[Somatotopic Representation of the Anterior Horn within Cervical Enlargement: Reappraisal of Known Doctrine Based on Clinicopathological Findings Seen in Hirayama Disease].

Clinical features (weakness and amyotrophy of intrinsic hand muscles and obliquely distributed amyotrophy of forearm muscles, figure 1), needle electromyographic findings (distribution of neurogenic activities, figure 2), and pathological findings (ischemic necroses of the anterior horns between C6 and T1, figure 3) of Hirayama disease suggest that understanding of somatotopic representation of the anterior horn innervating arm muscles in the cervical enlargement of spinal cord differs from the known doctrine. Anterior horn cells of the intrinsic hand muscles are located between C7 and T1, those of forearm muscles and triceps brachii muscle as elbow extensor are, contrary to the known doctrine, located in C5 and C6, and those of elbow flexors such as biceps brachii and brachioradialis are located in C4 and above (figure 5). Development of dexterity in human hand may reflect development of cervical enlargement in accord with larger areas representing the hand and fingers on cerebral motor cortex.