[New approach for diagnosis and postoperative evaluation in herniated lumbosacral disc].

Dermatomally activated somatosensory evoked potentials (DSSEP's) were recorded over the scalp in 50 healthy subjects and 40 patients who later underwent exploration for herniated lumbosacral discs. The control subjects showed three negative peaks, N40, N56 and N78, and N41, N59 and N82 after bilateral stimulation of L5 and S1 dermatomes, respectively. In the patient group, the first two peaks were often abnormal in the presence of clinical sensory deficit, whereas the third peak tended to remain normal. At surgery, herniated disc was confirmed in all but six patients. The findings in myelogram were misleading in eight patients, showing either false positive or false negative results. The DSSEP's were normal in seven patients with documented disc protrusion at the level of L5 or S1 root. The test was also normal in another case with herniation at the level of S2 root. In this series, DSSEP's was extremely accurate in defining the level and the degree of lumbosacral root involvement. The findings on electrophysiology and myelography are not comparable, but are complementary, the former indicating function and the latter structure. Thus, electrophysiologic studies and myelography were complementary in providing an accurate diagnosis for herniated lumbosacral disc.