A 32-year-old man was admitted to our hospital with 1-year history of left forearm and hand weakness and cold intolerance complaint. The patient stated that his complaints had been gradually increasing within the last 6 months. Physical examination showed atrophy in the left hand and forearm muscles, and weakness of this muscle groups was detected on neurologic examination (Fig. 1). Chronic focal anterior horn cell involvement in the left C7–T1 was found on electromyography evaluation. Non-flexion sagittal T2-weighted magnetic resonance imaging (MRI) showed atrophy of the spinal cord at the level of the C6 vertebra (Fig. 2). Non-flexion axial T2-weighted MRI showed focal increased signal in the right side of the spinal cord at the C6 level and atrophy in the left anterior side (Fig. 3). Then, flexion cervical MRI showed anterior shift in the posterior dura mater (Fig. 4). The patient was diagnosed with Hirayama disease as a result of the presence of the characteristic MRI findings. Hirayama disease is characterized by insidious onset of weakness and wasting of the distal upper extremities. It is a rare disease also known as monomelic amyotrophy [ [1] Vargas M.C. Castillo M. Magnetic resonance imaging in Hirayama disease case report. J Radiol Case Rep. 2011; 5: 17-23 Crossref PubMed Scopus (13) Google Scholar ]. When diagnosed early, the use of neck fitting collar and restriction of flexion movements may prevent disease progression. Therefore, clinicians and radiologists should be vigilant toward this disease. Fig. 2Non-flexion sagittal T2-weighted magnetic resonance imaging (MRI) shows atrophy of the spinal cord at the level of the C6 vertebra. View Large Image Figure Viewer Download Hi-res image Fig. 3Non-flexion axial T2-weighted magnetic resonance imaging (MRI) shows focal signal increase in the right side of the spinal cord and atrophy in the left anterior side. View Large Image Figure Viewer Download Hi-res image Fig. 4Flexion sagittal T2-weighted images show two anterior shifting of the posterior wall of the dura mater. The posterior epidural space enlarges with flexion. View Large Image Figure Viewer Download Hi-res image