DOPA-RESPONSIVE DYSTONIA AND NORMALIZATION OF SOLEUS H-REFLEX TEST-RESULTS WITH TREATMENT

We studied the ratio of the maximal II-reflex to maximal direct muscle potential (H/M ratio), late facilitation and late inhibition in the r ecovery curve, and vibratory inhibition of the soleus H-reflex in thre e consecutive patients with hereditary dopa-responsive dystonia, befor e and during treatment with levodopa. In one patient, we repeated the H-reflex tests twice after withdrawal of levodopa. The results were co mpared with those in a group of 48 healthy subjects. In the patients b efore treatment, the soleus H-reflex recovery curve showed increased l ate facilitation and depressed late inhibition, reflecting alterations in postsynaptic interneuronal activity. Vibratory inhibition, predomi nantly reflecting presynaptic inhibitory action, was depressed. Normal ization of these test results occurred during levodopa treatment, conc urrent with a clear clinical response. The H/M ratio, reflecting the e xcitability state of the motoneuron pool, was similar during and witho ut levodopa treatment. In the one patient tested after levodopa withdr awal, enhancement of late facilitation and decrease of vibratory inhib ition paralleled the reoccurrence of dystonia most clearly. Since sole us H-reflex tests mainly reflect mechanisms operating at the spinal le vel, spinal aminergic or dopaminergic systems are probably involved in dopa-responsive dystonia.