Focal paresthesias with cervical magnetic stimulation

Subjects undergoing cervical magnetic stimulation with an appropriate coil report focal hand paresthesias in a dermatomal distribution, but the physiologic accuracy of such subjective experiences has been uncertain. In six subjects, we used a butterfly-shaped magnetic coil to stimulate positions on the back of the neck at 1-cm intervals, constant output, and random order, while the subject-estimated location and intensity of paresthesias and sensory nerve action potentials (SNAPs) were recorded from the thumb or index finger. Three subjects each also had recording of finger accelerometry or compound motor action potentials (CMAPs) in the hand and forearm. We found a consistent correlation between subjective paresthesias and SNAPs but an appropriate anatomic divergence between paresthesias and accelerometry or CMAPs. Focal paresthesias from cervical magnetic stimulation are reliable and anatomically accurate, strengthening the hypothesis that other magnetic sensory phenomena are valid as well.