Soleus H-reflex tests and clinical signs of the upper motor neuron syndrome.

Soleus H-reflex tests are used for elucidating pathophysiological mechanisms in motor control. The cumulative vibratory inhibition of the soleus H-reflex, the ratio of the reflex to direct muscle potential (H to M ratio) and the recovery curve of the soleus H-reflex were studied in 38 patients with varying signs of the upper motor neuron syndrome for a possible relation with clinical features. The results were compared with those obtained from a group of healthy volunteers. The magnitude of vibratory inhibition decreased with increase of hypertonia. The H to M ratio increased as the activity of the tendon reflex was enhanced and correlated to a lesser degree with muscle tone. Both the H to M ratio and late facilitation of the soleus H-reflex recovery curve were elevated in clonus. The findings suggest that alterations in the results of soleus H-reflex tests relate to specific clinical features of the upper motor neuron syndrome. Possible pathophysiological implications are discussed.

Soleus H-reflex tests in spasticity and dystonia: A computerized analysis.

In 54 healthy individuals, and in 25 spastic and 7 dystonic subjects, soleus H-reflex vibratory inhibition, H M ratio, and homonymous recovery curves obtained at two stimulus intensity levels were investigated in the same subject. In spasticity, the most prominent changes consist of a diminution of the vibratory inhibition at stimulus intensities lower than needed for a maximum H-reflex and an increase in the H M ratio. These results suggest that presynaptic inhibition is reduced mainly at low-intensity levels and that excitability of motoneurons is increased. Recovery curves in spasticity do not show such significant changes as found for the recruitment curves. In dystonia, prominent changes occur in the late facilitatory phase of the recovery curve obtained at 0.5 H(max) stimulus intensity, suggesting increased interneuronal activity. Vibratory suppression may be diminished, but H M ratio is unaltered. A multivariate analysis was used to identify variables that discriminated between control, spastic, and dystonic subjects. The analysis yielded two canonical variables that are a linear combination of four H-reflex variables that contribute significantly to the group classification. Based on these two canonical variables, each group can be properly differentiated quantitatively.