[Small fiber sensory neuropathies: contribution of laser evoked potentials]

Standard neurophysiological techniques evaluate exclusively large myelinated fibers, but are not useful to explore sensory small fibers. Quantitative sensory tests have been developed to explore the thermal nociceptive function but this exploration is only subjective. Laser evoked potentials (LEPs) represent a noninvasive and objective test to explore thermal and nociceptive pathways. The clinical interest of LEPs have been assessed recently in the diagnosis of small fibers sensory neuropathies. In routine, the determination of detection and nociceptive thresholds, the analysis of N2P2 latencies and amplitudes enable demonstration of a dysfunction of A delta nerve fibers, to quantify these lesions and to determine whether the neuropathies are length-dependent or not. The LEP amplitude is negatively correlated to deafferentation. The interest of LEPs remained to be studied compared to skin biopsy.