Posterior Tibial Somatosensory Evoked Potentials (PTSEPs) in Thoracic Myelopathy

ABSTRACT

The authors perforrned the posterior tibial somatosensory evoked potentials(PTSEP) on 37 patients who had typical symptoms and signs of thoracic myelopathy to evaluat the value of the PTSEP in diagnosing and differentiating among the thoracic lesions The result showed the abnormal PTSEP features which were suggestive of thoraci myelopathy in 33 of 37(89.2%). The most frequent abnormalities were the prolonged central conduction(59.5%), which were either the only one(40.6%) or combined with poor wave formation (18.9%). The second comrnon abnorrnal PTSEP findings were the decreased P1 amplitude relative to TN1 amplitude with hanng nonnal value of TN1-P1 interwave latencies (29.7%). When we divided those 37 subjects into the demyelinating (N =19) and the non-demyelinating group(N=18), the prolonged TN1-P1 interwave latencies were more prominent in the demyelinating(68.4%) than in the non-demyelinating group (50.0%). In contrast, the only relative reduction of P1 amplitude with normal central conduction was more marked in the non-demyelinating(38.9%) than in the demyelinating group(21.1%). However, both of them did not show statistical significances (p<0.254, p<0.235, respectively). The PTSEP methods were found superior to spine MRI in sensitivity in the demyeli nating group, as the PTSEP revealed abnormal findings in 12 subjects with normaI spine MRI. Therefor it is concluded that the PTSEP studies would be helpful in diagnosing the thoracic lesions, especially in patients with the demyelinating lesions. However. Those pararnmters of the prolonged central conduction(TNl-P1) or the relative amplitude redu ction of cortical patentials(P1) were not significant in differentiating the demyelinating from the non-demyelinating lesions.