Late Presentation of Hirayama Disease With "Snake Eye Sign": A Case Report.

Hirayama disease, also called non-progressive juvenile muscular atrophy of distal upper limbs, is a type of cervical myelopathy associated with flexion movements of the neck. It is a type of benign motor neuron disease seen typically in young males in the age group of 15 to 25. The disease has an insidious onset with a stationary stage following a progressive phase. It is also called monomelic amyotrophy with patients usually presenting with insidious onset unilateral upper limb weakness and muscle wasting. A bilateral and asymmetrical presentation can be seen very rarely. A middle-aged male patient presented with bilateral asymmetrical upper limb weakness, muscle wasting involving forearm and hand muscles. Neurological examination showed bilateral upper limb weakness and muscle wasting involving forearm and hand muscles, with a classical pattern of muscle wasting in bilateral forearm muscles called oblique amyotrophy. A clinical diagnosis of Hirayama disease was made and the patient was sent to the radiology department for Magnetic Resonance Imaging of the cervical spine in flexion and neutral positions. The imaging findings were consistent with the clinical diagnosis of Hirayama disease with the presence of an abnormal "snake eye appearance". The electrophysiological assessment done including the electromyography and nerve conduction studies were also consistent with the clinical diagnosis. "Snake eye appearance" on MRI in patients with Hirayama disease is associated with unfavorable outcomes and represents cervical myelopathy involving the anterior horn cells.