Cooling the skin for assessing small-fibre function

In this clinical and neurophysiological study using a novel cold stimulator we aim at investigating whether cold evoked potentials may prove to be a reliable diagnostic tool to assess trigeminal small-fibre function.Using a novel device consisting of micro-Peltier elements, we recorded cold evoked potentials after stimulating the supraorbital and perioral regions and the hand dorsum in 15 healthy participants and in two patients with exemplary facial neuropathic pain conditions. We measured peripheral conduction velocity at the upper arm and studied the brain generators using source analysis. In healthy participants and patients, we also compared cold evoked potentials with laser evoked potentials.In the healthy participants, cold stimulation evoked reproducible scalp potentials, similar to those elicited by laser pulses, though with a latency of about 30 ms longer. The mean peripheral conduction velocity, estimated at the upper arm, was 12.7 m/s. The main waves of the scalp potentials originated from the anterior cingulate gyrus and were preceded by activity in the bilateral opercular regions and bilateral dorso-lateral frontal regions. Unlike laser stimulation, cold stimulation evoked scalp potential of similar amplitude across perioral, supraorbital and hand dorsum stimulation. In patients with facial neuropathic pain, cold evoked potential recording showed the selective damage of cold pathways providing complementary information to laser evoked potential recording.Our clinical and neurophysiological study shows that this new device provides reliable information on trigeminal small-fibres mediating cold sensation, and might be useful for investigating patients with facial neuropathic pain associated with a distinct damage of cold-mediating fibres.