Evoked potentials in acute transverse myelopathy.

Evoked potential studies were undertaken in nine patients with acute transverse myelopathy three to 25 weeks after onset. The visual evoked potentials (VEP), brain stem auditory evoked potentials (BAEP) or somato-sensory evoked potentials (SEP) after median nerve stimulation were normal in all but one with prolonged latency of VEP. The SEP after tibial nerve stimulation was abnormal in six patients--in three, there was no cortical potential from either side (total conduction block); in two, there was a block on one side and a slightly delayed latency on the other; and in one patient there was a slightly prolonged latency bilaterally. The degree of abnormality was related to the severity of the disease. The recovery was poor in four of five patients with a conduction block and good in three of four patients with a normal or slightly delayed SEP after tibial nerve stimulation. The findings are attributed to oedema and necrosis in the central nervous system, whereas demyelination probably plays a minor role in acute transverse myelopathy.