Effect of Neck Flexion on Somatosensory and Motor Evoked Potentials in Hirayama Disease (P03.169)

Abstract

Objective: Determining the effect of neck flexion on measured SEP and MEP parameters, regarding the hypothesis that Hirayama disease (HD) is a consequence of cervical flexion myelopathy. Background Hirayama disease (HD) develops mainly in young men, characterized by atrophy and weakness of the forearm and hand muscles, in a C7-T1 myotome distribution, usually unilaterally or asymmetrically, followed by spontaneous arrest within several years. The etiology of HD is not well understood. One hypothesis, mainly based on MRI findings, is that HD is a consequence of cervical flexion myelopathy. Concerning this hypothesis, previous neurophysiological and pathological studies produced conflicting findings. Design/Methods: 15 Israeli male patients, mean age 23 ± 6.5 years (range 17-31), with definite HD underwent somatosensory evoked potentials (SEP) and motor evoked potentials (MEP) studies in neutral position and with the neck fully flexed. SEP studies included stimulation of median and ulnar nerves at the wrist, and tibial nerve at the ankle with recording over ipsilateral erb9s point and cervical spine, and contralateral sensory cortex. MEP recordings were obtained by magnetic stimulation of the motor cortex and the cervical spinal cord; the evoked responses were recorded from the contralateral thenar and abductor hallucis muscles. Results: No significant differences were found in SEP studies for the mean values of median and ulnar N9, N13, N20, and tibial P38 latencies and amplitudes in HD patients between neutral and flexed position. MEP studies detected a statistically significant drop in mean upper limb cervical amplitude, and prolongation in lower limb latency during neck flexion compared to the neutral position. Conclusions: In this large cohort of patients neck flexion had no effect on measured SEP parameters, but influenced slightly part of the MEP variables, supporting the view of a negative effect of neck positioning in HD. Disclosure: Dr. Abraham has nothing to disclose. Dr. Gotkine has nothing to disclose. Dr. Drory has nothing to disclose. Dr. Blumen has nothing to disclose.