Characterizations of reflex and nonreflex changes in spastic multiple sclerosis.
BACKGROUND
Spasticity, an increased resistance of a limb to movement, is associated with functional limitations and a major source of disability in neurological disorders, including multiple sclerosis (MS) and stroke. Despite the clinical significance of spasticity in brain and spinal cord injuries, it is often not clear whether the spasticity is due to reflex or non-reflex changes.


METHODS
Reflex and nonreflex properties of the human knee joint were studied in eight MS patients with spasticity and ten healthy subjects. A digitally controlled joint driving device was used to apply small-amplitude, and band-limited white-noise perturbations to the knee to manifest the reflex and nonreflex properties. The subjects were asked to maintain a steady level of background muscle torque during the perturbation. A nonlinear delay differential equation model was used to characterize the reflex and intrinsic properties of the knee in terms of phasic stretch reflex gain, tonic stretch reflex gain, joint elastic stiffness, and coefficient of viscosity.


RESULTS
It was found that joint coefficient of viscosity and tonic stretch reflex gain of the spastic MS patients were significantly lower than those of normal controls. On the other hand, spastic MS patients showed higher phasic stretch reflex gains than normal controls and a trend of increased joint stiffness.


CONCLUSIONS
Simultaneous characterizations of changes in tonic and phasic reflexes and nonreflex changes in joint elastic stiffness and viscosity in neurological disorders may help us gain insight into mechanisms underlying spasticity and develop impairment-specific treatment.
Rehabilitation Institute of Chicago, 345 East Superior Street, Chicago, Illinois 60611, USA; Department of Physical Medicine and Rehabilitation, Northwestern University, 345 East Superior Street, Chicago, Illinois 60611, USA; Department of Orthopaedic Surgery, Northwestern University, 676 N. St. Clair Street, Chicago, Illinois 60611, USA; Department of Biomedical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA. Electronic address: l-zhang@northwestern.edu.
Li-Qun
LQ
Zhang
Rehabilitation Institute of Chicago, 345 East Superior Street, Chicago, Illinois 60611, USA.
Kai
K
Chen
Rehabilitation Institute of Chicago, 345 East Superior Street, Chicago, Illinois 60611, USA.
Sang Hoon
SH
Kang
Rehabilitation Institute of Chicago, 345 East Superior Street, Chicago, Illinois 60611, USA; Department of Physical Medicine and Rehabilitation, Northwestern University, 345 East Superior Street, Chicago, Illinois 60611, USA.
James A
JA
Sliwa
Davee Department of Neurology and Clinical Neurosciences, Northwestern University, 710 North Lake Shore Drive, Chicago, IL 60611, USA.
Bruce A
BA
Cohen
Rehabilitation Institute of Chicago, 345 East Superior Street, Chicago, Illinois 60611, USA; Department of Physical Medicine and Rehabilitation, Northwestern University, 345 East Superior Street, Chicago, Illinois 60611, USA; Department of Physiology, Northwestern University, 310 E. Superior Street, Chicago, Illinois 60611, USA.
W Z
WZ
Rymer
Rehabilitation Institute of Chicago, 345 East Superior Street, Chicago, Illinois 60611, USA.
Liang
L
Wang
D056044:Actigraphy / Q000295:instrumentation; D000328:Adult; D004548:Elasticity; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D009103:Multiple Sclerosis / Q000503:physiopathology*; D009128:Muscle Spasticity / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000503:physiopathology; D017711:Nonlinear Dynamics; D010812:Physical Stimulation; D012026:Reflex, Stretch / Q000502:physiology*; D019415:Torque; D014783:Viscosity
Knee; Multiple Sclerosis; Spasticity; Stiffness; Stretch reflex; Viscosity