title: Effect of neck flexion on somatosensory and motor evoked potentials in Hirayama disease.
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.
  
  
  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.
  
  
  CONCLUSIONS
  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.
authors: Department of Neurology, Tel-Aviv Sourasky Medical Center, Tel-Aviv, Israel; Sackler Faculty of Medicine, Tel-Aviv University, Tel-Aviv, Israel. Electronic address: alonabmail@gmail.com.
authors: A
authors: A
authors: Abraham
authors: M
authors: M
authors: Gotkine
authors: V E
authors: VE
authors: Drory
authors: S C
authors: SC
authors: Blumen
mesh_terms: D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D004558:Electric Stimulation; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D006801:Humans; D008297:Male; D009333:Neck / Q000502:physiology*; D011712:Pyramidal Tracts / Q000503:physiopathology; D014897:Spinal Muscular Atrophies of Childhood / Q000503:physiopathology*
keywords: Cervical collar; Cervical flexion myelopathy; HD; Hirayama disease; MEP; Microcirculatory disturbances; Motor evoked potentials; SEP; Somatosensory evoked potentials