Hirayama disease: three cases assessed by F wave, somatosensory and motor evoked potentials and magnetic resonance imaging not supporting flexion myelopathy.

Traumatic chronic injury of the cervical spinal cord caused by neck flexion ("flexion myelopathy") is one of the suggested pathogenetic mechanisms for Hirayama disease (HD). Neurophysiological data, especially reporting particularly N13 cervical somatosensory response, are scarce and conflicting in HD. F wave, somatosensory evoked potentials (SEP), motor evoked potentials (MEP) and magnetic resonance imaging (MRI) studies were assessed in 3 HD male patients (aged 22, 36, and 51 years) with the aim of evaluating the functional effects of neck flexion in HD. Median and ulnar F waves, median, ulnar and posterior tibial SEP, and upper and lower limb MEP were performed bilaterally in standard conditions and during neck flexion in the patients. Cervical spinal MRI study was performed in standard position in two patients and both in standard and flexed positions in the third patient. F wave, SEP, and MEP findings did not show statistically significant differences in standard conditions and during neck flexion both in HD patients and controls. MRI with neck in standard position was normal in two patients, while in the third patient revealed cervical anterior horns signal changes and cord atrophy. In this patient, MRI with the neck in flexion showed that the spinal cord was normally located, was not compressed within the cervical canal and that there were no abnormalities of the dural sac. These findings suggest that in a complex disorder like HD no definite conclusions can be drawn from the present paper and some cases of HD without evidence of "flexion myelopathy" might have a different pathogenetic mechanism.