Electrophysiologic diagnosis of cervical OPLL myelopathy using evoked spinal cord potentials

The purpose of this study is to establish the correct diagnosis of the location and extent of intraspinal cord lesions in cases of continuous or mixed-type ossification of the posterior longitudinal ligament and to estimate the postoperative prognosis using evoked spinal cord potentials (ESCP). Twenty-six patients, who underwent surgery from 1985 to 1987 and who have been followed for more than 6 months, were examined using a conductive ESCP, which demonstrates lower extremity, bowel, and bladder function, and a segmental ESCP and dermatome segmental ESCP, which demonstrate upper extremity function. A five-pole recording electrode was placed in the cervical epidural space. The stimulation sites were the thoracic epidural space for conductive ESCP, the median nerve at the elbow for the segmental ESCP, and the finger surface for the dermatome segmental ESCP. In cases in which the ESCP disappeared at the middle of the narrow cervical spinal canal, another stimulating electrode was placed in the cisterna magna, and a descending conductive ESCP was recorded to monitor the upper border of the spinal lesion. New findings, which could not be observed by roentgenograms, myelography, and CT scan, were detectable using this technique.