A 23-year-old man complained of weakness of the right arm that he first noted six years prior to his visit. Neurological examination revealed atrophy and weakness of the triceps and serratus anterior muscle on the right side, which resulted in scapular winging on that side. MRI with neck flexion revealed compression of the cervical cord enabling a diagnosis of flexion myelopathy. Proximal muscle weakness and atrophy in flexion myelopathies including Hirayama disease are extremely rare. Here, we report a case of unilateral, proximal upper limb atrophy with scapular winging, attributed to middle cervical flexion myelopathy.