Vestibular Asymmetry as the Cause of Idiopathic Scoliosis: A Possible Answer fromXenopus

Abstract

Human idiopathic scoliosis is characterized by severe deformations of the spine and skeleton. The occurrence of vestibular-related deficits in these patients is well established but it is unclear whether a vestibular pathology is the common cause for the scoliotic syndrome and the gaze/posture deficits or if the latter behavioral deficits are a consequence of the scoliotic deformations. A possible vestibular origin was tested in the frog Xenopus laevis by unilateral removal of the labyrinthine endorgans at larval stages. After metamorphosis into young adult frogs, X-ray images and three-dimensional reconstructed micro-computer tomographic scans of the skeleton showed deformations similar to those of scoliotic patients. The skeletal distortions consisted of a curvature of the spine in the frontal and sagittal plane, a transverse rotation along the body axis and substantial deformations of all vertebrae. In terrestrial vertebrates, the initial postural syndrome after unilateral labyrinthectomy recovers over time and requires body weight-supporting limb proprioceptive information. In an aquatic environment, however, this information is absent. Hence, the lesion-induced asymmetric activity in descending spinal pathways and the resulting asymmetric muscular tonus persists. As a consequence the mostly cartilaginous skeleton of the frog tadpoles progressively deforms. Lack of limb proprioceptive signals in an aquatic environment is thus the element, which links the Xenopus model with human scoliosis because a comparable situation occurs during gestation in utero. A permanently imbalanced activity in descending locomotor/posture control pathways might be the common origin for the observed structural and behavioral deficits in humans as in the different animal models of scoliosis.

Hypothesis on the Pathogenesis of Idiopathic Scoliosis

“…After metamorphosis into young adult frogs, X-ray images and three-dimensional reconstructed micro-computer tomographic scans of the skeleton showed deformations similar to those of scoliotic patients. The skeletal distortions consisted of a curvature of the spine in the frontal and sagittal plane, a transverse rotation along the body axis and substantial deformations of all vertebrae (Lambert et al, 2009). A clinical study from Wiener-Vacher (Wiener-Vacher & Mazda, 1998) supports the hypothesis that central otolith vestibular system disorders lead to a vestibule-spinal system imbalance, and may be a factor in the cause of AIS.…”

Evaluation of motion sickness susceptibility by motion sickness susceptibility questionnaire in adolescents with idiopathic scoliosis: a case–control study

“…In favor of the first theory, investigations in AIS have shown disturbances of the different sensory modalities [5][6][7][8][9]. For example, several authors suggest asymmetrical peripheral disorder of the vestibular system in AIS [6,[9][10][11]. This abnormality could induce, via impaired activity of vestibulo-spinal tract, asymmetric paravertebral muscle tone [9,11].…”

“…For example, several authors suggest asymmetrical peripheral disorder of the vestibular system in AIS [6,[9][10][11]. This abnormality could induce, via impaired activity of vestibulo-spinal tract, asymmetric paravertebral muscle tone [9,11]. This asymmetric recruitment of paraspinous musculature, in growth period, leads to scoliotic deformation [9,11].…”

A new approach to corpus callosum anomalies in idiopathic scoliosis using diffusion tensor magnetic resonance imaging

“…These symptoms suggest that a defect of processing by the central nervous system may contribute in the aetiopathogenesis of IS. Despite the difficulty to identify a causal relationship [8] between these neurological dysfunctions and IS, further characterization of functional and morphological changes in the brain would improve our understanding of the disease.…”