知覚障害を欠きMRIにて巨大なsyrinxが描出された脊髄空洞症の1例

抄録

Patients with syringomyelia are usually diagnosed by its characteristic symptoms and signs including dissociated sensory loss, muscle weakness and atrophy of hands and arms, pyramidal tract signs in the lower extremities and disturbed autonomic nerve function. It is difficult to diagnose cases lacking in these classical clinical features, especially in those lacking sensory deficit. Recently developed MRI, however, has been reported to reveal the spinal cavitation in abortive cases of syringomyelia. We found a 49 year-old female who showed no sensory disturbance in spite of having a large syrinx demonstrated by MRI.
Her neurological findings were as follows : absent or diminished deep reflexs in the upper extremities and hyperactive reflexes in the lower extremities with positive extensor plantar responses : muscle weakness and atrophy of hands and forearms with occasionally observed fasciculation ; and mild thoracic scoliosis. Sensations to touch, pain and temperature were preserved as well as deep sensation. MRI clearly delineated a large syrinx and swollen spinal cord below the third cervical segment with a narrowed subarachnoid space. Chiari-Arnold type 1 malformation was also demonstrated. Myelography and CT myelography with metrizamide confirmed the MRI findings.
Her neurological findings might have led us to diagnose her as motor neuron disease if the neuroradiological examinations were not performed. Therefore, it should be noted that because the diagnostic importance of sensory loss in syringomyelia is stressed, a patient without definite sensory loss is apt to be misdiagnosed as motor neuron disease. It is essential to differentiate the two disorders, since a shunt operation is known to improve the neurological deficits in syringomyelia while motor neuron disease is still a fatal disorders. For this purpose, our case clearly showed the diagnostic usefulness of MRI.
It is generally accepted that dissociated sensory loss in syringomyelia is caused by disruption of the ventral white commissure distended and compressed by a expanded syrinx. Although the syrinx seemed large enough to damage the commissure in the present case, there was no sensory disturbance. Several authors have recently reported that there is no significant relationship between the neurological deficit and the dimensions of the syrinx. This means that the clinical symptoms and signs are not produced simply by intraspinal tissue being directly damaged by the expanded syrinx. The effects of disturbed circulation secondary to the compression, the difference in sensitivity to the ischemia or the compression, the rate of growth of the syrinx, and the compensatory or reserve capacity of the tissue should be all considered.