Spinal Dynamics in Monomelic Amyotrophy
August 1, 2000 2 minutes read
Spinal Dynamics in Monomelic Amyotrophy
Abstract & Commentary
Source: Hirayama K, Tokumaru Y. Cervical dural sac and spinal cord in juvenile muscular atrophy of distal upper extremity. Neurology 2000;54:1922-1926.
Seventy-three japanese patients—68 men and five women—with juvenile onset (ages 11 to 19 years) muscular atrophy of the upper extremity (monomelic amyotrophy, MA) were compared to 20 disease-free controls (16 men, 4 women). The goal was to determine what effect, if any, movement of the cervical dural sac and spinal cord during neck flexion contributed to the pathogenesis of MA. All patients had typical clinical features of MA, including an insidious onset of weakness and atrophy in one (n = 59) or both (n = 14) arms. Signs and symptoms initially progressed, but spontaneously arrested after several years. Upper motor neuron, sensory, and sphincteric symptoms and signs remained absent. Diseased control patients suffered from cervical or lumbar spondylosis, spastic paraparesis, spinocerebellar degeneration, vascular malformation, syrinx, and peripheral neuropathy. All subjects underwent radiographic study between the ages of 12 and 52 years, including myelography, postmyelographic computerized tomography, and/or MRI of the cervical spine in full flexion with measurement of the anteroposterior diameter taken in multiple positions. For statistical analysis, younger (< 30 years at myelography) and older groups were separated and compared using student’s t-test.
Striking dynamic changes of the position and diameter of the cervical dural sac on myelography were seen in 64 of 73 (88%) of both younger and older MA patients on neck flexion but not extension. Of 49 patients who underwent postmyelography CT in full neck flexion, 46 (94%) showed tightening and forward movement of the dural sac, with 40 (80%) displaying asymmetrical flattening of the spinal cord, even to boomerang shape, corresponding to the affected limb. MRI findings provided further confirmation of cord dynamics and flattening in 41 of 47 so studied (87%). None expressed any abnormal intrinsic cord signal. No controls showed cord flattening during neck flexion on CT myelography or MRI. MA may result from traumatic cervical myelopathy consequent to the activities of daily living (neck flexion).
Commentary
Blessedly few MA patients come to autopsy, but one such patient demonstrated ischemic changes in C5 to T1 anterior horn cells supporting a vascular etiology (J Neurol Neurosurg Psychiatry 1987;50:285-290). MA has also developed in limbs following trauma and plaster cast immobilization (left elbow sprain and tibial tuberosity fracture in 1 patient each), possibly implying an association with the injury (Muscle Nerve 1997;20:425-430). Focal self-limiting motor neuron disease would be most consistent with the clinical syndrome but, in two brothers, one with amyotrophic lateral sclerosis and one with MA, the former expressed the superoxide dismutase 1 (SOD1) mutation whereas the latter did not (Arch Neurol 1997;54:46-50). Finally, a study of growth curves in seven MA adolescents correlated the age of onset with periods of most rapid height growth and radiographic evidence of disappearance in the slackness of dorsal roots. The phenomenon supports the notion that anatomical factors play a role in MA etiopathogenesis. —michael rubin
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