Abstract: Objective To investigate the clinical, electrophysiological and magnetic resonance imaging (MRI) characteristics of Hirayama disease. Methods 12 cases with Hirayama Disease were analyzed retrospectively. Results and Conclusion All the patients were male, onset at adolescence, with muscle weakness and atrophy on one or two upper limbs, but without sensory disorder or pyramidal sign. The EMG showed neurogenic abnormalities in the areas dominated by C₇-T₁ nerve in all the patients. Cervical cord MRI found slight atrophy of lower cervical cord in 3 cases in routine position，compressed and displacement forward in flexion position in 12 cases，with posterior epidural space widening，lunular or striped high signal and voids of vessel in some patients. Enhancement scanning in 4 cases showed lunular sign enhanced. Biceps muscles biopsies were performed in 3 cases, the pathology Results appear neuropathic change in 1 cases, another 2 cases were normal.

Key words: Hirayama disease, electromyogram, magnetic resonance imaging