Cold evoked potentials: Acquisition from cervical dermatomes

Abstract

Introduction: Cold evoked potentials (CEPs) represent a novel technique to assess the integrity of cold-specific pathways within the somatosensory system. So far an objective assessment of these pathways has not been implemented into the clinical routine. Specifically, CEPs may help to elucidate the pathophysiological underpinnings of altered cold processing in neurological diseases.

Objective: To test feasibility and test-retest reliability of CEPs within two cervical dermatomes, including recording sites in glabrous and hairy skin, in order to facilitate the transition into clinical practice.

Methods: Twenty healthy subjects received 15 cold stimuli applied by a thermode either at the hand dorsum (C6 dermatome, hairy skin), the shoulder (C4 dermatome, hairy skin) or the thenar eminence (C6 dermatome, glabrous skin). Stimuli were applied from a baseline temperature of 30°C down to a destination temperature of 25°C at a rate of 20°C/s. N2 latencies and N2P2 amplitudes were recorded at the vertex using a surface electroencephalogram and test-retest statistics were calculated.

Results: Slight, innocuous cooling (Δ5°C) from a baseline temperature of 30°C elicited a brief percept of cooling and generated a vertex potential (N2P2) in most subjects. The latency of the vertex response is consistent with A-delta fiber activation. Based on test-retest analyses (i.e., intraclass correlation coefficients (ICCs) and Bland-Altman analyses) reliability is best within the C4 dermatome and for stimulation of hairy skin. ICCs display fair to substantial (ICCs from 0.51-0.81) reliability for amplitudes across all stimulation sites, possibly due to floor effects. CEPs latencies, however, were only poorly reliable (ICCs from -0.13 to 0.31).

Conclusion: The acquisition of CEPs from cervical dermatomes is feasible. Since involvement of cold-specific pathways is relevant for several pathologies in clinical neurology, the application of CEPs may complement existing techniques like contact heat and laser stimulation in the assessment of peripheral and central nervous system disorders. Future studies employing different stimulation paradigms using faster cooling are warranted in order to improve the signal-to-noise ratio.

Keywords: A-delta fiber; Cold evoked potential; Cooling; Feasibility; Reliability; Spinothalamic tract.