Motor cortical hyperexcitability in idiopathic scoliosis: could focal dystonia be a subclinical etiological factor?

Abstract

The aetiology of idiopathic scoliosis (IS) remains unknown; however, there is a growing body of evidence suggesting that the spine deformity could be the expression of a subclinical nervous system disorder. A defective sensory input or an anomalous sensorimotor integration may lead to an abnormal postural tone and therefore the development of a spine deformity. Inhibition of the motor cortico-cortical excitability is abnormal in dystonia. Therefore, the study of cortico-cortical inhibition may shed some insight into the dystonia hypothesis regarding the pathophysiology of IS. Paired pulse transcranial magnetic stimulation was used to study corticocortical inhibition and facilitation in nine adolescents with IS, five teenagers with congenital scoliosis (CS) and eight healthy age-matched controls. The effect of a previous conditioning stimulus (80% intensity of resting motor threshold) on the amplitude of the motor-evoked potential induced by the test stimulus (120% of resting motor threshold) was examined at various interstimulus intervals (ISIs) in both abductor pollicis brevis muscles. The results of healthy adolescents and those with CS showed a marked inhibitory effect of the conditioning stimulus on the response to the test stimulus at interstimulus intervals shorter than 6 ms. These findings do not differ from those reported for normal adults. However, children with IS revealed an abnormally reduced cortico-cortical inhibition at the short ISIs. Cortico-cortical inhibition was practically normal on the side of the scoliotic convexity while it was significantly reduced on the side of the scoliotic concavity. In conclusion, these findings support the hypothesis that a dystonic dysfunction underlies in IS. Asymmetrical cortical hyperexcitability may play an important role in the pathogenesis of IS and represents an objective neurophysiological finding that could be used clinically.

Altered Topological Organization of Cortical Network in Adolescent Girls with Idiopathic Scoliosis

“…In short, increased central role of temporal and occipital cortex and decreased central role of limbic cortex were observed in AIS patients. Furthermore, the altered distribution pattern of hubs in left (NC/AIS: 12/17) and right hemisphere (NC/AIS: 10/9) indicated the hemispheric asymmetry in AIS patients, and this is in line with the previous studies of AIS [3], [35], [36]. In this study, all AIS patients were with right thoracic curves, supporting the findings of hemispheric asymmetry of hub distribution.…”

Electrophysiological and histological changes of paraspinal muscles in adolescent idiopathic scoliosis

“…These observations demonstrate that central nervous system involvement with abnormal sensorimotor integration may underlie the pathogenesis of idiopathic scoliosis [5,10]. Many authors have focused on changes in the electromyographic activity of the paraspinal muscles during the development and progression of the scoliotic curve [11,12] with increased EMG activity on the convex side; however, it is still not clear whether EMG changes reflect only local neurogenic or muscle disturbance.…”

Sensorimotor Integration in Adolescent Idiopathic Scoliosis Patients

“…It suggests that the motor circuit itself is not different. However, significant right/left asymmetry in cortical excitability was characterized by short-latency cortico-cortical inhibition and intra-cortical facilitation after paired pulse stimulation of the motor cortex (Domenech et al, 2010), reflecting a relative decrease in intra-cortical inhibition circuits of the motor cortex. Such dysregulation with hemispheric asymmetry in motor activity modulation of spinal posture at the intra-cortical level could cause or enhance the scoliotic deformity.…”