54. Cutaneous silent period in brachial plexus injury

Abstract

Objectives The cutaneous silent period (CSP) is a spinal inhibitory reflex mediated primarily by small-diameter A-delta fibers, which enter the spinal dorsal horn and suppress activity in spinal motor nuclei in neighboring myotomes. The aim of the study was to define if CSP testing may be particularly useful in evaluation of brachial plexus injury, especially contributing to diagnosis of root avulsion. Methods In 11 patients with traumatic brachial plexus injury (8 males, age 18–62 years) we performed clinical examination, myelo CT and neurophysiological testing. Needle EMG was obtained from the main root muscles of C5–C8 myotomes. CSP was recorded by painful stimuli while the subject maintains a moderately strong voluntary muscle contraction and impulses were delivered to thumb (C6 dermatome), middle (C7) and little (C8) fingers. Results Clinical and EMG examination proved motor root damage of C5 in 3 subjects, C5 and C6 in 3 subjects, C5–C7 in 3 subjects, C5–C8 in 2 subjects. The CSP was partially absent in 3 subjects, however, well preserved in 8 subjects. Conclusion in theory, CSP can be used to quickly monitor afferent impulses travelling through damaged cervical roots, however, in brachial plexus avulsion CSP abnormalities were found only in a few cases. CSP is a robust protective plurisegmental spinal reflex, which is maintained even with a preservation of minimal functional afferent fibers and/or because the afferent signal is amplified within the spinal cord. Supported by Research Projects of Charles University PRVOUK P34, Grant Project of Czech Ministry of Health NT12282, NT13693.