Hirayama disease is a rare, lower cervical myelopathy affecting young adults. It is responsible for pure distal motor impairment of the upper limbs, with slow progressive development in the metameric territories of C7 to T1. It is thought to be caused by movements involved in flexing the neck. Neutral position magnetic resonance imaging (MRI) looks for abnormal cervical curvature, atrophy with flattening of the cervical spine, anterior cord hyperintensity and especially a lack of posterior apposition of the dural sac. If the condition is suspected, an MRI in flexion should be performed to show anterior displacement of the cord and dural sac, enlargement of the posterior epidural space, an increase in flattening of the cord and congestion of the epidural veins. These dynamic abnormalities tend to disappear after evolving for 10 years. We report two confirmed cases and a probable case of Hirayama disease and discuss its physiopathology.