Unusual bilateral referred sensations in a lower limb amputee during mirror therapy: Evidence for a phantom limb within a phantom limb, and cross-hemispheric reorganization

Abstract

Background. Amputees often perceive sensations to be emanating from their missing limbs. Sensations can be evoked by touching an intact body part (“referred sensations”, RS) or by creating the visual illusion of an intact limb under volitional control (e.g. using a mirror image of one's intact, moving limb). Current findings suggest that RSs are associated with reorganization of the somatosensory cortex, with the area previously associated with the limb now responding to stimulation of the adjacently mapped body area (Ramachandran, Flor). We report a rare example of bilateral RS that is evoked by mirror stimulation, and that may imply long-range, cross-cortical remapping. Method/Results. Bilateral RSs were elicited from a 50 y/o male above-the-right-knee amputee whenever he viewed his intact leg in a mirror (treatment for phantom limb pain). (1) In the absence of mirror stimulation, he experienced a paralyzed phantom right leg with pain in the toes and no RS. (2) Mirror stimulation elicited movement and tingling sensations, and transient pain suppression. (3) If during mirror stimulation, he was touched on his lower left leg or foot, he felt stimulation at equivalent sites in BOTH limbs. (4) The bilateral effect lasted for up to a minute after removing the mirror. (5) The mirror illusion caused RSs of his right foot and lower right leg on his LEFT knee. That is, touching the back and front of his LEFT knee evoked RSs perceived to emanate from his phantom RIGHT foot and knee. Discussion. These rare phenomena are inconsistent with simple remapping of adjacent cortical areas in this subject. It seems likely that the right somatosensory cortex (which normally controls the left leg) now controls the corresponding left cortex that formerly controlled the right leg. A neuroimaging study could establish if stimulating the left leg activates bilateral cortical areas.

Footnotes

 Department of Veterans Affairs F6441R.