A comparative study of methods for estimation of presynaptic inhibition.

The influence of vibration on the H-reflex and on the tendon reflex amplitudes was compared and the efficacy of both methods for the assessment of the presynaptic inhibition was studied. One hundred and twenty patients with post-stroke spastic hemiparesis were investigated. Muscle tone, muscle force and tendon reflexes were assessed. The H-reflex and the Achilles tendon reflex (TA) were recorded under identical experimental conditions. Vibration at a frequency of 100 Hz and an amplitude of 2 mm was applied to the TA. Just after vibration the maximal amplitudes of both reflexes were measured. The ratios of reflex amplitudes after vibration to normal maximal reflex amplitudes (Hvibr/Hmax and TAvibr/TAmax) were evaluated. In all patients with hemiparesis the healthy side was used as a control. Our results revealed significantly increased amplitude ratios on the spastic side. Hence it is concluded that presynaptic inhibition is decreased in spasticity. The amplitude ratios on the healthy and the spastic side were consistent. There was good positive correlation between Hvibr/Hmax and TAvibr/TAmax ratios, suggesting that they provide similar and reliable estimates of presynaptic inhibition.