Objectives: Development of effective chronic pain treatment strategies has been hampered by the lack of an objective pain biomarker. Magnetoencephalography (MEG) has demonstrated cortical disorganization corresponding to the affected limb of complex regional pain syndrome (CRPS) patients and spinal cord stimulation (SCS) can acutely treat CRPS in a reversible and adjustable fashion. In order to better define a potential MEG-sensitive biomarker for chronic pain, our goal was to study the effects of therapeutic SCS on cortical disorganization in patients with unilateral limb CRPS.
Methods: Two patients treated with either thoracic or cervical SCS with leg or arm CRPS were studied with MEG. Baseline and tactile-evoked responses were recorded with and without effective SCS therapy.
Results: All MEG recordings were obtained with minimal interference. In the patient with arm CRPS, with the stimulator off, first and fifth digit primary somatosensory (SI) cortical representations (D1/D5) were significantly disorganized and spatially inverted as compared with the opposite unaffected limb. Effective SCS therapy was then able to acutely normalize or restore hand cortical organization in the affected CRPS limb. This restoration of cortical organization was partially maintained with lingering pain relief when the stimulator was subsequently turned off.
Conclusions: This is the first report of a MEG study showing D1/D5 cortical disorganization and its apparent reversal or restoration with cervical SCS therapy. Ours also is the first report of an apparent acute reversible interchange in the cortical representations of D1 and D5. Our limited data demonstrate that disorganization of SI cortex might be a neurophysiologic marker of chronic pain as shown with instantaneous normalization of SI disorganization or restoration of SI organization with therapeutic SCS. As a clinically proven tool for functional mapping, MEG might be shown to provide an objective measure of chronic pain. More data are required to further investigate this possibility.
Keywords: Biomarker; complex regional pain syndrome; magnetoencephalography; spinal cord stimulation.
© 2013 International Neuromodulation Society.