Normative data for the segmental acquisition of contact heat evoked potentials in cervical dermatomes

Abstract

Contact heat evoked potentials (CHEPs) represent a neurophysiological approach to assess conduction in the spinothalamic tract. The aim of this study was to establish normative values of CHEPs acquired from cervical dermatomes (C4, C6, C8) and examine the potential confounds of age, sex, and height. 101 (49 male) healthy subjects of three different age groups (18-40, 41-60, and 61-80 years) were recruited. Normal (NB, 35-52 °C) followed by increased (IB, 42-52 °C) baseline stimulation protocols were employed to record CHEPs. Multi-variate linear models were used to investigate the effect of age, sex, and height on the CHEPs parameters (i.e., N2 latency, N2P2 amplitude, rating of perceived intensity). Compared to NB, IB stimulation reduced latency jitter within subjects, yielding larger N2P2 amplitudes, and decreased inter-subject N2 latency variability. Age was associated with reduced N2P2 amplitude and prolonged N2 latency. After controlling for height, male subjects had significantly longer N2 latencies than females during IB stimulation. The study provides normative CHEPs data in a large cohort of healthy subjects from segmentally examined cervical dermatomes. Age and sex were identified as important factors contributing to N2 latency and N2P2 amplitude. The normative data will improve the diagnosis of spinal cord pathologies.

Figure 1. Study design.

Prior to the recording of contact heat evoked potentials (CHEPs), all participants completed the pain catastrophizing questionnaire followed by pin prick and light touch testing. CHEPs were recorded from dermatomes C4, C6, and C8 (in a randomized order) employing normal followed by increased baseline stimulation.

Figure 2. Representative example of CHEPs of each dermatome and both stimulation protocols.

Figure 3. Summary of latencies and amplitudes for each dermatome and both stimulation modalities.

Increased baseline resulted in (A) increased N2P2 amplitudes and (B) decreased N2 latencies across all dermatomes and age groups. The inter-subject variability of N2 can be minimized by employing increased baseline stimulation.

Figure 4. Pearson correlations between CHEPs parameter and demographics for each dermatome and stimulation protocol.