Interside comparison of cutaneous silent periods in thenar muscles of healthy male and female subjects

Objective: The cutaneous silent period (CSP) is a spinal inhibitory reflex mediated by A-δ fibers. To date, no data are available about normal interside differences. Methods: Twenty healthy subjects underwent comparison of CSPs in the dominant and non-dominant hand. Surface electromyographic (EMG) recordings were obtained from thenar muscles on either side following ipsilateral recurrent nociceptive digit II stimulation. Results: Group average CSP onset and end latency, CSP duration, and the magnitude of EMG suppression were not significantly different between both sides. Regression analysis revealed powerful correlations between individual CSP parameters of dominant and non-dominant hands. Calculated upper normal limits of maximum interside differences were 17% for CSP onset latency, 14% for CSP end latency, 22% for CSP duration, and 45% for the index of suppression. CSP parameters in right-handed subjects did not differ significantly from those in left-handed subjects. Female subjects tended to have shorter CSP onset latencies, longer CSP duration, and a smaller index of suppression, resulting in a larger overall suppression. Conclusions: CSPs prove to be robust nociceptive cutaneomuscular reflexes with little side-to-side difference. Significance: The presented normative values of interside differences enable a more thorough comparison with patient data in various conditions.