O5 Cutaneous silent period recordings and silent period ratio could be used to assess peripheral Aδ functions

Objective Nerve conduction studies have limited diagnostic power to assess A δ and C fibers in patients with mixed (large and small fibre neuropathy together) neuropathy, and no power to diagnose small fiber neuropathy (SFN). An option to assess small fibers using standard electro-diagnostic equipment could be cutaneous silent period (CSP) recordings. Methods Thirty patients with chronic pain and/or dysesthesia due to chemotherapy were compared with 27 healthy subjects. Electrical stimulation (25 mA × 1 ms) was delivered on median-sensory and sural nerves. CSPs were recorded from abductor pollicis brevis (APB) and anterior tibial (TA) muscles. In addition, a derived parameter, silent period ratio (SPR), was used to assess A δ functions. The yields of the tests were compared with laser evoked potentials (LEPs) from upper and lower extremities. Results Latencies of APB-CSP and TA-CSP were not significantly different (p > 0.05) between groups. On the other hand, mean APB-CSP duration was longer (32.5 ± 12.6 vs 27.4 ± 9.2 ms, p = 0.004), mean TA-CSP duration shorter (11.8 ± 12.7 vs 39.9 ± 11.6 ms, p Discussion CSP and SPR revealed comparable results with LEPs (16 patients, 53.3%) to define the patients with SFN. Conclusions CSP and SPR could be used to assess peripheral A δ functions. Significance CSPs could be an option to diagnose SFN in the laboratories having only standard electro-diagnostic equipment.