Journal
EXPERIMENTAL NEUROLOGY
Volume 208, Issue 1, Pages 38-46Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.expneurol.2007.07.002
Keywords
Parkinson's disease; muscle tone; hypertonicity; rigidity; levodopa; axial musculature
Categories
Funding
- NIA NIH HHS [R01 AG006457, AG006457, R37 AG006457, R01 AG006457-18] Funding Source: Medline
- NINDS NIH HHS [T32 NS045553, NS45553] Funding Source: Medline
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A cardinal feature of Parkinson's disease (PD) is muscle hypertonicity, i.e. rigidity. Little is known about the axial tone in PD or the relation of hypertonia to functional impairment. We quantified axial rigidity to assess its relation to motor symptoms as measured by UPDRS and determine whether rigidity is affected by levodopa treatment. Axial rigidity was measured in 12 PD and 14 age-matched controls by directly measuring torsional resistance of the longitudinal axis to twisting (+/- 10 degrees). Feet were rotated relative to fixed hips (Hip Tone) or feet and hips were rotated relative to fixed shoulders (Trunk Tone). To assess tonic activity only, low constant velocity rotation (I degrees/s) and low acceleration (< 12 degrees/s(2)) were used to avoid eliciting phasic sensorimotor responses. Subjects stood during testing without changing body orientation relative to gravity. Body parts fixed against rotation could translate laterally within the boundaries of normal postural sway, but could not rotate. PD OFF-medication had higher axial rigidity (p < 0.05) in hips (5.07 N m) and trunk (5.30 N m) than controls (3.51 N m and 4.46 N m, respectively), which did not change with levodopa (p > 0.10). Hip-to-trunk torque ratio was greater in PD than controls (p < 0.05) and unchanged by levodopa (p = 0.28). UPDRS scores were significantly correlated with hip rigidity for PD OFF-medication (r values = 0.73, p < 0.05). Torsional resistance to clockwise versus counter-clockwise axial rotation was more asymmetrical in PD than controls (p < 0.05), however, there was no correspondence between direction of axial asymmetry and side of disease onset. In conclusion, these findings concerning hypertonicity may underlie functional impairments of posture and locomotion in PD. The absence of a levodopa effect on axial tone suggests that axial and appendicular tones are controlled by separate neural circuits. (c) 2007 Elsevier Inc. All rights reserved.
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