Modulation of the transmission in group II heteronymous pathways by tizanidine in spastic hemiplegic patients

Objective: To investigate the effect of tizanidine (an α2 noradrenergic agonist) on transmission in the interneuronal pathway coactivated by group I and group II afferents in post-stroke patients with spastic hemiplegia. Methods: Early and late facilitation of the quadriceps H reflex elicited in the common peroneal nerve—attributed to non-monosynaptic group I and group II excitation, respectively—was investigated in 14 spastic hemiplegic patients. All received a single dose of tizanidine (150 μg/kg) or placebo in randomised order at 10 day intervals. Repeated measurements were made at baseline (T0), 45–90 min, and 120 min after drug intake. Spasticity was assessed by modified Ashworth score in the quadriceps muscle and by a leg tone score calculated by the sum of the modified Ashworth score in five muscle groups. Results: On the spastic side a decrease in late group II and, to a lesser extent, early group I common peroneal nerve induced quadriceps H reflex facilitation occurred with tizanidine (group II, mean (SEM) difference T0–T90: 34.3 (10.2)%, p