Vibratory inhibition, the homonymous recovery curve and the ratio of t
he maximal H-reflex to direct muscle potential (H/M ratio) of the sole
us H-reflex were assessed in 10 patients with leg dystonia and in six
patients with arm or neck dystonia. The results were compared with tho
se obtained in 48 healthy control subjects. H-reflex variables most he
lpful for the discrimination of patients and healthy subjects were ide
ntified. In patients with leg dystonia, vibratory inhibition was less
marked than in control subjects, whereas late facilitation of the reco
very curve was increased. In patients with leg dystonia, area values o
f test reflexes in the late facilitatory phase of the recovery curve e
xceeded peak-peak values, in contrast to findings in control subjects.
This finding may be attributable to less synchronization of enhanced
test reflexes in dystonia than in the control condition. In differenti
ating patients with leg dystonia from control subjects, a combination
of parameters of vibratory inhibition and the late facilitatory phase
of the recovery curve appeared most useful. In patients with arm or ne
ck dystonia and in the unaffected legs of hemidystonic patients, soleu
s H-reflex test results were in the normal range. Abnormalities in the
results of the soleus H-reflex tests we used appear to be related to
the presence of clinical signs in the extremity under examination and
not to the severity of features.