P248 Laser evoked cutaneous silent periods in diagnosis of chemotherapy induced small fiber neuropathy

Abstract

Objectives Laser evoked potentials (LEPs) have shown less sensitive results than other tests (e.g., skin biopsies, quantitative sensory testing) in diagnosing small fiber neuropathy (SFN), probably because both central and peripheral nociceptive pathways are assessed. Alternatively, laser evoked cutaneous silent period (Ls-CSP) could selectively evaluate peripheral nociceptive pathways only. Methods Thirty patients with chemotherapy-induced chronic pain and/or dysesthesia were compared with 27 healthy subjects. LEPs were recorded from scalp and Ls-CSPs from the abductor pollicis brevis (APB) muscle following random Neodymium-doped yttrium aluminum perovskite (Nd:YAP) laser stimuli given on hairy skin of the extremities. Results For LEPs, mean values of N1 amplitude in upper extremities (8.6 ± 5.4 vs 12.7 ± 5.2 μ V) and N2P2-amplitudes in upper ( 27.9 ± 17.0 vs 35.8 ± 9.6 μ V) and lower extremities (14.5 ± 11.2 vs 24.4 ± 7.7 μ V) were significantly lower in patients than controls ( p 0.01 ). Ls-CSPs were not reproducible in lower extremities. In 18 patients, Ls-CSPs from APB muscle were not recorded. In the rest of the patients ( n = 12), Ls-CSP latencies (139.9 ± 12.4 vs. 131.9 ± 13.7 ms) and durations (19.8 ± 1.4 vs 18.5 ± 1.3 ms) were not different from controls ( p > 0.05 ). Overall, LEPs and Ls-CSPs were abnormal in 16 (53.3%) and 19 (63.3%) patients, respectively. Discussion Ls-CSPs in upper extremities defined more patients than LEPs in upper and lower extremities. Conclusions Ls-CSPs in hands were more sensitive than LEPs in detecting patients with SFN. Significance Ls-CSP could be a useful supplementary test in the diagnosis of SFN, especially in cases with subtle LEP changes.