Test-retest reliability of intra-epidermal electrically evoked potentials in comparison with other modalities and across stimulation intensities.

Intra-epidermal electrically evoked potentials (IEEPs) might represent a promising method for an improved characterization of certain spinal pathologies. Before successful clinical implementation, investigating IEEPs reliability is a prerequisite. This study aimed to assess the test-retest reliability of IEEPs compared to contact heat (CHEPs) and pinprick (PEPs) evoked potentials (Experiment 1) and across different intra-epidermal electrical stimulation (IES) intensities (Experiment 2). Experiment 1 included 26 participants (12f, 25.3 ± 4.6years) and assessed pain-related evoked potentials (PREPs) following contact heat (35-60 °C), pinprick (256 mN), and IES (2 × electrical detection threshold, EDT) to the volar forearm. Experiment 2 included 30 participants (20f, 27.7 ± 3.7years) and assessed IEEPs at four IES intensities (1.5 ×, 2 ×, 4 × EDT, and 0.5 mA). Both experiments assessed test-retest reliability with intraclass correlation coefficients (ICCs) and Bland-Altman analyses for N-latencies, NP-amplitudes, and pain ratings. While IEEPs at 2 × EDT in Experiment 1 showed "excellent" reliability for NP-amplitude, comparable to CHEPs and PEPs, reliability for N-latency and pain ratings ranged from "poor" to "fair". This reliability of IEEP N-latencies and pain ratings improved to "good" and "excellent" by applying higher intensities of IES such as 4 × EDT and 0.5 mA. Given the high reliability of IEEPs at 4 × EDT and 0.5 mA, these intensities may be recommendable for clinical application.