Effect of neck flexion on F wave, somatosensory evoked potentials, and magnetic resonance imaging in Hirayama disease.

BACKGROUND: Flexion myelopathy is one of the suggested mechanism for Hirayama disease (HD) but simultaneous radiological and neurophysiological evaluation is lacking. This study therefore evaluates the effect of neck flexion in HD using somatosensory evoked potentials (SEPs), F waves, and magnetic resonance imaging (MRI).
METHOD: Eight HD patients and seven matched controls were subjected to median and ulnar F wave (minimal latency, FM ratio, persistence, and chronodispersion), and SEPs evaluating N9, N13, and N20 potentials in neutral and neck flexion. Spinal MRI was carried out in neutral and neck flexion and evaluated for cord atrophy, signal changes, cord compression, posterior epidural tissue, and loss of dural attachment.
RESULTS: The patients were aged 19 to 30 years. Minimal F latency, FM ratio, persistence, and chronodispersion in neutral and neck flexion did not show any change nor was there any change in N13 latency and amplitude on median and ulnar SEPs. The difference in these parameters in neutral and neck flexion were also not significant in HD compared with controls. The change in N13 was also not related to loss of dural attachment and posterior epidural tissue.
CONCLUSION: Neck flexion does not produce significant changes in N13 and F wave parameters and is not related to dynamic MRI changes. The other mechanisms for HD should therefore be explored.