Peripheral and central effect of baclofen on ankle joint stiffness in multiple sclerosis

The effect of baclofen on the soleus stretch reflex and peripheral muscle f unction was tested in 10 multiple sclerosis (MS) patients with spasticity i n the lower extremities. Peroral baclofen (15-60 mg daily) induced a decrea se in the twitch torque of the soleus muscle elicited by supramaximal nerve stimulation, The torque was 15.1 +/- 5.5 Nm with baclofen and 17.1 +/- 5.0 Nm without baclofen (P = 0.03). The slope of the background torque/EMG rel ation was also changed from 1.53 Nm/mu V with baclofen to 1.13 NM/mu V with out it (P = 0.03), and the soleus stretch reflex threshold decreased from 1 1.4 degrees/s (3.1-62.8) to 6.2 degrees/s (3.1-25.1) without baclofen medic ation (P = 0.03) in the relaxed muscle. Furthermore, baclofen induced an ap proximately 20% decrease in the total stiffness at the ankle joint at ail c ontraction levels due to a decrease in the short-latency stretch reflex. Fr om a clinical point of view, the peripheral action of baclofen may be unfor tunate. Spasticity is often accompanied by weakness, which may be the major cause of any disability. Consequently, reduction in spasticity by the cent ral effect of baclofen may be counteracted by its influence on muscle prope rties. in addition, treatment of spasticity by baclofen may unmask weakness . (C) 2000 John Wiley & Sons, Inc.