Abstract
Purpose/ObjectivesWe observed a number of patients who developed Lhermitte’s sign (LS) following radiation to the head and neck (H/N), since instituting volumetric modulated arc therapy (VMAT). We aimed to investigate the incidence of LS following VMAT-based RT without chemotherapy, and determine the dosimetric parameters that predict its development. We explored whether the role of inhomogeneous dose distribution across the spinal cord, causing a “bath-and-shower” effect, explains this finding.Methods and MaterialsFrom 1/20/2010–12/9/2013, we identified 33 consecutive patients receiving adjuvant RT using VMAT to the H/N without chemotherapy at our institution. Patients’ treatment plans were analyzed for dosimetric parameters, including dose gradients along the anterior, posterior, right, and left quadrants at each cervical spine level. Institutional Review Board approval was obtained.Results5 out of 33 (15.2%) patients developed LS in our patient group, all of whom had RT to the ipsilateral neck only. LS patients had a steeper dose gradient between left and right quadrants across all cervical spine levels (repeated-measures ANOVA, p = 0.030). Within the unilateral treatment group, LS patients received a higher mean dose across all seven cervical spinal levels (repeated-measures ANOVA, p = 0.046). Dose gradients in the anterior-posterior direction and mean doses to the cord were not significant between LS and non-LS patients.ConclusionsDose gradients along the axial plane of the spinal cord may contribute to LS development; however, a threshold dose within the high dose region of the cord may still be required. This is the first clinical study to suggest that inhomogeneous dose distributions in the cord may be relevant in humans. Further investigation is warranted to determine treatment-planning parameters associated with development of LS.
Highlights
Lhermitte’s sign (LS), a sensation of electrical shock with neck flexion or movement, is a transient phenomenon that correlates with demyelination of the white matter in the spinal cord
Within the unilateral treatment group, LS patients received a higher mean dose across all seven cervical spinal levels
Dose gradients along the axial plane of the spinal cord may contribute to LS development; a threshold dose within the high dose region of the cord may still be required
Summary
Lhermitte’s sign (LS), a sensation of electrical shock with neck flexion or movement, is a transient phenomenon that correlates with demyelination of the white matter in the spinal cord. Previous studies have reported the incidence of LS following conventional radiation therapy or IMRT, with and without chemotherapy, to the head and neck region ranges 3–13% [1, 7,8,9]. Many chemotherapy agents, such as carboplatin, cytarabine, and others are radiosensitizers and can cause peripheral neuropathies; it is conceivable that radiation exposure in the spinal cord makes the blood-brain barrier more vulnerable to the neurotoxic effects of chemotherapy in the spinal cord. There is currently no data to suggest that surgery to the head and neck region increases the incidence
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