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Research paper
Sensory axonal dysfunction in cervical radiculopathy
  1. Jia-Ying Sung1,2,
  2. Jowy Tani1,
  3. Kuo-Sheng Hung3,4,
  4. Tai-Ngar Lui3,
  5. Cindy Shin-Yi Lin1,5
  1. 1Department of Neurology, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan
  2. 2Department of Neurology, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan
  3. 3Division of Neurosurgery, Department of Surgery, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan
  4. 4Department of Neurosurgery, Clinical Research Center, Graduate Institute of Injury Prevention and Control, Taipei Medical University, Wan Fang Hospital, Taipei, Taiwan
  5. 5Translational Neuroscience, Department of Physiology, School of Medicine Science, Faculty of Medicine, University of New South Wales, Sydney, Australia
  1. Correspondence to Dr Jia-Ying Sung, Department of Neurology, Taipei Medical University, Wan Fang Hospital, Taipei 116, Taiwan; sung.jiaying{at}gmail.com Associate Professor Cindy Shin-Yi Lin, PhD, Translational Neuroscience, Department of Physiology, School of Medicine Science, Faculty of Medicine, University of New South Wales, Sydney, Australia; c.lin{at}unsw.edu.au

Abstract

Objective The aim of this study was to evaluate changes in sensory axonal excitability in the distal nerve in patients with cervical radiculopathy.

Methods The patients were classified by the findings of cervical MRI into two subgroups: 22 patients with C6/7 root compression and 25 patients with cervical cord and root compression above/at C6/7. Patients were investigated using conventional nerve conduction studies (NCS) and nerve excitability testing. Sensory nerve excitability testing was undertaken with stimulation at the wrist and recording from digit II (dermatome C6/7). The results were compared with healthy controls. Both preoperative and postoperative tests were performed if the patient underwent surgery.

Results Sensory axonal excitability was significantly different in both cohorts compared with healthy controls, including prolonged strength-duration time constant, reduced S2 accommodation, increased threshold electrotonus hyperpolarisation (TEh (90–100 ms)), and increased superexcitability. The changes in these excitability indices are compatible with axonal membrane hyperpolarisation. In five patients who underwent surgery, the postoperative sensory excitability was tested after 1 week, and showed significant changes in TE (TEh (90–100 ms) and TEh slope, p<0.05) between presurgery and postsurgery.

Conclusions The present study demonstrated distal nerve axonal hyperpolarisation in patients with cervical radiculopathy. These findings suggest that the hyperpolarised pattern might be due to Na+-K+ ATPase overactivation induced by proximal ischaemia, or could reflect the remyelinating process. Distal sensory axons were hyperpolarised even though there were no changes in NCS, suggesting that nerve excitability testing may be more sensitive to clinical symptoms than NCS in patients with cervical radiculopathy.

  • Neurophysiology
  • Neurosurgery
  • Electrical Stimulation

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