Objective
The purposes of this study were to evaluate the diagnostic value of dermatomal somatosensory evoked potentials (DSEPs) in the unilevel/unilateral lumbosacral radiculopathies.

Method
The study was performed on 41 patients with herniated lumbosacral disc which was confirmed by magnetic resonance imaging, and the patients with clinical lumbosacral radiculopathies (L5 radiculopathy in 33 cases and S1 radiculopathy in 8 cases). Stimulation sites were over the dorsum of the foot on the distal fifth metatarsal bone for the S1 dermatome and at the interdigital web space between first and second toe for the L5 dermatome. Recordings were made at Cz' and reference to Fz. Conventional nerve conduction study, needle EMG and H-reflex were also examined.

Results
While the needle EMG showed abnormalities in 32 patients (78.0%), the abnormalities of DSEPs were in 13 patients (31.7%): 33.3% for the L5 radiculopathy and 25.0% for the S1 radiculopathy, respectively. Moreover, there was no significant relationship between the abnormal findings of needle EMG and DSEPs (p＞0.05). The H-reflexes were abnormal in 6 of 7 patients (85.7%). And then two of them were found abnormal in S1 DSEPs.

Conclusion
The conventional needle EMG appears to be the more useful electrophysiological technique in the diagnosis of lumbosacral radiculopathies. The ultimate diagnostic value of DSEPs in lumbosacral radiculopathies is doubtful and controversial.