Cold-evoked potentials in clinical practice: A head-to-head contrast with laser-evoked responses.

Background: Innocuous cooling of the skin activates cold-specific Aδ fibres, and hence, the recording of cold-evoked potentials (CEPs) may improve the objective assessment of human thermo-nociceptive function. While the feasibility of CEP recordings in healthy humans has been reported, their reliability and diagnostic use in clinical conditions have not been documented.

Methods: Here, we report the results of CEP recordings in 60 consecutive patients with suspected neuropathic pain, compared with laser-evoked potentials (LEPs) which are the gold standard for thermo-algesic instrumental assessment.

Results: CEP recording was a well-tolerated procedure, with only ~15 min of surplus in exam duration. The reproducibility and signal-to-noise ratio of CEPs were lower than those of LEPs, in particular for distal lower limbs (LLs). While laser responses were interpretable in all patients, CEPs interpretation was inconclusive in 5/60 because of artefacts or lack of response on the unaffected side. Both techniques yielded concordant results in 73% of the patients. In 12 patients, CEPs yielded abnormal values while LEPs remained within normal limits; 3 of these patients had clinical symptoms limited to cold sensations, including cold-heat transformation.

Conclusions: CEPs appear as a useful technique for exploring pain/temperature systems. Advantages are low cost of equipment and innocuity. Disadvantages are low signal-to-noise ratio for LL stimulation, and sensitivity to fatigue/habituation. Joint recording of CEPs and LEPs can increase the sensitivity of neurophysiological techniques to thin fibre- spinothalamic lesions, in particular, when abnormalities of cold perception predominate.

Significance: Recording of cold-evoked potentials is a well-tolerated, inexpensive and easy-to-use procedure that can be helpful in the diagnosis of abnormalities in the thin fibre- spinothalamic pathways. Supplementing LEPs with CEPs allows consolidating the diagnosis and, for some patients suffering from symptoms limited only to cold, CEPs but not LEPs may allow the diagnosis of thin fibre pathology. Optimal CEP recording conditions are important to overcome the low signal-to-noise ratio and habituation phenomena, which are less favourable than with LEPs.