F-responses after metrizamide and iohexol lumbar myelography.

We measured several F- and averaged F-response variables before and after lumbar myelography with metrizamide and iohexol in order to evaluate possible effects of these contrast agents upon proximal motor nerve conduction and motor neurone exitability. Averaged F-response onset latency increased while both duration and amplitude decreased after iohexol myelography. These changes were interpreted as signs of minor neural depression but they were slight and without clinical significance in the individual patient. F-response variables were not affected after metrizamide myelography.