Test-Retest Reliability of Perception Threshold Estimation in Small Cutaneous Nerve Fibers: A Methodological Investigation.

Introduction/aims: Nerve excitability testing of small cutaneous nerve fibers has been proposed as a new tool for investigating the underlying mechanisms of small fiber neuropathy. These assessments may be performed using perception threshold tracking with pin-electrodes that preferentially activate small cutaneous nerve fibers. In this study, the test-retest reliability of two perception threshold (PT) algorithms: the Psi method and the Method of Limits (MoL), was compared.

Method: Twenty healthy subjects completed the study. Electrical stimulation was applied using a pin electrode, and the PT to a 1 ms rectangular pulse was estimated six times during two sessions separated by 1 week. The test-retest reliability was evaluated by the intraclass correlation coefficient (ICC) and the coefficient of variation (CV). The two PT algorithms were compared by limits of agreement (LoA).

Results: The ICC indicated better within-session reliability (Psi: 0.77 and MoL: 0.81) than between-session reliability (Psi: 0.58 and MoL: 0.50) regardless of the algorithm used. The PTs were significantly lower when measured with the MoL (0.88 mA) compared to the estimates by the Psi (1.12 mA) method.

Discussion: The estimation of PT can be reliably assessed, especially within-session, with both the MoL and Psi methods. This allows for PT tracking, where PTs to different electrical stimulation provide an estimation of nerve fiber excitability. PT values obtained using different methods are not directly comparable.