Mirror Therapy Needs Time to Work in Severe Phantom Pain

Daniel M. Keller, PhD

November 04, 2015

SANTIAGO, Chile — Failure of mirror therapy to relieve phantom limb pain may often be the result of insufficient length of treatment. The more severe the pain, the longer the time required, a new study indicates.

But even then, positive results should be apparent within about 3 weeks if the therapy is going to work, the researchers say.

"Mirror therapy actually does work, and it seems to have a very rapid response," said Jack Tsao, MD, DPhil, professor of neurology at the University of Tennessee Health Science Center in Memphis.

Mirror therapy in the past has produced inconsistent results, but new research using a systematic approach to the technique indicates that the degree of initial pain determines the treatment duration needed.

"The greater the pain starting, the longer treatment you have to give before you say it's not going to work or you give up on therapy," Dr Tsao said. "Our conclusion is that if you start with a mild amount of pain, you should be able to see a response in 1 week. If it's moderate, 2 weeks, and if it's severe, within 3 weeks."

 
The greater the pain starting, the longer treatment you have to give before you say it's not going to work or you give up on therapy. Dr Jack Tsao
 

In a presentation here at the XXII World Congress of Neurology, he said that phantom limb sensations, such as pain, itching, or being stuck in an uncomfortable position, occur in up to 95% of amputees, followed by gradual fading of the sensations. Pharmacologic therapies are generally ineffective.

The research, which Dr Tsao performed when he was at Walter Reed National Military Medical Center in Bethesda, Maryland, was a randomized, sham-controlled trial involving 22 lower-limb amputees. They were assigned to mirror therapy, mirror therapy with a covered mirror, or mental visualization.

The mirror group "moved" their phantom feet as they observed the reflection of their intact feet in a mirror placed between their legs, and the covered-mirror group moved their phantom feet while moving the intact ones. The mental visualization patients were asked to close their eyes and move their phantom feet.

Treatment was carried out for 15 minutes daily, 5 days per week for 4 weeks. The clinical endpoint was reduction in pain at 4 weeks, as assessed using a 100-mm visual analog scale (VAS). At week 4, the covered mirror and mental visualization groups crossed over to mirror therapy, and all groups continued mirror therapy through week 8.

Table. Median Score on VAS (100-mm Scale)

Time Point Mirror Therapy (mm) Covered Mirror (mm) Mental Visualization (mm)
Randomized trial      
   Day 1 30 33 43
   Week 1 14 36 59
   Week 2 15 44 48
   Week 3 7 47 46
   Week 4 6 36 60
Crossover to mirror therapy      
   Week 8 3 17 18

 

In a post hoc analysis of two independent cohorts of patients (n = 29), the researchers explored why some patients have not benefited from mirror therapy. Phantom limb pain was assessed on a 100-mm VAS and the McGill Pain Questionnaire–Short Form (SF-MPQ). Dunnett pairwise comparisons were made to compare scores on days 7, 14, and 20 with those on day 1.

By 1 week, scores declined significantly on the VAS (P < .003) and the SF-MPQ (P < .001). The benefits persisted at week 2 (P < .007 and < .001, respectively) and week 4 (P < .003 and < .001, respectively).

Initial pain scores were associated with the treatment time needed to see benefit. Patients with starting VAS scores of 60 or less (n = 19) had significantly lower pain by week 1. If the initial pain score was greater than 61/100, patients needed at least 2 weeks of mirror therapy.

It appears that most patients who benefit do so by 3 weeks. "This will hopefully help the therapist guide treatment, so if the mirror therapy doesn't work, they may try something else," Dr Tsao noted.

In response to a question from the audience, he reported that patients generally were receiving high doses of methadone or gabapentin (Neurontin, Pfizer).

"We found that the people in the mirror group were able to get off their methadone completely," he said. "Some of the people in the mental visualization group had to increase the methadone, but for the most part for the 4 weeks of the initial treatment they were able to not vary it very much."

The response appears durable, he commented to Medscape Medical News. In a 4-month follow-up, "we found that people's pain that had gone down had not had a recurrence. And subsequently, we saw people out to 2 years, and it had not recurred, so we think that for the most the treatment is extremely durable," he said. He noted that two people in another study experienced pain relief initially. When pain recurred, they restarted mirror therapy, which provided relief with no recurrence of pain.

"We believe the answer is...that you have to have both visual feedback and looking at either your own leg moving or your own arm moving reflected in the mirror while moving the phantom or looking at somebody else's limbs moving, or you could use a virtual avatar," he noted. He and colleagues are now testing a virtual avatar on a monitor screen, which appears to help phantom pain.

The researchers have found that patients have to start with slow motions so that the phantom limb can keep up with the intact limb in the mirror or with an avatar.

Using an avatar may help address the problem of phantom pain for double amputees. Dr Tsao said he has published about a lower-limb double amputee who watched and emulated the moving feet of a research assistant, "and we found that it was also effective in treating phantom limb pain." This finding has led to the idea of having a virtual reality system with an avatar's feet moving to help double-leg amputees.

Another interesting finding is that matching the sex, skin tone, or race does not matter for the therapy to be effective. "Having that limb moving is the critical piece," he said.

Zeroing in on Phantom Limb Pain

Various hypotheses have been proposed for the origin of phantom limb pain, including reorganization of the cerebral cortex with new neuronal connections, mismatched signaling in the neurons involved in vision and proprioception, and a phenomenon of "proprioceptive memory."

Dr Tsao said his finding are "consistent with the second theory of association of proprioception with vision because we have people closing their eyes and moving their legs, so the proprioception works when we took away vision."

Researchers have learned a lot over the past decade about phantom limb pain. "There's clearly a peripheral nerve input as well as a central nervous system interpretation of that peripheral nerve input," he said. By interrupting the peripheral sensory input (eg, with an anesthetic), the phantom pain goes away, but it comes back when the drug wears off.

Dr Tsao said that with mirror therapy, "the visual component is key…and there's a top-down driving effect." He hypothesizes that brain cortical regions can drive down the interpretation of the peripheral signal to the brain or that there is another kind of interplay.

Session moderator José Cuellar, MD, from the Center of Diagnostics and Rehabilitation and professor of neurology at the Catholic University of Bolivia in Santa Cruz, commented to Medscape Medical News that up to now, he has been aware of mirror therapy but has not seen such a systematic investigation of the technique as Dr Tsao and colleagues have done.

Although mirror therapy is not a standard treatment at this point, it is easy and inexpensive and may work rather quickly, so he said he will probably try it in his institution.

Dr Tsao plans to publish a treatment protocol for the administration of mirror therapy based on the available evidence.

There was no commercial funding for the study. Dr Tsao and Dr Cuerllar have disclosed no relevant financial relationships.

XXII World Congress of Neurology. Abstract 371. Presented November 2, 2015.

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