Assessing sensory involvement in lower limb nerve lesions using somatosensory evoked potential techniques

Somatosensory evoked potential (SEP) investigations in 18 patients with lower limb lesions are summarized. Seven patients had problems involving the lateral femoral cutaneous nerve, four the femoral nerve, and seven the sciatic nerve. All lesions were unilateral. SEP techniques were accurate in meralgia paresthetica, and all five patients with demonstrable SEP abnormalities were successfully treated surgically. Delayed recovery of sensory function was shown in two patients with femoral nerve lesions and two patients with sciatic nerve lesions. In patients with sensory symptoms, only an SEP abnormality confined to the nerve distribution provides evidence of a lesion in the sensory pathways and helps to exclude psychologic causes. In a case of peripheral nerve Schwannoma, the presence of a small delay in a case of peripheral SEP supported the preoperative assessment that the tumor was not intrinsic in nature, and this was confirmed at surgery and on subsequent full recovery. The SEP technique allows quantitative assessment of sensory nerve conduction through the peripheral neuron and centripetal pathways.