Objective
To evaluate the diagnostic values of segmental somatosensory evoked potentials (SEPs) in the unilevel/unilateral lumbosacral radiculopathies.

Method
Thirty-nine radiculopathy patients of whom diagnosis was confirmed by the surgery or selective nerve root injection and 20 subjects with no evidence of radiculopathy were included in the study. Before the treatment, superficial peroneal nerve segmental SEPs and sural nerve segmental SEPs were performed. Sensitivities and specificities were delineated from the several diagnostic criteria.

Results
The analysis of side-to-side mean cortical P1 latency difference (＞2.0 SD) reveals a segmental SEPs sensitivity for L5 radiculopathies of 12.1% and sensitivity for S1 radiculopathies of 0%. The analysis of side-to-side mean percent amplitude difference (2.0 SD) reveals a segmental SEPs sensitivity for L5 radiculopathies of 9.1% and sensitivity for S1 radiculopathies of 0%. The analysis of side-to-side mean cortical P1 latency difference (＞3 ms) and the side-to-side mean amplitude reduction (＞50%) show the similar results. The specificities of L5 radiculopathies and S1 radiculopathies are variable from 40.0% to 93.3%. Sensitivities of segmental SEPs are lower than needle EMG. It is not root specific, even the SEP is not obtainable unilaterally.

Conclusion
The diagnostic values of segmental somatosensory SEPs are questionable in the unilevel/unilateral lumbosacral radiculopathies which are confirmed by the surgery or selective nerve root injection.