Correlation between curve severity, somatosensory evoked potentials, and magnetic resonance imaging in adolescent idiopathic scoliosis

Study Design. A prospective study in patients with adolescent idiopathic sc oliosis of different clinical severity using whole-spine magnetic resonance imaging and somatosensory evoked potentials. Objectives. To correlate the presence of magnetic resonance imaging structu ral abnormalities with somatosensory evoked potential-detected functional d isorders in the hind brain and spinal cord and the Cobb's angle in patients with adolescent idiopathic scoliosis and to compare the result with those in healthy matched control subjects. Summary of Background Data. Many different types of neurologic dysfunction have been reported in scoliosis. With the advent of magnetic resonance imag ing, there are increased reports on the association of idiopathic scoliosis and syringomyelia, Chiari I malformation, or tonsillar ectopia. The actual link between structural and functional disorder in idiopathic scoliosis is , however, unclear. Methods. Posterior tibial nerve evoked potentials and whole-spine magnetic resonance imaging were performed in 36 healthy control subjects, 135 patien ts with adolescent idiopathic scoliosis with Cobb's angle less than 45 degr ees, and 29 patients with Cobb's angle more than 45 degrees. Results. Tonsillar ectopia or syringomyelia, detected by magnetic resonance imaging, or functional disturbance in the somatosensory pathway, detected by somatosensory evoked potentials, was found to be significantly more freq uent in the group of patients with severe scoliosis curvature, with an inci dence of 31% and 27.6%, respectively. Incidence of tonsillar ectopia was 33 .3% in patients with abnormal somatosensory evoked potentials in contrast t o the much lower incidence of 2.9% in patients with normal somatosensory ev oked potentials. There was a significant structural and functional link. Th e incidence of syringomyelia in patients with and without tonsillar ectopia was 33.3% and 0.7%, respectively. Conclusions. In patients with adolescent idiopathic scoliosis with severe c urve, the significant association with tonsillar ectopia and abnormal somat osensory function points to a neural origin, Disorders in the somatosensory function may be one of the mechanisms linking tonsillar ectopia to scolios is. Somatosensory evoked potentials and magnetic resonance imaging may have important diagnostic and predictive value and may help in the management o f adolescent idiopathic scoliosis.