Additive Analgesic Effect of Transcranial Direct Current Stimulation Together with Mirror Therapy for the Treatment of Phantom Pain

Abstract

Objective Current analgesic treatments for phantom pain are not optimal. One well-accepted yet limited nonpharmacological option is mirror therapy, which is thought to counterbalance abnormal plasticity. Transcranial direct current stimulation (tDCS) is an emerging approach believed to affect the membrane potential and activity threshold of cortical neurons. tDCS analgesic effectiveness, however, is mild and short, rendering it a noneffective stand-alone treatment. This study aimed to assess if a combination of mirror therapy with tDCS results in a superior analgesic effect as compared with mirror therapy alone in patients suffering from phantom pain due to recent amputation. Design Following ethical approval, eligible patients provided informed consent and were randomly assigned to a study treatment group that continued for 2 weeks (once daily): 1) mirror therapy; 2) mirror therapy and sham tDCS; or 3) mirror therapy and tDCS. Assessments were done before treatment; at the end of treatment weeks 1 and 2; and at 1 week, 1 month, and 3 months following treatment. The primary outcome measure was pain intensity. Secondary measures were derived from the Short Form McGill Pain Questionnaire and the Brief Pain Inventory. Results Thirty patients were recruited, and 29 patients completed the study. Three months following treatment, pain intensity was significantly (P<0.001) reduced in the combined treatment group (reduction of 5.4±3.3 points) compared with the other study arms (mirror therapy, 1.2±1.1; mirror therapy and sham tDCS, 2.7±3.2). All secondary outcome results were in line with these findings. Conclusions Combining tDCS with mirror therapy results in a robust long-lasting analgesic effect. These encouraging findings may contribute to the understanding of the underlying mechanisms of phantom pain.

Time since onset might be of essence: A recommendation to assess the effects of combination of non-pharmacological neuromodulatory approaches at early stage since symptoms onset

“…All the studies used a combination of tDCS and another non-pharmacological neuromodulatory approach. In all studies, the tDCS intensity was set to 2mA, except for Segal et al (12), which used 1.5 mA. In all the studies, the tDCS duration was 20 min, except in 16), in which posttreatment pain intensity was measured at the end of treatment (and not 1 month later) because follow-up data at 1 month were unavailable.…”

“…The other neuromodulatory approaches that were combined with the tDCS could be grouped into 4 categories: The first category includes mirror therapy (12)(13)(14)(15), visual illusion (16- 18,22) and motor graded imagery (24). These three interventions…”

“…To address this hypothesis, researchers began to explore the analgesic effects of such combined treatments in various pain indications, including phantom limb pain ( 12 – 14 ), neuropathic pain ( 15 – 23 ), complex regional pain syndrome ( 24 , 25 ), fibromyalgia ( 26 – 33 ), headache ( 34 ), chronic musculoskeletal pain ( 35 ), chronic low-back pain ( 36 – 40 ), knee osteoarthritis pain ( 41 – 45 ), temporomandibular disorders ( 46 ), burning mouth syndrome ( 47 ), chronic visceral pain ( 48 ), neurogenic pain ( 49 ), myofascial pain ( 50 , 51 ), tendinopathy ( 52 ), and radiculopathy ( 53 ) ( Table 1 ).…”

“…The other neuromodulatory approaches that were combined with the tDCS could be grouped into 4 categories: The first category includes mirror therapy ( 12 – 15 ), visual illusion ( 16 – 18 , 22 ) and motor graded imagery ( 24 ). These three interventions are sharing similar characteristic—in all these behavioral tasks the participants receive (or imagine) visual input (with, or without additional sensory-motor input) that is assumed to counterbalance the maladaptive plasticity associated with the painful condition.…”

French guidelines for neuropathic pain: An update and commentary

“…Interestingly a recent RCT combining transcranial direct current stimulation (tDCS) with mirror therapy showed that it resulted in higher pain reduction than mirror therapy alone in phantom limb pain [33]. Validation of the best combination has still to be investigated.…”