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Somatosensory evoked potential study in cervical radiation myelopathy.

BACKGROUND
To correlate the findings of median nerves somatosensory evoked potentials (SEPs) with clinical manifestations and magnetic resonance (MR) findings in cervical radiation myelopathy after therapeutic irradiation for nasopharyngeal carcinoma.


METHODS
Median nerve somatosensory evoked potentials (SEPs) were recorded in 10 patients with cervical radiation myelopathy. Seven patients were studied by SEP once, two patients received SEP twice, and one patient, three times.


RESULTS
On the basis of the median nerve SEP findings, three groups were identified: Group I, normal SEP responses (N9, N13 and N20); Group II, normal N13 with abnormal N20; Group III, Normal or abnormal N9 with both abnormal N13 and N20.


CONCLUSIONS
The size, eccentricity and extension to the dorsal columns of the lesions correlated well with SEP findings. When the lesions were confined mainly to the lateral column without much involvement of the dorsal columns, SEP findings were normal; with more extensive lesions involving the dorsal columns, SEPs became abnormal.