The cutaneous silent period is preserved in cervical radiculopathy: significance for the diagnosis of cervical myelopathy

Abstract

Electromyographic (EMG) activity from voluntarily contracting hand muscles undergoes transient suppression following nociceptive fingertip stimulation. This suppression is mediated by a spinal inhibitory reflex designated the cutaneous silent period (CSP). The CSP is abolished or altered in a variety of myelopathic conditions. However, before the CSP can gain acceptance as an aid in the diagnosis of myelopathy, the contribution of non-myelopathic conditions that can interrupt the afferent pathways responsible for the CSP needs to be considered. Accordingly, we examined the effect of radiculopathy on the CSP. Nociceptive stimulation was applied to thumb (C6 dermatome), middle (C7) and little (C8) fingers of 23 patients with cervical radiculopathy. Four or more CSP responses were recorded in abductor pollicis brevis muscle following digital stimulation. The patients had C6 (n = 10), C7 (n = 7), or C8 (n = 6) radiculopathy documented by EMG. A complete CSP was elicited in 21 of 23 patients with comparable latencies and durations irrespective of digit stimulated. We conclude that the CSP is preserved in radiculopathy, probably because afferent impulses are carried by smaller, slower conducting 'injury-resistant' A-delta fibers. These results provide important missing evidence that ensures specificity of CSP alterations in the diagnosis of cervical myelopathy. The finding that the CSP is spared in radiculopathy should open the door for investigators and clinicians to adopt this simple spinal inhibitory reflex as a physiologic aid in the diagnosis of spinal cord dysfunction.

Preserved cutaneous silent period in cervical root avulsion

“…Cutaneous SP is preserved in radiculopathy, probably because afferent impulses are carried by smaller, slower conducting "injury-resistant" Adelta fibers. 18 These results provide important missing evidence that ensures specificity of cutaneous SP alterations in the diagnosis of cervical myelopathy. Preserved cutaneous SP in traumatic brachial plexopathy has been already demonstrated.…”

“…These motor fibers are probably also more sensitive to damage than sensory fibers, especially A-delta ones. 18 The diameter and the number of nerve fibers of each nerve root differs in cervical, thoracic and lumbar segments 38 and the better knowledge about preserved nerve fibers continuity provides basic data for future neuroanastomosis. 27 Preserved cutaneous SP proves that spinal cord circuit is functionally intact.…”

“…11,[18][19][20][21] Sensory thresholds following electrical stimulation with constant current square waves of 0.5 ms duration and a stimulation rate of 0.5-0.7 Hz were established for digit I, digit III and digit V in each subject. Subjects were then asked to perform thumb abduction with attempted 25% of their maximum force.…”

“…[11][12][13][14] Absence of radiculopathy, almost normal cutaneous SP has been observed. 18 The CSP technique can quickly determine whether afferent impulses in A-delta fibers pass through individual cervical roots to enter the spinal cord. It is believed that the impulses that originate in the fingertips to produce the CSP ascend along their respective nerves and pass through the corresponding C6, C7 or C8 roots.…”

Inhibition of motoneurons during the cutaneous silent period in the spinal cord of the turtle

“…These parameters of the CSP can be useful as supplementary evaluation of the functional state of peripheral nerves and local spinal sensory motor networks in disease (Leis et al 2011;Onal et al 2010;Oz et al 2011;Svilpauskaite et al 2006).…”