Abstract
Hirayama disease (HD) is a rare motor disorder mainly affecting young men, characterized
by atrophy and weakness of forearm and hand muscles corresponding to a C7–T1 myotome
distribution. The weakness is usually unilateral or asymmetric and progression usually
stops within several years. The etiology of HD is not well understood. One hypothesis,
mainly based on MRI findings, is that the weakness is a consequence of cervical flexion
myelopathy. The aim of this study was to explore the function of corticospinal and
ascending somatosensory pathways during neck flexion using evoked responses.
Materials and methods
15 men with HD and 7 age-matched control male subjects underwent somatosensory evoked
potentials (SSEP) and motor evoked potentials (MEP) studies with the neck in neutral
position and fully flexed. SSEP studies included electrical stimulation of median
and ulnar nerves at the wrist, and tibial nerve at the ankle with recording over the
ipsilateral Erb's point, cervical spine, and contralateral sensory cortex. MEP recordings
were obtained by magnetic stimulation of the motor cortex and the cervical lower spinal
roots; the evoked responses were recorded from the contralateral thenar and abductor
hallucis muscles.
Results
MEP recordings demonstrated significant lower amplitudes, and slightly prolonged latencies
in HD patients on cervical stimulation, compared to control subjects. During neck
flexion, MEP studies also demonstrated a statistically significant drop in mean upper
limb amplitude on cervical stimulation in HD patients, as well as in control subjects,
although to a lesser degree. In contrast, no significant differences were found in
SSEP studies in HD patients compared to control subjects, or between neutral and flexed
position in these groups.
Conclusion
The study shows a negative effect of cervical flexion on MEP amplitudes in HD patients
as well as in control subjects, requiring more studies to investigate its significance.
Neck flexion did not have an influence on any SSEP parameters in patients or controls.
Abbreviations:
HD (Hirayama disease), MEP (Motor evoked potentials), SEP (Somatosensory evoked potentials)Keywords
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Article info
Publication history
Published online: August 19, 2013
Accepted:
July 30,
2013
Received in revised form:
July 27,
2013
Received:
March 7,
2013
Identification
Copyright
© 2013 Elsevier B.V. Published by Elsevier Inc. All rights reserved.
