The diagnostic criteria of benign monomelic amyotrophy.

When we consider the Hirayama disease, a contradiction arises from the point of this criterion. According to De Freitas and Nascimento 4 , when MMA is restricted to the distal aspect of the upper limb, it is known as Hirayama disease. Hirayama disease has been called many different names: MMA, juvenile muscular atrophy of distal upper extremity, juvenile asymmetric segmental spinal muscular atrophy, segmental muscular atrophy of distal upper extremity with juvenile onset, and benign focal amyotrophy 5 . The 17th reference of Yılmaz’s 1 article was reported by Hirayama et al. in 1959 6 . This article is also the first article about the disease now known as Hirayama disease 6 . Therefore, we may conclude that MMA and Hirayama disease are considered as the same disease by authors. On the other hand, the radiological investigations of Hirayama disease proved compressive flattening of the lower cervical cord due to forward displacement of the cervical dural sac and spinal cord induced by neck flexion. According to the Hirayama hypothesis, neck flexion causes tightening of the dura and intramedullary microcirculatory compromise with resultant ischemic nerve cell damage6. Nevertheless, there are some differences between the reported case and Hirayama disease: 1The reported case had weakness on proximal muscles of the right upper extremity and scapula. Hirayama disease is characterized by muscular weakness and wasting in the distal upper extremity (the forearm and hand) 6 . Proximal muscle weakness and atrophy in Hirayama disease are extremely rare7. 2The electromyography (EMG) showed abnormalities suggestive of neurogenic changes in 98.4% of 245 cases with Hirayama disease 8 . However, the EMG of the reported case was normal.