| Abstract No.: | B-D2143 |
| Country: | Canada |
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| Title: | RELIABILITY OF TRANSCRANIAL MAGNETIC STIMULATION MOTOR MAPS OF STUMP MUSCLES IN UPPER LIMB AMPUTEES |
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| Authors/Affiliations: | 2 Séabastien Hétu*; 2 Martin Gagné; 1 Karen T Reilly; 2 Joëlle Dubé; 2 Catherine Mercier;
1 Center for Cognitive Neuroscience, CNRS, Lyon, France; 2 CIRRIS/Université Laval, Québec, QC, Canada
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| Content: | Transcranial magnetic stimulation (TMS) motor mapping is used extensively to assess cortical plasticity in numerous clinical populations and following various interventions in rehabilitation. In all of these contexts, changes in various TMS measurements are taken as indicators of reorganization within the motor system. However, accurate interpretation of muscle representation changes relies upon the stability and reliability of TMS measures. While several recent studies have investigated the test-retest reliability of TMS measurements, none have examined the stability of motor maps in neurological populations.
Objective: The aim of our study was to assess the reliability of several TMS parameters in amputees. As phantom limb sensations (such as pain and ability to move) are known to fluctuate from day to day, we wanted to know whether the reliability of amputees’ motor maps was comparable to that of healthy individuals’ maps.
Material and Method: Six male traumatic amputees with above-elbow amputation were tested on two separate sessions (0.5 to 7 days apart, with a median interval of 1 day). TMS mapping was performed at rest for the biceps (n=5) or the deltoid muscle (n=1) using a figure-of-eight coil and a Magstim 200® stimulator. Four stimulations at 120% of motor threshold intensity were delivered to each of fifteen points forming a 3x5 grid over the primary motor cortex (M1) controlateral to the amputation. Using the BrainSightTM system, we co-registered the subject’s head with their MRI image to ensure optimal coil positioning. The motor threshold at rest (rMT), response latency, and several map parameters such as center of gravity (CoG) and map volume were assessed. Intra-class correlations (ICC) were used to assess the reliability of these variables.
Results: Resting motor threshold (ICC = 0.99) and response latency (ICC = 0.95) measures were highly reliable. We found an average difference between the two sessions of 1.67 % for the rMT (range = 0 - 4 %) and 0.56 ms for the latency (0.13 to 1.35 ms). Mapping parameters were moderately to highly reliable. CoG position in the medio-lateral plane was highly stable (ICC = 0.85), with an average difference between sessions of 2.57 mm (range = 0.2 - 4.2 mm). Map volume was moderately reproducible with an ICC of 0.57.
Discussion: Our data indicate that, as in healthy subjects, several TMS parameters are reliable in amputees. The intra-class correlations revealed a high reliability between the two sessions for the majority of parameters. It seems, therefore, that even with massive neurological changes due to reorganization in the motor cortex following amputation, TMS measures remain stable across time (at least in the range of 1 – 7 days). In light of these results, TMS can be used to study amputation-induced plasticity or to measure the effects of rehabilitation interventions. Further research is necessary bettering order to describe the reliability of TMS parameters in other neurological populations such as stroke patients, as well as across longer time periods.
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