[The spinal somatosensory evoked potentials in amyotrophic lateral sclerosis in relation to the spinal cord conduction velocities].

The lumbar-to-cervical conduction velocity (spinal cord conduction velocity, SCCV) was electrophysiologically studied in 14 patients with amyotrophic lateral sclerosis (ALS). The age of these patients ranged from 37 to 63, averaging 51.0 years old. We recorded the spinal somatosensory evoked potentials (SSEPs) from the surface electrodes at the level of the C2 spine and the T12 spine by the simultaneous stimulation of bilateral posterior tibial nerves. SCCV from the lumbar to cervical was measured from the latency difference between both SSEPs elicited at the each position. As the results, SCCVs were in the range of 50.6-66.6 (58.6 +/- 4.7: mean +/- SD) m/sec in normal age matched controls (18 adult volunteers, 46-63 years old, averaging, 52.7). On the other hand, in ALS patients, SCCVs were in the range of 42.1-67.1 (53.5 +/- 7.8: mean +/- SD) m/sec, values of which were lowered compared to those in normal subjects. These examination documented 4 out of 14 patients with ALS (28.6%) showing abnormalities beyond standard deviation. The vibration sense was checked by using 128 Hz tuning fork at the ankles, and for the quantitative measurement, a newly designed vibriometer being attached the piezoelectric accelerometer to the end of 128 Hz tuning fork was applied in 14 ALS patients. The vibration sense at the ankles was diminished in 6 patients, and 3 patients showed the abnormalities beyond 2 standard deviations. The degree of lowering in SCCVs among ALS patients were correlated with the degree of diminution of impaired vibration sense and the duration of illness, but were not correlated with the H/M ratio and the latency difference between T wave and H wave. Since SSEP impulses are transmitted in dorsal columns and dorsolateral fasciculus predominantly by large diameter and fast-conduction fibers, our results may suggest that, in ALS patients, spinal cord conduction velocities of ascending fibers mediating the dorsal columns and dorsolateral fasciculus are disturbed compared to those in normal subjects, and that the functional disturbance of ascending fibers mediating the dorsal columns and dorsolateral fasciculus plays the important role in the high rates of impaired vibration sense among ALS patients.