By Cmdr. Jack Tsao, director of Traumatic Brain Injury programs at the U.S. Bureau of Navy Medicine and Surgery.
In the last five years, through my academic affiliation appointment at the Uniformed Services University, I’ve had the opportunity to work with some amazing people at Walter Reed Army Medical Center including Col. Paul Pasquina (head of Orthopaedics and Rehabilitation) and Col. (ret.) Charles Scoville to examine why Mirror Therapy seems to be an effective treatment in what is a common phenomenon in Wounded Warriors with amputation: Phantom Limb Pain (PLP).
Phantom Limb Pain is the sensation that a limb is still present and experiencing pain following amputation and occurs in 90 percent of amputees. Often an amputee begins to experience this phenomenon immediately after surgery; this is typically followed by a gradual fading of the limb from memory. Patients frequently report that this phantom limb is stuck in an uncomfortable position or has the sensation of pain, electric shocks, or itching. There are an infinite variety of sensations associated with PLP, from merely uncomfortable to debilitating, but they have one thing in common: pharmacologic therapies are generally ineffectual.
Besides trauma, PLP can and often does accompany an amputation of an arm or leg due to cancer, diabetes or other causes. One can also have, for example, phantom breast pain after a mastectomy. Research explains why this is a neurologic phenomenon not “psychiatric.”
There are three main theories for why PLP occurs:
Phantom pain may be due to mismatched signaling in the neurons responsible for vision and proprioception, or the sense a limb’s position in 3-dimensional space. The neurons controlling the limb, which are still intact after amputation, do not match up to visual signals that tell the brain the limb is no longer there. The brain then interprets the conflicting signals as the phantom limb is still present and experiencing pain.
The second theory is that phantom pain may be due to aberrant new brain neuronal connections. It’s not clear how these new connections would mediate pain, but studies have shown that the more extensive the new connections are the more severe the pain is.
Finally, phantom pain may be due to a phenomenon termed “proprioceptive memory.” We think there may be stored memories of various limb positions and when the phantom is experienced the brain draws on the memories of the limb’s position.
I think that all of these theories are valid to varying degrees. It may be that some combination of these theories explains PLP, but the origins are still not fully elucidated.
Let’s say a patient complains that “my phantom hand [or foot] is often stuck in a painful uncomfortable position,” or maybe “the fingernails of my phantom hand are digging into my phantom palm.” Mirror therapy has proven to be an effective and simple treatment for many such cases.
Mirror therapy first came to my attention when I saw a 1995 study by V.S. Ramachandran and colleagues at the University of California, San Diego that stated 60% (9 out of 15) of their patients in a small case series showed improvement in PLP symptoms after mirror therapy. His study group consisted a small series of upper-extremity amputees who were years to decades post-amputation.
Mirror therapy uses a flat mirror placed parasagittally along the patient’s body so that when the patient moves the intact limb, the mirror provides the optical illusion that the phantom limb is moving at the same time.
There were, however, no controlled trials of mirror therapy for phantom limb pain after the 1995 study, until my colleagues and I conducted one, funded by the Military Amputee Research Program.
In our clinical trial, we designed a randomized, sham-controlled trial of mirror therapy and mental visualization therapy for lower extremity amputees with PLP. Volunteer subjects were randomized into three groups, each using a different therapy: mirror, covered mirror and mental visualization. Mirror therapy subjects moved their phantom leg/foot while observing a reflection of the intact leg/foot moving in a mirror, covered mirror subjects moved their phantom leg/foot while moving their intact leg/foot (but the mirror was covered by a white bed sheet, and mental visualization subjects were asked to close their eyes and move their phantom leg/foot.
The treatment went on for 15 minutes a day, five days a week over a period of four weeks. Covered mirror and mental visualization subjects were then offered the opportunity to switch over to mirror therapy for another four weeks. Some of our conclusions after our initial trial were:
- Mirror therapy is more effective than covered mirror or mental visualization therapies
- 6 of 6 mirror and 8 of 9 cross-over subjects improved on mirror therapy – total 14 of 15 (93%) subjects improved
- The first noticeable change was a decrease in the intensity of the pain, followed by a decrease in the length of each episode and then the number of daily episodes.
- Side effects – 2 subjects in the mirror group had brief grief reactions, none in covered mirror or mental visualization groups had grief reactions, even after crossing over to using mirror
Mirror Therapy is now used at all three of our military amputee centers: Walter Reed Army Medical Center in Washington, DC, Brooke Army Medical Center in San Antonio, TX, and the Naval Medical Center San Diego, San Diego, CA.
I’m extremely gratified for the support of the rehabilitation staff at Walter Reed Army Medical Center and especially our brave wounded warriors who volunteered for a clinical trial not knowing if the treatment they were being randomized to would help treat their pain.
Although mirror therapy has helped many patients (both military and civilian), it doesn’t help everyone. To better understand what is happening to the brain when mirror therapy is used, we have now started functional magnetic resonance imaging to map out brain activation patterns in patients treated with mirror therapy. We hope to have preliminary results soon. Also since there appears to be a small percentage of amputees who never develop PLP, we are investigating whether there might be a genetic component mediating the development of PLP.