Monomelic amyotrophy (MA) is a rare benign lower motor neuron disorder characterized by muscular weakness and wasting in the distal upper extremities during adolescence followed by a spontaneous halt in progression and a stabilization of symptoms. The disease is MONDO_0011224 (monomelic amyotrophy). Also known as: Hirayama disease, JMADUE, benign focal amyotrophy, juvenile muscular atrophy of distal upper extremity, juvenile muscular atrophy of the distal upper limb.