Assessment of reorganization in the sensorimotor cortex after upper limb amputation

Objective: We wanted to investigate plastic changes occurring in the motor and somatosensory cortex after upper limb amputation, and their possible relationship to phantom pain. Method: To assess these plastic changes, we used transcranial magnetic stimulation (TMS) and source localization of somatosensory evoked potentials (SEP). Eleven patients with upper limb amputation were investigated. The phantom pain intensity was assessed by visual analogue scaling (VAS). Results: Using TMS mapping, we found a significant lateralization of the amplitude-weighted centre of gravity (P<0.01) and an enlargement of the excitable area (P<0.05) on the hemisphere contralateral to the amputation. SEP mapping showed a significant medialization of the N20 dipole (P<0.05) on this side. None of these changes correlated with the phantom pain intensity. Conclusions: We conclude that after limb amputation, the relationship between plastic changes occurring in the sensorimotor cortex and phantom pain seems to be more complex than previously believed.