ObjectiveTo determine whether different phenotypes of cervical dystonia (CD) express different types and levels of somatosensory impairment.MethodsWe assessed somatosensory function in patients with CD with and without tremor (n = 12 each) and in healthy age-matched controls (n = 22) by measuring tactile temporal discrimination thresholds of the nondystonic forearm and proprioceptive acuity in both the dystonic (head/neck) and nondystonic body segments (forearm/hand) using a joint position-matching task. The head or the wrist was passively displaced along different axes to distinct joint positions by the experimenter or through a robotic exoskeleton. Participants actively reproduced the experienced joint position, and the absolute joint position-matching error between the target and the reproduced positions served as a marker of proprioceptive acuity.ResultsTactile temporal discrimination thresholds were significantly elevated in both CD subgroups compared to controls. Proprioceptive acuity of both the dystonic and nondystonic body segments was elevated in patients with CD and tremor with respect to both healthy controls and patients with CD without tremor. That is, tactile abnormalities were a shared dysfunction of both CD phenotypes, while proprioceptive dysfunction was observed in patients with CD with tremor.ConclusionsOur findings suggest that the pathophysiology in CD can be characterized by 2 abnormal neural processes: a dysfunctional somatosensory gating mechanism involving the basal ganglia that triggers involuntary muscle spasms and abnormal processing of proprioceptive information within a defective corticocerebellar loop, likely affecting the feedback and feedforward control of head positioning. This dysfunction is expressed mainly in CD with tremor.
Bibliographical noteFunding Information:
L. Avanzino received honoraria from the Michael J .Fox Foundation for the Fox Trial Finder project and research support from the Jacques und Gloria Gossweiler Foundation. A. Cherif, O. Crisafulli, F. Carbone, J. Zenzeri, and P. Morasso report no disclosures relevant to the manuscript. G. Abbruzzese received honoraria from Zambon for Advisory Board participation and from ApoPharma Inc for Data Safety Monitoring Board participation. E. Pelosin received honoraria from the Michael J. Fox Foundation for the Fox Trial Finder project and a research grant from the Michael J. Fox Foundation. J. Konczak received research support through US National Science Foundation (IIP-1937557), US National Science Foundation (IIP-1745306), Children Cancer Research Fund of the University of Minnesota Medical School, and US NIH (R01 DC016315–01, UL1TR000114, and 5U01-HL127479-02). Go to https://n.neurology.org/lookup/doi/10.1212/WNL.0000000000008916 for full disclosures.
© American Academy of Neurology.