Paresthesiae during radiofrequency neurolysis of lumbar sympathetic trunk in CRPS: human evidence of a sympatho-sensory connection?

Radiofrequency heat lesioning has been advocated to prolong the duration of therapeutic effect of lumbar sympathetic block in Complex Region Pain Syndrome (CRPS) of the lower extremity. Prior to radiofrequency lesioning of the lumbar sympathetic trunk, sensory and motor stimulation may be used to verify that the active needle tip is not adjacent to a spinal nerve to avoid unwanted neural injury. However, the value of sensory stimulation to aid in precise needle positioning at the desired target remains controversial. In this report we describe our observations using sensory stimulation to aid in needle placement for radiofrequency lesioning. We confirm a novel observation that paresthesiae to the lumbar sympathetic trunk is possible and hypothesize on pathophysiologic meaning. Two representative patients are presented who underwent sensory stimulation of the lumbar sympathetic trunk during needle placement for lumbar sympathetic radiofrequency neurolysis. Sensory stimulation was elicited at the L3 or L4 vertebral level using a 15 cm insulated radiofrequency needle with a 5-mm active tip. During sensory stimulation, patients described paresthesiae to the ipsilateral buttock and lower extremity. Stimulation intensity was less than 0.8 V at 50 Hz at impedance of 300 Ohms or less. Motor stimulation did not occur up to the maximum voltage tested (2.0 V at 2 Hz) Sensory stimulation of the lumbar sympathetic trunk may be used to aid in localization of the active tip of the radiofrequency needle, in preparation for lesioning. A dermatomal sensory pattern was observed, suggesting that afferent sensory fibers travel in the lumbar sympathetic trunk. The implications of this observation for understanding the mechanism of CRPS-related pain are discussed.