Quantitative assessment of intrathecally administered baclofen in spasticity.

OBJECTIVE: To quantitatively assess the antispastic effect of intrathecally administered baclofen on muscle stiffness in spastic patients. DESIGN: Case-control study. SETTING: Clinical laboratory in a university hospital of a city of more than 1,000,000 inhabitants. PARTICIPANTS: Eighteen healthy adult volunteers (9 men, 9 women) were recruited for establishing the normal values. Eleven spastic patients (8 men, 3 women) comprised the study group. MAIN OUTCOME MEASURES: The resistance to passive sinusoidal displacement of 5 degrees imposed to the ankle joint was measured at frequencies from 3 to 12 Hz. Torque and displacement signals were subjected to a Fourier analysis to isolate the elastic and viscous components of the total muscle stiffness. RESULTS: In comparison with the period before intrathecal injection, and with the control group, it was shown that at 4 hours after injection, stretch reflex activity was abolished and elastic and viscous muscle stiffness approached control values. The abnormal residual stiffness concerned only the elastic component due to chronic transformations of the spastic muscle and/or due to changes in joints and periarticular connective tissue. This antispastic effect was completely reversed 36 hours after injection. CONCLUSION: The present study shows that the antispastic effect of intrathecally administered baclofen in spastic patients can be quantitatively assessed by a sensitive method allowing measurement of elastic and viscous components of muscle stiffness