Cutaneous silent periods of the vastus medialis evoked by the stimulation of lateral femoral cutaneous nerve

Objective Cutaneous silent period (CSP), which is a spinal reflex mediated by A-δ cutaneous afferents, is transient suppression of the electromyographic activity. In this study, our aim is to investigate CSPs of vastus medialis muscle (vm-CSP) evoked by the stimulation of the lateral femoral cutaneous nerve (LFCN) in healthy controls and in patients with meralgia paresthetica (MP). Methods Twenty-one patients with MP (17 unilateral, 4 bilateral) and 27 healthy controls were included. Nerve conduction studies of LFCN and vm-CSP were analyzed in all subjects. A stimulus train consisting of five electrical shocks was applied to the skin at the anterolateral side of the thigh for recording of the vm-CSP. Results Nerve conduction abnormalities of LFCN were observed in all patients with MP. Mean duration of vm-CSP was 69.7±9.2 ms, and mean onset latency was 44.7±6.9 in healthy controls. Onset latency of vm-CSP was significantly prolonged and the duration of vm-CSP was significantly shortened in patients with MP. Vm-CSP abnormalities were observed in 20/25 extremities with MP. Conclusions Dysfunction of A-δ afferents may cause these findings in patients with MP. Additionally, spinal modulation of pain may also play a role in the explanation of our findings. Significance The present study demonstrates the CSP alterations in the patients with entrapment neuropathy of a cutaneous nerve.