Flexion myelopathy: Hirayama’s syndrome

Abstract

Flexion-induced myelopathy is a rare differential diagnosis in unilateral, sometimes bilateral, juvenile upper limb muscular atrophies innervated by C7–Th1 spinal segments. We report a patient with Hirayama’s syndrome with special emphasis on the radiological findings. We report a 29-year-old German female patient who was admitted to our hospital for the presence of atrophy and weakness of the distal upper extremities. Family history was negative for neuromuscular disorders. Symptoms began insidiously and stabilized after several years. Neurologic examination showed a marked bilateral asymmetric atrophy of intrinsic hand and forearm muscles with sparing of all other muscles, including the bulbar ones. No pyramidal or sensory signs or bladder dysfunction were observed. Results of routine blood analysis including vitamin B12 and of CSF analysis were normal. Neurophysiologic examinations showed bilateral severe chronic neurogenic changes in C7–C8–Th1 myotomes, low ulnar nerve compound muscle action potentials, especially no signs of conduction block, and no somatosensory conduction abnormalities. F-wave analysis of the median and of the ulnar nerve, and somatosensory evoked potentials of the medial, ulnar and tibial nerves showed normal results (Figs. 1, 2 and 3). Routine MRI of the spinal column showed focal hyperintensities in the T2 weighted images in the anterior caudal segments of the cervical spinal cord. MRI in neck flexion revealed forward displacement of the posterior cervical dural sac and flattening of the cervical cord, which was pressed against vertebrae and discs. Axial taping reduced forward displacement. The Hirayama hypothesis (Hirayama et al. [5], original description as juvenile muscular atrophy of distal upper extremity) continues to explain best the disease pathogenesis: neck flexion causes tightening of the dura and intramedullary microcirculatory compromise with resultant nerve cell damage. The age-related factor can most likely be accounted for by a growth imbalance between the vertebral column and the cord/dural elements. Resolution of progression is associated with cessation of body growth, after which the symptoms plateau or modestly improve. Hence, spinal compression appears to be related to forward displacement of the posterior dura during neck flexion, and the overly tight dura results in microcirculatory compromise with damage to anterior horn cells [2, 4, 8]. Furthermore, Taylor and Byrnes [7] showed, that compression of any of the upper four segments of the cervical spinal cord, particularly by extramedullary agents, usually causes early symptoms and signs which suggest dysfunction of the lower part of the cervical enlargement. Wasting of the C8–Th1 innervated muscles of the upper limbs, associated with upper cervical compression, was first described by Oppenheim [6]. MRI in neck flexion is diagnostic in Hirayama’s syndrome. Forward displacement of the posterior dura during neck flexion obviously results in microcirculatory compromise with damage to anterior horn cells. The lower cervical segments are not necessarily the place of F. Weber (&) U. M. Mauer Department of Neurology, Military Hospital Ulm, Oberer Eselsberg 40, 89081 Ulm/Donau, Germany e-mail: Dr.Frank.Weber@t-online.de