Pathological stretch reflexes on the "good" side of hemiparetic patients.

Abstract

The reflex EMG responses from a tendon tap or an imposed, medium amplitude (300), stretch at a range of stretch velocities have been recorded from the triceps and biceps muscles of normal human subjects and in both the affected and "unaffected" arms of hemiparetic patients under relaxed conditions. In the hemiparetic arm, exaggerated tendon jerks were, as expected, observed in both muscles. The response of the biceps to elbow extension was also exaggerated compared with normal values and displayed both an additional, earlier component and a much reduced velocity threshold. The triceps, in contrast, showed depressed responses to elbow flexion, with a much higher velocity threshold than normal subjects. Furthermore, on the supposedly "unaffected" side of the hemiparetic subjects, the reciprocal pattern was seen, with depression of the biceps response and a raising of its threshold, along with considerably exaggerated responses in the triceps including earlier components not seen in the normal subjects. The increased excitability of the flexor musculature on the spastic side may be paralleled by increases in activity in the segmental pathways responsible for modulation of agonist/antagonist activity in the ipsi and contralateral limb, leading to an inhibition of the ipsilateral extensors and contralateral flexors and excitatory input to the contralateral extensors. Thus the "good" side of hemiparetic patients also receives pathological changes, and studies of the mechanisms of spasticity should avoid the use of the "unaffected" side of hemiparetic subjects as a control for monitoring pathological reflexes.

Efficiency of work production by spastic muscles

“…The PHL showed some signs of perturbed motor control and was not absolutely ''normal''. In 10 hemiparetic patients, Thilmann et al [26] found increased EMG responses to stretch in the healthy triceps of hemiparetic patients, with shorter latency activity on the healthy side of hemiparetic subjects. The biceps presented a depression of the EMG response to stretch, with a decreased biceps tendon reflex (p < 0.001).…”

Spastic movement disorder

“…In such a condition a displacement of the elbow joint is associated with an increased EMG activity in the stretched muscles of the spastic side compared to the una ected side in patients with spastic hemiparesis. 19,26 Nevertheless, subsequent studies analyzing the di erent components which contribute to muscle tone clearly revealed that muscle hypertonia is more associated with muscle ®bre contracture than with re¯ex hyperexcitability. 11,27 Studies on muscle tone and re¯ex activity have usually been performed under passive motor conditions.…”

“…11,27 Studies on muscle tone and re¯ex activity have usually been performed under passive motor conditions. 26,28 In such a condition, increased elbow torque following a displacement was associated with an increased EMG activity in the¯exor muscles of the spastic side compared to the una ected side in patients with spastic hemiparesis. 19 Nevertheless, spastic muscle hypertonia was found to be closely associated with muscle ®bre contracture but not with re¯ex hyperexcitability.…”

Neuromuscular Abnormalities Associated With Spasticity of Upper Extremity Muscles in Hemiparetic Stroke

“…The experiment was performed on both paretic and nonparetic elbow joints. Although the nonparetic limb may sometimes have minor detectable impairments (Thilmann et al 1990), it was designated as a control for the impaired limb because it is not spastic and has similar musculo-tendon architecture and limb mass. However, to control for possible changes in the nonparetic side, we used healthy age-matched subjects as secondary or additional controls.…”