you MUST be able to at least wiggle your phantom limb for the mirror to at least halfways work. If your phantom limb is entirely rigid and stiff, hard and non-moveable (mentally, that is) then you can mirror all day long and all you may get is more phantom pain. So it made things worse for me, but just a bit, enough to notice, not massively worse. There are other theories about phantom pain whose understanding help me better, I must say. Now, seeing as if phantom pain is as hard to disprove as it is to prove, there are not many things one can do to really find out about it. In my perception, any halfways attractive female therapy person will blow phantom pains away – with or without mirror and no matter what else. A large amount of that type of confounding effects – in my view – makes it entirely impossible to distinguish between placebo and effective neural remodeling effect, which, in order to be recognizeable as that, will maybe even take some time until it becomes noticeable. Whereas placebo can be effective imnediately.

  2. Pingback: to be or not to be (15 years) « less is more

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