Lack of modulation of Ib inhibition during antagonist contraction in spasticity.
OBJECTIVE
To examine the modulation of non-reciprocal group I (Ib) inhibition during tonic contraction of antagonist muscles in patients with spasticity vs normal subjects.


METHODS
The authors studied 10 patients with spastic paraplegia due to cervical compression myelopathy and 16 age-matched normal subjects. Ib inhibition to soleus motoneurons was recorded as the change in size of the H-reflex of the soleus, evoked by conditioning stimulus to the nerve innervating the medial gastrocnemius muscle. The extent of inhibition was studied at rest and during tonic contraction of the pretibial muscles of variable strength.


RESULTS
In the resting state, the extent of inhibition in the patients did not differ from normal controls. During antagonist contraction, the extent of inhibition increased both in the normal subjects and patients. The increment was smaller in the patients, especially in those with severe spastic gait. The smaller increment in the inhibition was correlated with the time required to walk 10 m in the patients.


CONCLUSIONS
The authors observed a lack of modulation of Ib inhibition during tonic antagonist contraction in patients with spasticity, especially those with gait disturbance. Disturbed central modulation of non-reciprocal (Ib) interneurons may be responsible for spasticity.
Morita
H
H
Department of Medicine, Shinshu University School of Medicine, Japan. hmorita@hsp.md.shinshu-u.ac.jp
Shindo
M
M
Momoi
H
H
Yanagawa
S
S
Ikeda
S
S
Yanagisawa
N
N
D000368:Aged; D016022:Case-Control Studies; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D009128:Muscle Spasticity / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000503:physiopathology; D009433:Neural Inhibition; D010264:Paraplegia / Q000150:complications / Q000503:physiopathology*; D016192:Resting Phase, Cell Cycle / Q000502:physiology / Q000528:radiation effects; D013979:Tibial Nerve / Q000528:radiation effects; D013997:Time Factors